OCR Level 1/2 GCSE (Grade 9-1) in Physics B (Twenty First Century Science) (J259) and OCR Level 1/2 GCSE (Grade 9-1) in Combined Science B Physics (Twenty First Century Science) (J260)
OCR 21st Century GCSE Grade 9-1 PHYSICS B/Combined Science Revision Summaries for Chapters 4,5 and 6
Syllabus-specification CONTENT INDEX of revision summary notes
These are my NEW revision summaries for Y10 starting in September 2016, first exams from May-June 2018 onwards. ALL my unofficial GCSE (Grade 9-1) revision help is based on the NEW 2016 official OCR Twenty First Century Science (Grade 9-1) GCSE physics/combined science specifications
Make sure you know whether you are doing separate OCR Twenty First Century Science GCSE Grade 9-1 PHYSICS OR OCR Twenty First Century Science GCSE Grade 9-1 Combined Science physics, BOTH are covered on this page and one other page! (OCR Twenty First Century Combined Science course students do NOT need to know all learning objectives on this page - all such sections NOT needed are indicated by GCSE PHYSICS ONLY)
The Google [SEARCH] box at the bottom of the page should also prove useful
Be aware that both Physics Papers 1 and Paper 2 assess the content from ALL 6 chapters !!!
(HT only) means higher tier only (NOT FT foundation tier) and (GCSE physics only) means for the separate science only, NOT for Combined Science physics
Syllabus-specification CONTENT INDEX
Revision SUMMARY Chapter P4: Be able to explaining motion (this page)
Revision SUMMARY Chapter P5: Radioactive materials (this page)
Revision SUMMARY Chapter P6: Matter – models and explanations (this page)
Revision SUMMARY Chapter P7: Ideas about Science (this page)
Chapter P4: Be able to explaining motion
Simple but counterintuitive concepts of forces and motion, developed by Galileo and Newton, can transform your insight into everyday phenomena. These ideas also underpin an enormous range of modern applications, including spacecraft, urban mass transit systems, sports equipment and rides at theme parks.
Topic P4.1 reviews the idea of forces: identifying, describing and using forces to explain simple situations.
Topic P4.2 looks at how speed is measured and represented graphically and introduces the vector quantities of velocity and displacement. The relationships between distance, speed, acceleration and time are an example of simple mathematical modelling that can be used to predict the speed and position of a moving object.
The relationship between forces and motion is developed in Topic P4.3, where resultant forces and changes in momentum are described. These ideas are then applied in the context of road safety.
Topic P4.4 considers how we can describe motion in terms of energy transfers.
What you should have learned and experienced from KS3 science about force and motion ...
Chapter P4.1 What are forces?
Force arises from an interaction between two objects, and when two objects interact, both always experience a force and that these two forces form an interaction pair. The two forces in an interaction pair are the same kind of force, equal in size and opposite in direction, and act on different objects (Newton’s third law).
Friction is the interaction between two surfaces that slide (or tend to slide) relative to each other: each surface experiences a force in the direction that prevents (or tends to prevent) relative movement.
There is an interaction between an object and the surface it is resting on: the object pushes down on the surface, the surface pushes up on the object with an equal force, and this is called the normal contact force.
In everyday situations, a downward force acts on every object, due to the gravitational attraction of the Earth. This is called its weight. It can be measured (in N) using a spring (or top-pan) balance. The weight of an object is proportional to its mass. Near the Earth’s surface, the weight of a 1 kg object is roughly 10 N. The Earth’s gravitational field strength is therefore 10 N/kg.
Newton’s insight that linked the force that causes objects to fall to Earth with force that keeps the Moon in orbit around the Earth led to the first universal law of nature.
1. Be able to recall and apply Newton’s Third Law.
2. Be able to recall examples of ways in which objects interact: by gravity, electrostatics, magnetism and by contact (including normal contact force and friction).
3. Be able to describe how examples of gravitational, electrostatic, magnetic and contact forces involve interactions between pairs of objects which produce a force on each object.
4. Be able to represent interaction forces as vectors.
5. Be able to define weight.
6. Be able to describe how weight is measured.
7. Be able to recall and apply the relationship between the weight of an object, its mass and the gravitational field strength using the formula:
Chapter P4.2 How can we describe motion?
The motion of a moving object can be described using the speed the object is moving, the direction it is travelling and whether the speed is changing.
The distance an object has travelled at a given moment is measured along the path it has taken.
The displacement of an object at a given moment is its net distance from its starting point together with an indication of direction.
