Stopping distance and reaction time - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Stopping distance and reaction time

Forces

Lesson 17 of 20

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up

Forces

Lesson 17 of 20

Answer each one, then check.

1

What is speed?

2

What is distance = speed × time?

3

What is reaction time?

4

What does braking do?

5

What is a typical human reaction time?

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Forces

Lesson 17 of 20

1

What is speed?

Distance divided by time

2

What is distance = speed × time?

s = vt

3

What is reaction time?

The time between seeing something and reacting

4

What does braking do?

Reduces the vehicle's kinetic energy

5

What is a typical human reaction time?

0.2 s to 0.9 s

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Forces

Lesson 17 of 20

1

Define stopping distance, thinking distance and braking distance.

2

Explain how speed affects stopping distance.

3

Describe factors that affect reaction time, and methods used to measure it.

4

Interpret graphs relating speed to stopping distance.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Forces

Lesson 17 of 20

STOPPING DISTANCE

stopping distance = thinking distance + braking distance

Thinking distance is the distance travelled during the driver's reaction time. Braking distance is the distance travelled under the braking force. For a given braking force, the greater the speed, the greater the stopping distance.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Stopping Distance

Forces

Lesson 17 of 20

Thinking distance is proportional to speed; braking distance is not.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Reaction Time

Forces

Lesson 17 of 20

Typical values and factors.

Idea

Detail

Typical reaction time

0.2 s to 0.9 s

Increases with

Tiredness, drugs, alcohol, distractions such as a mobile phone

Thinking distance

s = vt: reaction time × speed

Measuring it

Ruler drop test: the distance the ruler falls gives the reaction time

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Thinking Distance

Forces

Lesson 17 of 20

A driver travelling at 15 m/s has a reaction time of 0.60 s. Calculate the thinking distance.

1

Write the equation

s = vt

2

Substitute

s = 15 × 0.60

3

Answer

s = 9.0 m

ANSWER

9.0 m

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Stopping Distance

Forces

Lesson 17 of 20

A car has a thinking distance of 9.0 m and a braking distance of 14 m. Calculate the stopping distance.

1

Add

9.0 + 14 = 23 m

ANSWER

23 m

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Measuring Reaction Time

Forces

Lesson 17 of 20

Describe the ruler drop method.

1

Set up

A partner holds a ruler vertically with the zero between your thumb and finger

2

Drop

Without warning they drop it, and you catch it as fast as you can

3

Measure

The distance fallen is read from the ruler

4

Convert

Use a table of distance against time, then repeat and find a mean

ANSWER

The longer the distance the ruler falls, the longer the reaction time.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Distractions

Forces

Lesson 17 of 20

Explain the effect of a driver texting on the stopping distance.

1

Reaction time

Increases

2

Thinking distance

s = vt is greater

3

Stopping distance

So the total stopping distance is greater

ANSWER

A longer reaction time gives a longer thinking distance and so a longer stopping distance.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Why It Matters

Forces

Lesson 17 of 20

Safety.

Speed limits

Higher speed means a much greater stopping distance.

Driver factors

Tiredness, alcohol, drugs and distractions raise reaction time.

Estimates

Estimate how emergency stopping distance varies over typical speeds.

Graphs

Interpret graphs of speed against stopping distance for different vehicles.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Key Terms

Forces

Lesson 17 of 20

Stopping distance

Thinking distance plus braking distance.

Thinking distance

Distance travelled in the driver's reaction time.

Braking distance

Distance travelled while the brakes slow the vehicle.

Reaction time

The time between a stimulus and a response.

Distraction

Something that takes a driver's attention away.

Mean

The average of repeated readings.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Forces

Lesson 17 of 20

YOUR TASK

Reaction Test

12 minutes

In a ruler drop test a student's three results for the distance fallen are 14 cm, 16 cm and 15 cm. Calculate the mean. Explain why a tired driver would have a longer stopping distance.

1

Find the mean.

