9K Speeding Up...How forces affects speed
lesson
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Forces and the effects of forces
Forces cannot be directly observed, but the effects of a force can. A force measured in
Newtons exerted on an object can result in many different resultant actions. Forces affect
the way objects move. You cannot see a force that changes an objects speed or direction.
A car accelerates forwards due the force exerted by the car’s engine on the front wheels. If
you continue to accelerate, the car will achieve its maximum top speed, where the force of
the engine is equal to the force of internal resistance and air resistance. If you apply a
breaking force the car will slow to a stop Why do fast cars have the best brakes fitted ?
Speed, velocity, acceleration and deceleration:
Speed Velocity Acceleration Deceleration
Diagram
Units ms-1 ms-1 (0 to 3600) m/s2 -m/s2
Notes Speed describes the distance Acceleration describes the change of Deceleration is the
travelled by an object and the time velocity and the time taken for that change in velocity
taken. Velocity describes the change to occur. Constant when objects slow
distance travelled and the time acceleration gives a straight line, down. It always
taken, but it also describes the whereas changing acceleration gives has a negative
direction of travel. a curved line on velocity time graphs. value.

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Speed one
The speed of a moving object describes the distance travelled in metres over time in
seconds. Knowing the speed of an object allows you to calculate, how long it will take
the moving object to cover a certain distance. Calculating the speed in metres per
second (ms-1) of an object is simple using the following formula:
Distance travelled (m)
Units for speed = ms-1
Speed =
Time taken (s)
Calculating speed:
Lorry Sports car Cyclist Sprinter
Diagram
Distance (m) 2000m 2000m 2000m 2000m
Time taken (s) 150s 60s 200s 400s
Speed (ms-1) _____________ ? _____________ ? _____________ ? _____________ ?
Notes Using the equation above, work out the speed of the lorry, sports car, cyclist and sprinter. Also
calculate how long in time, it would take each object to cover 10km (10,000m)

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Speed two
Distance time graphs show distance travelled over time. The graph below shows a bus journey:
The bus left the depot and took 200 seconds to travel 150 metres to a set of traffic lights. The bus
waited here for 200 seconds while the lights changed to green. The bus then took a further 50
seconds to travel 100 metres. It then took 200 seconds to travel 50 metres and then a further 100
seconds to travel a further 100 metres. It then stopped back at the bust station. The total time for
the journey was 750 seconds with the total distance covered being 400 metres.
Distance time graphs:
Displaying the bus journey using distance time graphs
F
Diagram
400 E
Distance travelled (m)
350
D
300
250 C
B
200
150
A
100
50
0
0 100 200 300 400 500 600 700 800
Time taken (s)
Table Distance travelled (m) 0 150 150 250 300 400 400
Time taken (s) 0 200 400 450 650 750 800
Notes Calculate the following from the above information: (a) Work out the average speed for the entire
bus journey. (b) At what point was the bus travelling at its fastest speed (c) At what point was the
bus travelling at its slowest speed. (d) For how many seconds in total was the bus at rest.

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Speed three
Using distance time graphs, you can see that the steeper the slope, the greater the object’s
speed. We can use the gradient of the slope to calculate the speed of the moving object:
Change in y (distance)
Units for speed = ms-1
Speed = Gradient of distance time graph Gradient =
Change in x (time)
Using the graph, the speed at point C is worked out by dividing the distance travelled
(250m...change in y) by the time taken (250s...change in x) This gives a speed or gradient
of 1ms-1.
Speed and gradients:
Distance time graph Distance time graphs
A B
D
distance (m)
distance (m)
400
350
Distance travelled (m)
C
300
250m
250
200 B time (s) time (s)
150 C D
A 250s
100
distance (m)
distance (m)
50
0
0 100 200 300 400 500 600 700 800
Time taken (s)
time (s)
time (s)
Calculate the following from the information given above: (a) Work out speed or gradient of the
object at points A and B. (b) Work out the total distance travelled. (c) Work out the average
speed of the moving object over the 700 seconds. (d) Which graphs (A, B, C or D) shows an
object with (i) the lowest speed (ii) the highest speed (iii) zero speed.

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Using distance time graphs
Using distance time graphs is simple. The information provided by the graph, tells us the
speed or velocity of the moving object and the total distanced travelled over time. You can
see that the steeper the slope, the greater the object’s speed. We can use the gradient of
the slope to calculate the speed of the object. Also the total distance travelled by the
moving object can be determined by using the distance time graph.
Using distance time graphs:
Distance time graph Questions
Question Answer
B
A
400
Which objects are not moving at all at the
end ?
300
Which object is moving at the fastest
Distance travelled (m)
speed at the end ?
C
200 Which object took 800 seconds to travel
400 metres. Calculate its average speed.
100 Which object stops moving after 300
D seconds ?
0 Which object travels the least distance.
0 100 200 300 400 500 600 700 800
Calculate its average speed ?
Time taken (s)
Remember the following equation:
Change in y (distance)
Units for speed = ms -1
Speed = Gradient of distance time graph Gradient =
Change in x (time)

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Velocity
The speed of an object tells us how fast an object moves (distance travelled over time
taken), whereas using velocity tells us the speed of an object and the direction it is
travelling. The direction of an object can be given quite simply as towards or away
from us, or as a bearing having a value from 0 to 360 degrees.
Distance travelled (m)
Units for velocity = ms-1 (0 to 360o)
Velocity = + Direction (0 to 360o)
Time taken (s)
Velocity:
Motorway traffic Coming towards you Going away from you
Diagram
Notes Motorway traffic is a good A sports car that is coming A sports car that is going
example of how using velocity toward you at very high away from you at very high
gives us more information than
velocity may cause you to velocity would cause you no
speed. In the fast lane, in both
move out of its path. How anxiety at all. How would you
directions the speed is the
would you say ‘towards you’ say ‘away from you’ using
same at 70mph, but the
using degrees (0 to 3600) ? degrees (0 to 3600) ?
direction is opposite.