The velocity of an object at a given moment is its speed at that moment, together with an indication of its direction.
Distance and speed are scalar quantities; they give no indication of direction of motion.
Displacement and velocity are vector quantities, and include information about the direction.
In everyday situations, acceleration is used to mean the change in speed of an object in a given time interval.
Distance–time graphs and speed-time graphs can be used to describe motion. The average speed can be calculated from the slope of a distance–time graph.
The average acceleration of an object moving in a straight line can be calculated from a speed-time graph. The distance travelled can be calculated from the area under the line on a speed-time graph.
The mathematical relationships between acceleration, speed, distance, and time are a simple example of a computational model. The model can be used to predict the speed and position of an object moving at constant speed or with constant acceleration.
1. Be able to recall and apply the relationship: average speed (m/s) = distance (m) ÷ time (s)
2. Be able to recall typical speeds encountered in everyday experience for wind, and sound, and for walking, running, cycling and other transportation systems.
3. (a) Be able to make measurements of distances and times, and calculate speeds.
3. (b) Be able to describe how to use appropriate apparatus and techniques to investigate the speed of a trolley down a ramp.
4. make calculations using ratios and proportional reasoning to convert units, to include between m/s and km/h.
5. Be able to explain the vector-scalar distinction as it applies to displacement and distance, velocity and speed.
6. (a) Be able to recall and apply the relationship:
6. (b) Be able to explain how to use appropriate apparatus and techniques to investigate acceleration
7. Be able to select and apply the relationship:
8. Be able to draw and use graphs of distances and speeds against time to determine the speeds and accelerations involved.
9. Be able to interpret distance-time and velocity-time graphs, including relating the lines, slopes and enclosed areas in such graphs to the motion represented.
10. Be able to interpret enclosed areas in velocity – time graphs.
11. Be able to recall the value of acceleration in free fall and calculate the magnitudes of everyday accelerations using suitable estimates of speeds and times.
Chapter P4.3 What is the connection between forces and motion?
When forces act on an object the resultant force is the sum of all the individual forces acting on it, taking their directions into account.
(HT only) If a resultant force acts on an object, it causes a change of momentum in the direction of the force. The size of the change of momentum of an object is proportional to the size of the resultant force acting on the object and to the time for which it acts (Newton’s second law).
For an object moving in a straight line:
(HT only) In situations involving a change in momentum (such as a collision), the longer the duration of the impact, the smaller the average force for a given change in momentum.
In situations where the resultant force on a moving object is not in the line of motion, the force will cause a change in direction.
1. Be able to describe examples of the forces acting on an isolated solid object or system.
2. Be able to describe, using free body diagrams, examples where several forces lead to a resultant force on an object and the special case of balanced forces (equilibrium) when the resultant force is zero (qualitative only).
3. (HT only) Be able to use scale drawings of vector diagrams to illustrate the addition of two or more forces, in situations when there is a net force, or equilibrium (limited to parallel and perpendicular vectors only).
4. (HT only) Be able to recall and apply the equation for momentum and describe examples of the conservation of momentum in collisions:
5. (HT only) Be able to select and apply Newton's second law in calculations relating force, change in momentum and time:
(HT only) If the force is perpendicular to the direction of motion the object will move in a circle at a constant speed – the speed doesn’t change but the velocity does. For example, a planet in orbit around the Sun – gravity acts along the radius of the orbit, at right angles to the planet’s path.
6. Be able to apply Newton’s first law to explain the motion of objects moving with uniform velocity and also the motion of objects where the speed and/or direction changes.
7. (HT only) Be able to explain with examples that motion in a circular orbit involves constant speed but changing velocity qualitative only (qualitative only, no calculations to do!).
In some situations a resultant force acts to make an object rotate about a fixed point (pivot).
The rotational effect is called the moment of the force; the further the force acts from the pivot, the greater the turning effect.
Levers and gears are used to transmit rotational forces.
8. (GCSE Physics only) Be able to describe examples in which forces cause rotation.
9. (GCSE Physics only) Be able to define and calculate the moment of examples of rotational forces using the equation:
10. (GCSE Physics only) Be able to explain, with examples, how levers and gears transmit the rotational effects of forces
The mass of an object can be thought of as the amount of matter in an object – the sum of all the atoms that make it up. Mass is measured in kilograms. The mass of an object is also a measure of its resistance to any change in its motion (its inertia); using this definition the inertial mass is the ratio of the force applied to the resulting acceleration.
