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.
See
An introduction
to the nervous system including the reflex arc (GCSE
level biology notes)
You can conduct quite simple experiments to test your
reaction time to a particular situation. However, since the reaction time is
too short, a stopwatch is no good, but there are ways of measuring your
reaction time indirectly by making other measurements from which you can
calculate your reaction time.
(a)
Computer screen test - where you respond as quickly as possible to
something appearing on the screen.
In this situation, the computer
software generates something up on the screen and automatically times
your response by monitoring your contact with the keyboard or by
clicking the mouse.
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!
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, 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. You
should also use the same ruler and the same people dropping the ruler
and catching it (fair test criteria), 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 some background distractions - a group of people
talking nearby, or somebody trying to engage you in conversation or
music.
Follow-up question on response
time
You can then do some 'nifty'
calculations to actually obtain a real response time - so you
using indirect data to get the response time.
It involves a two stage calculation
(at the highest GCSE level !!!).
Suppose the ruler is caught after an
average fall of 25 cm.
(i) You use the equation v2
- u2 = 2ad,
to calculate the final velocity (more
calculations using this equation)
v = final velocity (m/s), u =
initial velocity (m/s) = 0, a = acceleration = 9.8 m/s2
(gravitational field acceleration constant),
and d = distance fallen (m)
before catching the ruler.
Since u = 0 and d = 25/100 = 0.25
m
v2 - 0 = 2 x 9.8 x
0.25 = 4.9
v = √4.9 = 2.214 m/s (its
not this accurate, but we'll leave the s.f. decision until the end)
(ii) We can now use the acceleration
formula to calculate the response time.
a = ∆v / ∆t,
where a = acceleration (9.8 m/s2), ∆v = change in
velocity (m/s) and ∆t = response time
Therefore :
9.8 = 2.214 /
∆t, ∆t = 2.214 / 9.8 =
0.23 s
(2 s.f.)
So, on
average, the response time was about a quarter of a second.
(b)
