Human reaction time

Question 1

What is human reaction time?

Answer 1

the time between a stimulus occurring and a response

Question 2

When driving, drivers have to react to change in traffic. What might their reaction time be affected by?

Answer 2

• tiredness
• alcohol and drugs
• distractions
• age

Question 3

What is a typical reaction time?

Answer 3

0.20 s to 0.25 s

Question 4

How can you measure human reaction time?

Answer 4

with the ruler drop test

reaction time = √((2 × distance ruler falls) ÷ gravitational field strength)

Question 5

A driver moving at 30 km/h in her car has a reaction time of 0.25 s. Calculate the distance the car travels before seeing a hazard in the road and then applying the brakes.

Answer 5

distance = speed × time

30 km/h = 30 000 m ÷ 3600 s = 8.3 m/s

distance travelled = 8.3 × 0.25 = 2.1 m

Question 6

Define human reaction time.

Answer 6

the time between a stimulus occurring and a response

Question 7

Give 3 factors that can cause human reaction time to increase.

Answer 7

• tiredness
• alcohol or drugs
• age
• distractions

Question 8

A ruler drop test is conducted five times with the same person. The results show that the five distances fallen are: 0.16 m, 0.17 m, 0.18 m, 0.16 m and 0.15 m.

(a) Calculate the mean distance that the ruler drops.
(b) Calculate the person’s reaction time.

Answer 8

(a) mean = (0.16 + 0.17 + 0.18 + 0.16 + 0.15) ÷ 5 = 0.16 m

(b) reaction time = √((2 × 0.16) ÷ 10) = 0.18 s

Question 9

Explain why the reaction time doubles when the distance that a ruler falls increases by a factor of 4.

Answer 9

Reaction time is proportional to the square root of the distance an object falls. The square root of 4 is 2, so four times the distance means twice the reaction time.