(HT only) Newton wrote about how the length of time a force acted on an object would change the object’s ‘amount of motion’ , and the way he used the term makes it clear that he is describing what we now call momentum, this has led to Newton’s second law being expressed in two ways – in terms of change in momentum and in terms of acceleration.
Newton’s explanation of motion is one of the great intellectual leaps of humanity. It is a good example of the need for creativity and imagination to develop a scientific explanation of something that had been observed and discussed for many years.
GCSE Physics/Combined Science learning objectives
11./8. (HT only) Be able to explain that inertial mass is a measure of how difficult it is to change the velocity of an object and that it is defined as the ratio of force over acceleration.
12./9. Be able to recall and apply the equation of Newton's 2nd law relating force, mass and acceleration:
Ideas about force and momentum (HT only) can be used to explain road safety measures, such as stopping distances, car seatbelts, crumple zones, air bags, and cycle and motorcycle helmets.
Improvements in technology based on Newton’s laws of motion (together with the development of new materials) have made all forms of travel much safer.
13./10 Be able to use and apply equations relating force, mass, velocity, acceleration, and momentum (HT only) to explain relationships between the quantities.
14.11. Be able to explain methods of measuring human reaction times and recall typical results.
15./12. Be able to explain the factors which affect the distance required for road transport vehicles to come to rest in emergencies and the implications for safety.
16./13. Be able to explain the dangers caused by large decelerations and (HT only) estimate the forces involved in typical situations on a public road.
17. (GCSE Physics only) Be able to, given suitable data, estimate how the distance required for road vehicles to stop in an emergency, and describe how the distance varies over a range of typical speeds.
18. (GCSE Physics only) Be able to, in the context of everyday road transport, use estimates of speeds, times and masses to calculate the accelerations and forces involved events where large accelerations occur.
Chapter P4.4 How can we describe motion in terms of energy transfers?
Energy is always conserved in any event or process. Energy calculations can be used to find out if something is possible and what will happen, but not explain why it happens.
The store of energy of a moving object is called its kinetic energy.
As an object is raised, its store of gravitational potential energy increases, and as it falls, its gravitational potential energy decreases.
When a force moves an object, it does work on the object, energy is transferred to the object; when work is done by an object, energy is transferred from the object to something else, for example:
If friction and air resistance can be ignored, an object’s store of kinetic energy changes by an amount equal to the work done on it by an applied force; in practice air resistance or friction will cause the gain in kinetic energy to be less than the work done on it by an applied force in the direction of motion, because some energy is dissipated through heating.
Calculating the work done when climbing stairs or lifting a load, and the power output, makes a link back to the usefulness of electrical appliances for doing many everyday tasks.
1. Be able to describe the energy transfers involved when a system is changed by work done by forces including
2. Be able to recall and apply the relationship to calculate the work done (energy transferred) by a force:
3. Be able to recall the equation and calculate the amount of energy associated with a moving object:
4. Be able to recall the equation and calculate the amount of energy associated with an object raised above ground level.
5. Be able to make calculations of the energy transfers associated with changes in a system, recalling relevant equations for mechanical processes.
6. Be able to calculate relevant values of stored energy and energy transfers; convert between newton-metres and joules.
7. Be able to describe all the changes involved in the way energy is stored when a system changes, for common situations: including an object projected upwards or up a slope, a moving object hitting an obstacle, an object being accelerated by a constant force, a vehicle slowing down.
8. Be able to explain, with reference to examples, the definition of power as the rate at which energy is transferred (work done) in a system.
9. Be able to recall and apply the relationship: power (W) = energy transferred (J) / time (s)
Chapter P5: Radioactive materials
The terms ‘radiation’ and ‘radioactivity’ are often interchangeable in the public mind. Because of its invisibility, radiation is commonly feared. A more objective evaluation of risks and benefits is encouraged through developing an understanding of the many practical uses of radioactive materials.
In Topic P5.1 you study the evidence of a
nuclear model of the atom, including Rutherford’s alpha particle scattering
experiment. It then uses the nuclear model to explain what happens during
radioactive decay. The properties of alpha, beta and
In Topic P5.2 learners learn about the penetration properties of ionising radiation which leads to a consideration of the use of radioactive materials in the health sector, and how they can be handled safely. In the context of health risks associated with irradiation and/or contamination by radioactive material, they also learn about the interpretation of data on risk.
Topic P5.3 (GCSE Physics only) describes nuclear fission and nuclear fusion. Learners have the opportunity to learn more about the issues that surround decisions about the best way to generate electricity.
