ForcesForces

N Bronks

Distance, Speed and Time

Speed = distance (in metres)

time (in seconds)

D

TS

1) Dave walks 200 metres in 40 seconds. What is his speed?

2) Laura covers 2km in 1,000 seconds. What is her speed?

3) How long would it take to run 100 metres if you run at 10m/s?

4) Steve travels at 50m/s for 20s. How far does he go?

5) Susan drives her car at about 40m/s (136km/hr or 85mph). How long does it take her to drive 20km?

Distance-Time Graphs

D

t

1/.Constant Speed

D

t

2/.Stopped

D

t

3/.Faster Constant

Speed

Distance-time graphs

40

30

20

10

0

20 40 60 80 100

4) Diagonal line

downwards =

Back to Start

3) Steeper diagonal line =

Faster Speed

1) Diagonal line =

Constant Speed

2) Horizontal line =

Stops

Distance

(metres)

Time/s

40

30

20

10

020 40 60 80 100

1) What is the speed during the first 20 seconds?

2) How far is the object from the start after 60 seconds?

3) What is the speed during the last 40 seconds?

4) When was the object travelling the fastest?

Distance

(metres)

Time/s

Speed vs. Velocity

Speed is simply how fast you are travelling…

Velocity is “speed in a given direction”…

This car is travelling at a speed of 20m/s

This car is travelling at a velocity of 20m/s east

Distance-Time Graphs

D

t

acceleration

AccelerationV-U

TA

Acceleration = change in velocity (in m/s)

(in m/s2) time taken (in s)

1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration?

2) A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by?

3) A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take?

4) A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?

Velocity-Time Graphs

V

t1/.Constant Acceleration

V

t

2/.Constant Velocity

V

t

3/.Deceleration

Velocity-time graphs

80

60

40

20

010 20 30 40 50

Velocity

m/s

T/s

1) Upwards line =

Constant Acceleration

2) Horizontal line =

Constant Velocity

3) Shallow line =

Less Acceleration

4) Downward line =

Deceleration

80

60

40

20

0

1) How fast was the object going after 10 seconds?

2) What is the acceleration from 20 to 30 seconds?

3) What was the deceleration from 30 to 50s?

4) How far did the object travel altogether?

10 20 30 40 50

Velocity

m/s

T/s

v/m/s 0 2 4 6 8t/s 0 1 2 3 4

Force causes a body to change velocity

The unit is called the

Newton (N)A few types

of Forces

Magnetic Force

Tensile Forces

Friction happens when 2 bodies are in contact.

Friction

• Friction is the force that opposes motion of a body when it is in contact with another.

Friction happens when 2 bodies are in contact.

Lubrication reduces friction

Friction

1) What is friction?

2) Give 3 examples where it is annoying:

3) Give 3 examples where it is useful:

4) What effect does friction have on the surfaces?

Force and acceleration

If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:

Force (in N) = Mass (in kg) x Acceleration (in m/s2)

F

AM