Reaction times – how fast are yours? (Version 2.2)
Mic Porter – Ergonomist, School of Design, Northumbria University
Required
 Two people – both wearing shoes
 A 30cm ruler plastic or wooden, not metal as it can injure!
Task
 One person holds the ruler near the 30cm mark and lets it dangle vertically
downwards.
 The second person puts their thumb and forefinger either side of the ruler with the
zero just visible above the finger. Neither finger nor thumb must touch the ruler.
 Without warning (and after a pseudo random period of time) the first person releases
the ruler and the second tries to catch it between finger and thumb.
 Record the level (in cm) just above the finger and thus how far the ruler fell.
 Repeat 5 times and calculate the mean drop.
 Now swap roles; whose reaction time was shortest?
A little Ergonomics/Psychology
The sequence of events can be described thus. The eye must detect the ruler moving (or
perhaps the holding hand opening) and visual the information sent to the brain via the visual
cortex. The brain must then interpret the signals and determine the response that is to be
made and how to make action it. After the decision is made messages are sent, via the
nervous system, to the finger muscles ordering the actions to occur and the fingers move to
close about the ruler. When contact is made the message is sent back to the brain that the
action is complete. A typical hand-eye co-ordination task is complete.
The speed of messages along the “visual” and “motor” nervous system vary little but are
distance dependant so messages to and from the feet take longer than to and from the hand.
With training you can, however, improve the decision making “cognition” speed and the
latency of the muscles as they respond to the triggering signal.
A little secondary school physics (supplementary, non-essential)
The equation that relates the distance travelled (S), the initial velocity (U), the acceleration
(a) and the time(t) is S= Ut + 0.5at2. In this experiment the initial velocity is zero, the
acceleration is gravity (nominally 9.81MS-2) and the reaction time is to be determined.
Interpreting the results
Drop (cm), reaction time (milliseconds (1/1000s of a second)) (rounded) conversion table
Drop
(cm)
1
3
5
7
9
11
13
15
17
19
21
23
25
27
28
30
Reaction Time Drop Reaction Time
Comment
(milliseconds) (cm) (milliseconds)
45
2
65
Amazing – clairvoyant or cheating?
80
4
90
Impressive – do you play squash,
100
6
110
computer games, “chicken” when
crossing the road or fly jet fighters?
120
8
130
135
10
140
Excellent – what hand/eye co-ordination
150
12
155
games do you play? Squash? Tennis?
160
14
170
Cricket?
175
16
180
185
18
190
Good – but you could be better!
195
20
200
205
22
210
215
24
220
Average – not bad, just what is
expected (especially as you get older)!
225
26
230
235
240
29
245
Fair – Concentrate, pay attention; could
you be faster?
250
Whoops, rather too slow – hopefully the ruler missed your feet!
© Mic Porter
Additional experiments
 Dominant (prefered) hand verses non-dominant. Which hand is faster for you?
 Is “catching” between thumb and the other fingers slower than between thumb and
forefinger? Yes?
 Does age make a difference? Try children and “aged” adults; are the older slower?
 Tired (late at night) verses alert (early morning); does it make a difference? Of course!
 Experienced adults only! Does drinking alcohol slow down reaction times? Yes and
at much lower concentrations than the UK drink/drive limit of 80 milligrams of alcohol
per 100 millilitres of blood!1
How far will be travelled in a few milliseconds?
Velocity
20 (32)
Metres
per
second
8.9
30 (48)
mph (kph)
The Wright Bros. Flyer
cruising.
Further examples:
Cricket, county level fast
bowler.
Test cricket’s fastest
bowlers/Squash ball2.
Fastest UK mainline
train.
Fastest regular
commercial train (China).
Water bourn craft, world
speed record3
Land speed record for
motorbikes4.
Red Arrows at display
speed (Hawk trainer)
A 747 airliner cruising.
Wheeled vehicle, world
land speed record5.
A Euro-fighter
(Typhoon). (Mach 2.0)
An AK-47 Bullet muzzle
velocity.
The International Space
Station (ISS) orbiting.
An Apollo space craft
returning to earth
(maximum at re-entry)
Distance (Metres) travelled in milliseconds
100
150
200
250
300
0.9
1.3
1.8
2.2
2.7
13.3
1.3
2.0
2.7
3.4
4.0
40 (64)
50 (80)
60 (97)
70 (113)
80 (129)
17.9
22.4
26.7
31.3
35.8
1.8
2.2
2.7
3.1
3.6
2.7
3.4
4.0
4.7
5.4
3.6
4.5
5.3
6.3
7.2
4.5
5.6
6.7
7.8
8.9
5.4
6.7
8.0
9.4
10.7
100 (161)
44.7
4.5
6.7
8.9
11.2
13.4
125 (201)
55.9
5.6
8.4
11.2
14.0
16.8
140 (225)
62.6
6.3
9.4
12.5
15.6
18.8
217 (303)
135.5
13.5
20.3
27.1
33.9
40.6
317 (510)
141.7
14.2
21.3
28.3
35.4
42.5
376 (605)
168.1
16.8
25.2
33.6
42.0
50.4
415 (668)
186
18.6
27.8
37.1
46.4
55.7
560 (901)
250.3
25.0
37.6
50.18
62.6
75.1
760 (1223)
625.9
62.6
93.9
125.2
156.5
187.8
1500 (2414)
670
67.1
100.6
134.1
167.6
201.2
1745 (2808)
780.1
78.0
117.0
156.0
195.0
234.0
17500 (28163)
7823.2
782.3
1174
1565
1956
2347
1117.6
1676
2235
2794
3353
25000 (40234)
11176
1
The UK limit for car driving with alcohol in the blood is one of the least restrictive in the world;
Wikipedia has an outline of the background science and country comparisons at:
http://en.wikipedia.org/wiki/Blood_alcohol_content. [last accessed 02.11.14]
2 Just less than 4468 Mallard’s steam hauled speed record of 126mph set on Stoke Bank on 3rd July
1938. http://en.wikipedia.org/wiki/LNER_Class_A4_4468_Mallard [last accessed 02.11.14]
3 Held by Ken Warby driving Spirit of Australia at Blowering Damon on the 8th October 1978.
4 Held by Rocky Robinson riding Top Oil-Ack Attack streamliner (Suzuki Twin 2600 cc) at Bonneville,
on the 25th September 2010
5 Held by Andy Green driving ThrustSSC (Turbofan powered) in the Black Rock Desert on 15 th
October 1997. This is close to the speed of sound (at 20C) which is usually taken as 667mph, ie Mach
1.0)
© Mic Porter
106754488 (08/03/2016)