What you should have learned and experienced from KS3 science about ? ...
P5.1 What is radioactivity?
An atom has a nucleus, made of protons and neutrons, which is surrounded by electrons.
The modern model of the atom developed over time as scientists rejected earlier models and proposed new ones to fit the currently available evidence.
Each stage relied on scientists using reasoning to propose models which fitted the evidence available at the time. Models were rejected, modified and extended as new evidence became available (IaS3).
After the discovery of the electron in the 19th century by Thomson scientists imagined that atoms were small particles of positive matter with the negative electrons spread through, like currants in a cake.
This was the model used until 1910 when the results of the Rutherford-Geiger-Marsden alpha particle scattering experiment provided evidence that a gold atom contains a small, massive, positive region (the nucleus).
Atoms are small – about 10–10 m across, and the nucleus is at the centre, about a hundred-thousandth of the diameter of the atom.
Each atom has a nucleus at its centre and that nucleus is made of protons and neutrons. For an element, the number of the protons is always the same but the number of neutrons may differ. Forms of the same element with different numbers of neutrons are called the isotopes of the element.
Interpreting the unexpected results of the Rutherford Geiger-Marsden experiment required imagination to consider a new model of the atom.
Some substances emit ionising radiation all the time and are called radioactive. The ionising radiation (alpha, beta, gamma, and neutron) is emitted from the unstable nucleus of the radioactive atoms, which as a result become more stable.
Alpha particles consist of two protons and two neutrons, and beta particles are identical to electrons. Gamma radiation is very high frequency electromagnetic radiation.
Radioactive decay is a random process. For each radioactive isotope there is a different constant chance that any nucleus will decay. Over time the activity of radioactive sources decreases, as the number of undecayed nuclei decreases.
The time taken for the activity to fall to half is called the half-life of the isotope and can be used to calculate the time it takes for a radioactive material to become relatively safe.
1. Be able to describe the atom as a positively charged nucleus surrounded by negatively charged electrons, with the nuclear radius much smaller than that of the atom and with almost all of the mass in the nucleus.
2. Be able to describe how and why the atomic model has changed over time to include the main ideas of Dalton, Thomson, Rutherford and Bohr.
3. Be able to recall the typical size (order of magnitude) of atoms and small molecules.
4. Be able to recall that atomic nuclei are composed of both protons and neutrons, and that the nucleus of each element has a characteristic positive charge.
5. Be able to recall that nuclei of the same element can differ in nuclear mass by having different numbers of neutrons, these are called isotopes.
6. Be able to use the conventional representation to show the differences between isotopes, including their identity, charge and mass.
7. Be able to recall that some nuclei are unstable and may emit alpha particles, beta particles, or neutrons, and electromagnetic radiation as gamma rays.
8. Be able to relate emissions of alpha particles, beta particles, or neutrons, and gamma rays to possible changes in the mass or the charge of the nucleus, or both.
9. Be able to use names and symbols of common nuclei and particles to write balanced equations that represent the emission of alpha, beta, gamma, and neutron radiations during radioactive decay.
10. Be able to explain the concept of half-life and how this is related to the random nature of radioactive decay.
11. (HT only) Be able to calculate the net decline, expressed as a ratio, in a radioactive emission after a given (integral) number of half-lives.
12. Be able to interpret activity-time graphs to find the half-life of radioactive materials.
Chapter P5.2: How can radioactive materials be used safely?
Ionising radiation can damage living cells and these may be killed or may become cancerous, so radioactive materials must be handled with care. In particular, a radioactive material taken into the body (contamination) poses a higher risk than the same material outside as the material will continue to emit ionising radiation until it leaves the body.
Whilst ionising radiation can cause cancer, it can also be used for imaging inside the body and to kill cancerous cells.
Doctors and patients need to consider the risks and benefits when using ionising radiation to treat diseases.
1. Be able to recall the differences in the penetration properties of alpha particles, beta particles and gamma rays.
2. Be able to recall the differences between contamination and irradiation effects and compare the hazards associated with each of these.
3. Be able to describe the different uses of nuclear radiations for exploration of internal organs, and for control or destruction of unwanted tissue.
4. Be able to explain how ionising radiation can have hazardous effects, notably on human bodily tissues.
5. Be able to explain why the hazards associated with radioactive material differ according to the radiation emitted and the half-life involved.
Chapter P5.3 How can radioactive materials be used to provide energy? (GCSE Physics only, NOT Combined Science)
Nuclear fuels are radioactive materials that release energy during changes in the nucleus.
