UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 20/05/2023 [SEARCH]

Nervous system: 6. Simple physical response tests - investigating how fast is your reaction time!

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(6) Simple physical response tests - investigating how fast is your reaction time!

Copied and re-edited from Reaction times and vehicle stopping distances  gcse physics revision notes

Simple reaction time experiments

Your reaction time to a situation may be typically 0.2 to 0.8 seconds when fully alert. However your reaction time can be affected by  tiredness, feeling unwell, drugs, alcohol, in other words anything that affects the speed of your brain function.

You can conduct quite simple experiments to test your reaction time to a particular situation. However, since the reaction time is too short.

(i) Computer screen reaction test - responding as quickly as possible to something appearing on the screen.

In this situation, the computer software generates something up on the screen and your click the mouse or tap the keypad in response to the visual (or sound?) stimulus.

The computer automatically times your response by monitoring your contact with the keyboard or by clicking the mouse - its more accurate, especially as it can measure reaction times in milliseconds.

Computer generated stimuli give more accurate response reaction times than e.g. the dropped ruler experiment described in section (b) which potentially involves human error - computer experiments avoid the possibility of the person anticipating when the event is to happen e.g. reading the body language of someone dropping the ruler in experiment (b) described below.

I've quickly written an extremely simple computer programme to test your response to a X appearing on the screen.

Response time test: It probably only works on Microsoft platforms, and maybe not all of them?

Your anti-virus protection might query it, because it is a .exe file, but its written with compiled BBC BASIC and should not pose any threat. Unfortunately I never learned to write in a multi-platform professional computer programming language, but I'm not exactly short of website projects!

 

(ii) Catching a falling object test

Fraught with human error, but a bit of classroom fun!

You get someone to hold a ruler vertically, with thumb and first finger, above someone else's hand, who is ready to catch it with their thumb and first finger.

First image on the right. The ruler should be held at the top of the scale and steady hands from both people.

The catching person should have the middle of their thumb and finger adjacent to zero on the cm scale - squat down to make sure you are reading the scale horizontally.

Then, without warning, the person holding the ruler, lets go of it. The second person has to react as fast as possible and catch the dropped ruler between their thumb and first finger.

Second image on the right.

The longer the distance d, the slower your reaction time!

When caught, you then read how far the ruler as fallen by taking the reading, to the nearest centimetre, from where the middle of their thumb and finger are.

You repeat the experiment a number of times to get an average, but its not a particularly accurate experiment.

You need to have steady hands and not let the ruler wobble about or fall at an angle other than vertical.

Controlling variables - fair test criteria:

You should drop the ruler from the same height each time the experiment is performed.

You should also use the same ruler and the same hand to catch the ruler.

Use the same person/people dropping the ruler and catching it though, obviously, you can compare one person's results with another.

The slower your response time, the further the ruler falls before being caught.

You might repeat the experiment by having e.g.

having some background distractions - a group of people talking nearby, or somebody trying to engage you in conversation or music playing,

or taking a caffeinated drink like coffee or cola to act as a stimulant. - a drug that speeds up neural activity in the central nervous system.

 

Extension of experimental results

You can pool class results and produce a histogram of number of pupils versus equally spaced reaction times.

You can do the same thing with a computer screen test too.

You can investigate the effect of stimulant like caffeine in coffee.

i.e. do the test 10 times, have a rest, drink a cup of coffee and later repeat the test.

You should find that you a bit faster, a smaller response time because caffeine is a central nervous stimulant. It makes you more alert.

 

How to calculate the response time from your results

There is a simple formula you can use to calculate the actual reaction time (t in s) from the distance the ruler falls (d in m), under the acceleration due to gravity (a = 9.81 m/s2).

t = √(2d / a) =  √(2d / 9.81)

e.g. if the ruler falls 10 cm (0.10 m), reaction time = √(2 x 0.1 / 9.81) = √ = 0.14 s

Where does the reaction time formula come from?

Don't worry, you don't have to know this for either your GCSE/IGCSE biology or physics exams!, but here is the derivation for my own satisfaction and perhaps some keen students too?

KEY: a = acceleration (= g = 9.8 m/s2), u = initial velocity (m/s), v = final velocity (m/s), t = time (s), d = distance (m)

If a body is moving with an initial velocity of u and accelerates in a uniform manner (constant acceleration a),

the increase in velocity in a time is given by:  t = at.

Therefore the final velocity v after time t is given by

(equation 1) v = u + at

Now, if a body is moving with uniform acceleration its average velocity is equal to half of the sum of the initial velocity u and final velocity v.

average velocity = (u + v) / 2

but from equation (1), v = u + at, and substituting in the above equation gives

(equation 2) average velocity = (u + u + at) / 2 = u + Żat

Now the distance d, moved (displacement) = average velocity x time  (remember v =  ∆d /t)

so, d = (u + Żat) x t

and, multiplying out gives (3): d = ut + Żat2

now in the experiment, u = 0, so the equation simplifies to (4): d = Żat2

this can now be rearranged to give equation (5): t = √(2d / a)

which is the equation you can use to calculate your actual reaction time from how far the ruler fell before you stopped it.


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