SITEMAP School-college Physics Notes: Forces & motion Section 2.5 Circular motion
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Forces and Motion 2.5 Forces and circular motion - including acceleration and centripetal force
Doc Brown's Physics exam study revision notes
2.5 Forces and circular motion - including acceleration and centripetal force
This section was adapted, re-edited and extended from the web page including a section on Gravity and circular motion.
circular motion - velocity & centripetal force
To keep a body moving in a circle there must be a force directing it towards the centre.
This is called the centripetal force and produces the continuous change in direction of circular motion.
Swinging something round on a string.
When you swing something round on the end of a string, the tension in the string is the centripetal force.
The centripetal force will vary with the mass of the object, the speed of the object and the radius of the path the object takes.
The same arguments on circular motion apply to the movements of planets around a sun, a moon around a planet and a satellite orbiting a planet. The orbits are usually elliptical, rarely a perfect circle, but the physics is the same.
In these cases, it is the force of gravitational attraction that provides the centripetal force and it acts at right angles to the direction of motion.
You should also realise that they are moving through empty space (vacuum), so there are no forces of friction to slow the object down.
This is why the planets keep going around the Sun and the moon keeps going around the Earth.
When satellites are put into orbit they are given just the right amount of horizontal velocity so that the resultant centripetal force of gravity keeps the satellite in its a circular orbit.
You can vary this horizontal velocity to position satellites at different distances above the Earth's surface.
Keywords, phrases and learning objectives for circular motion
orces involved in circular motion and the acceleration and centripetal force holding one object orbiting another in a gravitational field.
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