In nuclear fission a neutron splits a large and unstable nucleus (such as some isotopes of uranium and plutonium) into two smaller parts, roughly equal in size, releasing more neutrons, which may go on to make further collisions.
Energy is released from the nucleus, carried away as kinetic energy of the particles and also by gamma radiation. This release of energy from the nuclear store is analogous to that released from the chemical store of explosives like TNT but it is considerably larger.
If brought close enough together, hydrogen nuclei can fuse into helium nuclei, releasing energy, and this is called nuclear fusion.
The demand for energy is continually increasing and nuclear fuels are an alternative energy source to fossil fuels. The risks and benefits need to be compared when making decisions about how to generate electricity.
1. Be able to recall that some nuclei are unstable and may split into two nuclei and that this is called nuclear fission.
2. Be able to relate the energy released during nuclear fission to the emission of ionising radiation and the kinetic energy of the resulting particles.
3. Be able to explain how nuclear fission can lead to further fission events in a chain reaction.
4. Be able to describe the process of nuclear fusion and be able to recall that in this process some of the mass may be converted into the energy of radiation.
Chapter P6: Matter – models and explanations
The famous quantum physicist Richard Feynman said: “If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms— little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.”
In chapter P6 the particle model described by Feynman is used to predict and explain some properties of matter.
Topic P6.1 explores the relationship between energy and temperature and the ways in which energy transfer transforms matter.
Topic P6.2 considers how the particle model explains the differences in densities between solids, liquids and gases and the effect of heating both in terms of temperature changes and changes of state.
Topic P6.3 considers the behaviour of materials under stress and how the particle model can explain differences in behaviour.
Topic 6.4 (GCSE Physics only) deals with pressure, and how it varies in fluids (liquids and gases), with the particle model used to explain the law discovered by Robert Boyle.
Finally, in Topic P6.5 (GCSE Physics only) ideas about forces and also the particle model are considered in the context of planets, moons and satellites in their orbit, and the formation of the solar system, before briefly describing the early stage of the Universe and the Big Bang.
What you should have learned and experienced from KS3 science about matter and particles ...
Chapter P6.1 How does energy transform matter?
It took the insight of a number of eighteenth and nineteenth century scientists to appreciate that heat and work were two aspects of the same quantity, which we call energy. Careful experiments devised by Joule showed that equal amounts of mechanical work would always produce the same temperature rise.
Energy can be supplied to raise the temperature of a substance by heating using a fuel, or an electric heater, or by doing work on the material.
Mass – the amount of matter in an object – depends on its volume and the density of the material of which it consists.
The temperature rise of an object when it is heated depends on its mass and the amount of energy supplied. Different substances store different amounts of energy per kilogram for each °C temperature rise – this is called the specific heat capacity of the material.
When a substance in the solid state is heated its temperature rises until it reaches the melting point of the substance, but energy must continue to be supplied for the solid to melt. Its temperature does not change while it melts, and the change in density on melting is very small. Similarly as a substance in the liquid state is heated its temperature rises until it reaches boiling point; its temperature does not change, although energy continues to be supplied while it boils. The change in density on boiling is very great; a small volume of liquid produces a large volume of vapour.
Different substances require different amounts of energy per kilogram to change the state of the substance – this is called the specific latent heat of the substance.
1. (a) Be able to define density
1. (b) Be able to describe how to determine the densities of solid and liquid objects using measurements of length, mass and volume.
2. Be able to recall and apply the relationship between density, mass and volume to changes where mass is conserved:
3. Be able to describe the energy transfers involved when a system is changed by heating (in terms of temperature change and specific heat capacity).
4. Be able to define the term specific heat capacity and distinguish between it and the term specific latent heat.
5. (a) Be able to select and apply the relationship between change in internal energy of a material and its mass, specific heat capacity and temperature:
5. (b) Be able to explain how to safely use apparatus to determine the specific heat capacity of materials.
The density change on boiling is very great; a small volume of liquid produces a large volume of vapour.
Different substances require different amounts of energy per kilogram to change the state of the substance – this is called the specific latent heat of the substance.
6. Be able to select and apply the relationship between energy needed to cause a change in state, specific latent heat and mass:
7. Be able to describe all the changes involved in the way energy is stored when a system changes, and the temperature rises, for example: a moving object hitting an obstacle, an object slowing down, water brought to a boil in an electric kettle.
8. Be able to make calculations of the energy transfers associated with changes in a system when the temperature changes, recalling or selecting the relevant equations for mechanical, electrical, and thermal processes.
