2 Velocity and acceleration

21 April 2023

Carriageways Cars Vans

Local roads

Single carriageway

Dual carriageway

Motorways

towing a trailer

Know your limit!What are the UK speed limits for cars and vans?

Vans between 2000kg and 7500kg.

2 Velocity and acceleration

21 April 2023

Carriageways Cars Vans

Local roads As marked As marked

Single carriageway roads

60 50

Dual carriageway roads 70 60

Motorways 70 * 70 *

towing a trailer * 60 * 60

Know your limit!Why do you think vans are

lower unless they weigh under 2000kg?

2 Velocity and acceleration• What is the difference between speed and

acceleration?• What is acceleration and what are its units?• What is deceleration?

21 April 2023

Motorways and dual carriageways have a central barrier and higher maximum speeds. Why is this safer than a single carriageway at 60mph?

World RecordsUsain Bolt is the 100m world record holder. Time = 9.58 seconds.

What was his average speed for this distance?

Speed =

Why was this the average speed?

What condition(s) would have to be met to make a valid record?

World RecordsUsain Bolt is the 100m world record holder. Time = 9.58 seconds.

What was his average speed for this distance?

Speed = distance = 100m = 10.44 m/s time 9.58s

Starts at zero and he takes time to reach his maximum speed.

Wind speed

Track distance

Timing system

Velocity = speed in a given direction

On a treadmill a speed is set. The belt runs at the speed set. E.g. 3 m/s

How fast is the runner running (speed)?

How quickly do they move in the direction they are running (velocity)?

Velocity tells us how quickly we are travelling in the direction we want to go.

DirectionVelocity tells us how quickly we are travelling in the direction we want to go.

If we wanted to travel from Nottingham to Donington the A52 is the most direct route.Distance = 48 miles.Time = 1 hour.

However, travelling due East is shorter: 40 miles.

What is the speed for this journey?

What is the velocity due East?

DirectionVelocity tells us how quickly we are travelling in the direction we want to go.

If we wanted to travel from Nottingham to Donington the A52 is the most direct route.Distance = 48 miles.Time = 1 hour.

However, travelling due East is shorter: 40 miles.

Average speed for this journey = 48 mph

Velocity due East = 40 mph East!

Movement in a circleIf an object moves in a circle at a constant speed of 10m/s what is its velocity?

A

B

C

D

Speed (m/s)

Velocity (m/s)

A 10

B

C +10

D 10 +

Movement in a circle

A

B

C

D

Speed (m/s)

Velocity (m/s)

A 10 -10

B 10 0

C 10 +10

D 10 0

+

Acceleration = Change in velocity per second

Acceleration = change in velocity (m/s)(m/s2) Time taken (s)

E.g. Rita Queen of speed accelerates from 0 to 30 m/s in 3 seconds. What is its acceleration in m/s2?

How can an object accelerate if its speed is constant?

Summary

• Velocity is speed in a given direction.• Acceleration is the change of velocity per

second.• An object travelling at a constant speed is

accelerating if its direction is changing.

Velocity = speed in a given direction

• On a trip across the Atlantic a plane takes 1 hour longer going west than going east.

• The air speed is the same for both trips. Why the difference?

New York London

7 hours

8 hours

Velocity = speed in a given direction

New York London

7 hours

8 hours

Air speed 540mph

Air speed 540mph

Wind 60mph

Velocity = 600mph

Wind 60mph

Velocity = 480mph