What effects how quickly a car stops?

Aims:

To understand that stopping distances are related to friction and speed

To understand what speed is and how it is measured

To be able to interpret distance/time graphs

Speed and stopping

Speed tells you how far you go in a certain time

The speed of a car affects how long it takes to stop The faster you are going, the longer it takes to stop

Thinking time = the distance you travel whilst THINKING about stopping

Braking distance = the distance you travel once you start to BRAKE

Stopping a car…

Braking distance

Too much alcohol

Thinking distance

Tiredness

Too many drugs

Wet roads

Driving too fast

Tyres/brakes worn out

Icy roads

Poor visibility

Distance-time graphs

40

30

20

10

0 20 40 60 80 100

4) Diagonal line

downwards =

3) Steeper diagonal line =1) Diagonal line =

2) Horizontal line =

Distance

(metres)

Time/s

40

30

20

10

0 20 40 60 80 100

1) How far had the object gone after 20 seconds?

2) How far had the object gone after 60 seconds?

3) When is the object standing still?

4) When was the object travelling the fastest?

Distance

(metres)

Time/s

Activity 1 : Complete the worksheet (10 minutes)

Activity 2

How could we compare the speeds of a car on two different surfaces

(The pink box on page 23 spotlight 8 may help)

© Boardworks Ltd 2003

Use this equation:

SPEED = distance

time

Speed is measured in many different units, e.g. m/s, km/h, km/s, miles per hour.The units of distance and time used will give the units to be used for speed.

d

s x t

Formula triangle

Formula triangle for measuring speed

© Boardworks Ltd 2003

Formula triangle

© Boardworks Ltd 2003

A boy travels from his home to the cinema, a distance of 10 km in 1 hour. Calculate his speed in km/h.

Examples

Speed in km/h =

d

s x t

Cover the quantity you want to calculate - s (speed)

d (distance in km)

t (time in h)

10 km

1 h=

= 10 km/h

Work out the speed of the two cars which is the fastest?

Complete the table on page 22 spotlight 8

then complete questions 1 to 5 on page 23.

0500

10001500200025003000

0 10 20 30 40

Met

ers

minutes

MY SCHOOL JOURNEY

1. How long did the journey take? 2. What was the total distance covered? 3. What was the average speed for the journey? 4. What was the average speed for the first 20 minutes and the last 20

minutes of the journey? Write a short story about this journey. What is happening in each 10 minute

segment? (Finish for homework)