Chapter P6.2 How does the particle model explain the effects of heating?
The particle model of matter describes the arrangements and behaviours of particles (atoms and molecules); it can be used to predict and explain the differences in properties between solids, liquids and gases. In this model:
The particle model is an example of how scientists use models as tools for explaining observed phenomena. The particle model can be used to describe and predict physical changes when matter is heated.
Careful experimentation and mathematical
analysis showed that the temperature of a substance was linked to the kinetic
energy of its atoms or molecules.
1. Be able to explain the differences in density between the different states of matter in terms of the arrangements of the atoms or molecules.
2. Be able to use the particle model of matter to describe how mass is conserved, when substances melt, freeze, evaporate, condense or sublimate and the material recovers its original properties if the change is reversed
3. Be able to use the particle model to describe how heating a system will change the energy stored within the system and raise its temperature or produce changes of state.
4. Be able to explain how the motion of the molecules in a gas is related both to its temperature and its pressure: hence explain the relation between the temperature of a gas and its pressure at constant volume (qualitative only, no calculations to do)
P6.3 How does the particle model relate to material under stress?
When more than one force is applied to a solid material it may be compressed, stretched or twisted. When the forces are removed it may return to its original shape or become permanently deformed.
These effects can be explained using ideas about particles in the solid state. A substance in the solid state is a fixed shape due to the forces between the particles.
Compressing or stretching the material changes the separation of the particles, and the forces between the particles.
Elastic materials spring back to their original shape. If the forces are too large the material becomes plastic and is permanently distorted.
For some materials, the extension is proportional to the applied force, but in other systems, such as rubber bands the relationship is not linear, even though they are elastic.
When work is done by a force to compress or stretch an spring or other simple system, energy is stored, this energy can be recovered when the force is removed.
1. Be able to explain, with examples, that to stretch, bend or compress an object, more than one force has to be applied.
2. Be able to describe and (HT only) use the particle model to explain the difference between elastic and plastic deformation caused by stretching forces.
3. (a) Be able to describe the relationship between force and extension for a spring and other simple systems.
3. (b) Be able to describe how to measure and observe the effect of forces on the extension of a spring.
4. Be able to describe the difference between the force-extension relationship for linear systems and for non-linear systems.
5. Be able to recall and apply the relationship between force, extension and spring constant for systems where the force-extension relationship is linear:
6. (a) Be able to calculate the work done in stretching a spring or other simple system, by calculating the appropriate area on the force-extension graph.
6. (b) Be able to describe how to safely use apparatus to determine the work done in stretching a spring.
7. Be able to select and apply the relationship between energy stored, spring constant and extension for a linear system:
P6.4 How does the particle model relate to pressures in fluids? (GCSE Physics only, NOT combined science)
An object immersed in a fluid (a liquid or a gas) experiences forces acting at right angles to all its surfaces due to the pressure of the fluid. The pressure of the fluid is due to collisions of the particles of the fluid with the surface of the object.
The particles of gas in a container collide with the surfaces of the container, exerting a pressure. If the volume of the container is increased, the particles have further to travel between collisions and the pressure of the gas falls. When a gas is compressed the particles are much closer together and will collide with the walls of the container more frequently, exerting a greater outward pressure.
The atmosphere of the Earth exerts a pressure perpendicular to the surface of any object in it, and this pressure is the same in all directions at a particular height. Atmospheric pressure decreases with height above the surface of the Earth.
The pressure at a point in a fluid increases with depth, because it is caused by the gravitational force on the fluid above that point. A fluid with greater density will experience a greater gravitational force and so exert a greater pressure.
Because pressure increases with depth, the force on the lower surface of an immersed object will be greater than the force on the upper surface, resulting in a net force upwards. This explains why the apparent weight of an object immersed in a liquid is less than its weight in air.
It was Dalton’s careful study of the atmosphere and gases that led to him giving a quantitative significance to the atomic theory which provides the basis for the particle model of matter.
1. Be able to recall that the pressure in fluids causes a force normal to any surface.
2. Be able to recall and apply the relationship between the force, the pressure, and the area in contact:
3. Be able to recall that gases can be compressed or expanded by pressure changes and that the pressure produces a net force at right angles to any surface.
4. Be able to use the particle model of matter to explain how increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure.
5. Be able to select and apply the equation:
6. Be able to describe a simple model of the Earth’s atmosphere and of atmospheric pressure, and explain why atmospheric pressure varies with height above the surface.