2

Link to s = vt.

WHAT A GOOD ANSWER SHOWS

Mean = 15 cm. Tiredness increases reaction time, so thinking distance increases, increasing the stopping distance.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Can I...?

Forces

Lesson 17 of 20

Define stopping distance.

Define thinking and braking distance.

Use s = vt.

List factors affecting reaction time.

Describe a reaction-time test.

Read a stopping distance chart.

Explain the effect of speed.

Estimate stopping distances.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Summary & Exam Focus

Stopping = thinking + braking.

Thinking distance: s = vt.

Reaction time 0.2 to 0.9 s; increased by tiredness, drugs, alcohol, distractions.

Higher speed gives a greater stopping distance.

EXAM FOCUS

A driver travels at 15 m/s with a reaction time of 0.60 s. Calculate the thinking distance. (2 marks)

Multiply speed by reaction time.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Stopping distance and reaction time

Forces

Lesson 17 of 20

Answer all questions. Use the mark allocation as a guide to how much to write. · 16 minutes

Question 1 · 2 marks · Calculate

A car travels at 15 m/s. The driver's reaction time is 0.60 s. Calculate the thinking distance. Use the equation: distance = speed × time

Question 2 · 2 marks · State

Give two factors that can increase a driver's reaction time.

Question 3 · 4 marks · Use the chart

The chart shows the thinking distance and braking distance for a car at different speeds. (a) Use the chart to find the stopping distance…

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Stopping distance and reaction time (cont.)

Forces

Lesson 17 of 20

Question 4 · 3 marks · Explain

A driver is sending a text message while driving. Explain how this affects the stopping distance of the car.

Question 5 · 4 marks · Describe

Describe an experiment to measure a person's reaction time using a ruler. Explain how the result is used.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · 2 marks · Calculate

Forces

Lesson 17 of 20

“

A car travels at 15 m/s. The driver's reaction time is 0.60 s. Calculate the thinking distance. Use the equation: distance = speed × time

HOW TO ANSWER IT

Command word: Calculate. Worth 2 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · mark scheme

Forces

Lesson 17 of 20

2 marks available. Award a mark for each point made.

Correct substitution

1 mark

9.0 m

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · 2 marks · State

Forces

Lesson 17 of 20

“

Give two factors that can increase a driver's reaction time.

HOW TO ANSWER IT

Command word: State. Worth 2 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · mark scheme

Forces

Lesson 17 of 20

2 marks available. Award a mark for each point made.

First factor

1 mark

Second factor

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · 4 marks · Use the chart

Forces

Lesson 17 of 20

The chart shows the thinking distance and braking distance for a car at different speeds. (a) Use the chart to find the stopping distance at 50 mph. (b) Describe how the thinking distance changes with speed. (c) Explain why the braking distance increases more quickly than the thinking distance. (4 marks)

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · mark scheme

Forces

Lesson 17 of 20

4 marks available. Award a mark for each point made.

53 m

1 mark

Thinking distance increases steadily or proportionally

1 mark

Braking distance depends on kinetic energy

1 mark

Kinetic energy ∝ speed²

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · 3 marks · Explain

Forces

Lesson 17 of 20

“

A driver is sending a text message while driving. Explain how this affects the stopping distance of the car.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · mark scheme

Forces

Lesson 17 of 20

3 marks available. Award a mark for each point made.

Reaction time increases

1 mark

Thinking distance increases

1 mark

Stopping distance greater

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · 4 marks · Describe

Forces

Lesson 17 of 20

“

Describe an experiment to measure a person's reaction time using a ruler. Explain how the result is used.

HOW TO ANSWER IT

Command word: Describe. Worth 4 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · mark scheme

Forces

Lesson 17 of 20

4 marks available. Award a mark for each point made.

Ruler held and dropped without warning

1 mark

Distance fallen measured

1 mark

Converted to a reaction time

1 mark

Repeat and mean, compare conditions

1 mark

openrevise.com