7. (HT only) Be able to explain why pressure in a liquid varies with depth and density.
8. (HT only) Be able to select and apply the equation to calculate the differences in pressure at different depths in a liquid:
9. (HT only) Be able to explain how the increase in pressure with depth in a fluid this leads to an upwards force on a partially submerged object.
10. (HT only) Be able to describe and explain the factors which influence whether a particular object will float or sink.
Chapter P6.5 How can scientific models help us understand the Big Bang? (GCSE Physics only, NOT comb. sci.)
The gravitational interaction between the planets and the Sun keeps the planets in (almost) circular orbits around the Sun, all in the same direction. Similarly, it is the gravitational interaction between a planet and its moons or artificial satellites that keeps them in orbit.
The force needed to keep an object moving in a circle depends on the speed of the object and the radius of the circle. The greater the speed and/or the smaller the radius, the greater the force needed. If a satellite or planet slows down, it will be pulled in to a smaller radius orbit.
The solar system was formed over long periods from clouds of gases and dust drawn together by the force of gravity. When a force is used to compress a gas, work is done on the gas, leading to an increase in temperature.
During the formation of a star such as the Sun, a cloud of gas is pulled together by gravity, its temperature increases and the hydrogen nuclei gain sufficient energy to fuse into helium nuclei, releasing more energy.
The Universe contains thousands of millions of galaxies. The light coming from distant galaxies shows a red-shift that suggests that distant galaxies are moving away from us. The further away a galaxy is, the faster it is moving away from us; this suggests that space itself is expanding. Scientists’ explanation for these observations is that the Universe began with a ‘Big Bang’ about 14 thousand million years ago.
The acceptance of the ‘Big Bang’ model to describe the early stages of the Universe depends on the interpretation of observations, as more observations were made, the theory became more secure.
Telescope designs have improved over the last 100 years, and modifications have made it possible to observe regions of the electromagnetic spectrum other than visible light. Placing these instruments outside the atmosphere has improved the range and quality of data obtained, and these improved data have increased the confidence in the ‘Big Bang’ model.
1. Be able to recall the main features of our solar system, including the similarities and distinctions between the planets, their moons, and artificial satellites.
2. (HT only) Be able to explain, for the circular orbits, how the force of gravity can lead to changing velocity of a planet but unchanged speed.
3. (HT only) Be able to explain how, for a stable orbit, the radius must change if this speed changes (qualitative only).
4. Be able to recall that the solar system was formed from dust and gas drawn together by gravity.
5. (HT only) Be able to use the particle model of matter to explain how doing work on a gas can increase its temperature (e.g. bicycle pump, in stars).
6. Be able to explain how the Sun was formed when collapsing cloud of dust and gas resulted in fusion reactions, leading to an equilibrium between gravitational collapse and expansion due to the fusion energy.
7. Be able to explain the red-shift of light from galaxies which are receding (qualitative only).
8. Be able to explain that relationship between the distance of each galaxy and its speed is evidence of an expanding universe model.
9. Be able to explain how the evidence of an expanding universe leads to the Big Bang model.
Chapter P7: Ideas about Science
Chapter IaS1 What needs to be considered when investigating a phenomenon scientifically?
The aim of science is to develop good explanations for natural phenomena. There is no single ‘scientific method’ that leads to good explanations, but scientists do have characteristic ways of working. In particular, scientific explanations are based on a cycle of collecting and analysing data. Usually, developing an explanation begins with proposing a hypothesis. A hypothesis is a tentative explanation for an observed phenomenon (“this happens because…”). The hypothesis is used to make a prediction about how, in a particular experimental context, a change in a factor will affect the outcome. A prediction can be presented in a variety of ways, for example in words or as a sketch graph. In order to test a prediction, and the hypothesis upon which it is based, it is necessary to plan an experimental strategy that enables data to be collected in a safe, accurate and repeatable way.
1. in given contexts use scientific theories and tentative explanations to develop and justify hypotheses and predictions
2. suggest appropriate apparatus, materials and techniques, justifying the choice with reference to the precision, accuracy and validity of the data that will be collected
3. recognise the importance of scientific quantities and understand how they are determined
4. identify factors that need to be controlled, and the ways in which they could be controlled
5. suggest an appropriate sample size and/or range of values to be measured and justify the suggestion
6. plan experiments or devise procedures by constructing clear and logically sequenced strategies to: make observations, produce or characterise a substance, test hypotheses, collect and check data and explore phenomena.
7. identify hazards associated with the data collection and suggest ways of minimizing the risk
8. use appropriate scientific vocabulary, terminology and definitions to communicate the rationale for an investigation and the methods used using diagrammatic, graphical, numerical and symbolic forms
Chapter IaS2 What conclusions can we make from data?
The cycle of collecting, presenting and analysing data usually involves translating data from one form to another, mathematical processing, graphical display and analysis; only then can we begin to draw conclusions. A set of repeat measurements can be processed to calculate a range within which the true value probably lies and to give a best estimate of the value (mean). Displaying data graphically can help to show trends or patterns, and to assess the spread of repeated measurements. Mathematical comparisons between results and statistical methods can help with further analysis.
1. present observations and other data using appropriate formats
2. when processing data use SI units where appropriate (e.g. kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate
3. when processing data use prefixes (e.g. tera, giga, mega, kilo, centi, milli, micro and nano) and powers of ten for orders of magnitude
4. be able to translate data from one form to another
5. when processing data interconvert units
6. when processing data use an appropriate number of significant figures
7. when displaying data graphically select an appropriate graphical form, use appropriate axes and scales, plot data points correctly, draw an appropriate line of best fit, and indicate uncertainty (e.g. range bars)
8. when analysing data identify patterns/trends, use statistics (range and mean) and obtain values from a line on a graph (including gradient, interpolation and extrapolation)
9. in a given context evaluate data in terms
of accuracy, precision, repeatability and reproducibility, identify potential
sources of random and systematic error, and discuss the decision to discard or
retain an outlier
11. in a given context interpret observations and other data (presented in diagrammatic, graphical, symbolic or numerical form) to make inferences and to draw reasoned conclusions, using appropriate scientific vocabulary and terminology to communicate the scientific rationale for findings and conclusions
12. explain the extent to which data increase or decrease confidence in a prediction or hypothesis
Chapter IaS3 How are scientific explanations developed?
Scientists often look for patterns in data as a means of identifying correlations that can suggest cause-effect links – for which an explanation might then be sought. The first step is to identify a correlation between a factor and an outcome. The factor may then be the cause, or one of the causes, of the outcome. In many situations, a factor may not always lead to the outcome, but increases the chance (or the risk) of it happening. In order to claim that the factor causes the outcome we need to identify a process or mechanism that might account for the observed correlation.
1. use ideas about correlation and cause to:
Scientific explanations and theories do not ‘emerge’ automatically from data, and are separate from the data. Proposing an explanation involves creative thinking. Collecting sufficient data from which to develop an explanation often relies on technological developments that enable new observations to be made. As more evidence becomes available, a hypothesis may be modified and may eventually become an accepted explanation or theory. A scientific theory is a general explanation that applies to a large number of situations or examples (perhaps to all possible ones), which has been tested and used successfully, and is widely accepted by scientists. A scientific explanation of a specific event or phenomenon is often based on applying a scientific theory to the situation in question.
2. describe and explain examples of scientific methods and theories that have developed over time and how theories have been modified when new evidence became available
3. describe in broad outline the ‘peer review’ process, in which new scientific claims are evaluated by other scientists
4. use a variety of models (including representational, spatial, descriptive, computational and mathematical models) to:
Chapter IaS4 How do science and technology impact society?
Science and technology provide people with
many things that they value, and which enhance their quality of life. However
some applications of science can have unintended and undesirable impacts on the
quality of life or the environment. Scientists can devise ways of reducing these
impacts and of using natural resources in a sustainable way (at the same rate as
they can be replaced). Everything we do carries a certain risk of accident or
harm. New technologies and processes can introduce new risks. The size of a risk
can be assessed by estimating its chance of occurring in a large sample, over a
given period of time.
1. describe and explain everyday examples and technological applications of science that have made significant positive differences to people’s lives
2. identify examples of risks that have arisen from a new scientific or technological advance
3. for a given situation: - identify risks and benefits to the different individuals and groups involved - discuss a course of action, taking account of who benefits and who takes the risks - suggest reasons for people’s willingness to accept the risk - distinguish between perceived and calculated risk
4. suggest reasons why different decisions on the same issue might be appropriate in view of differences in personal, social, economic or environmental context, and be able to make decisions based on the evaluation of evidence and arguments
5. distinguish questions that could in principle be answered using a scientific approach, from those that could not; where an ethical issue is involved clearly state what the issue is and summarise the different views that may be held
6. explain why scientists should communicate their work to a range of audiences.
OCR B GCSE Grade 9-1 Twenty First Century Science Suite
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