# Forces and motion in a nutshell

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• Created on: 14-04-13 13:33

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IGCSE Forces and Motion in a nutshell Cross year test November 2012-nos 1-12
1. Be familiar with distance vs time graphs and know that gradient is speed.
2. Know that velocity is speed in a stated direction.
3. Know that acceleration = (v-u)/t ( change in speed divided by time taken)
4. Be familiar with speed vs time graphs. Know that area under gives distance travelled
5. Know that stopping distance = thinking distance + braking distance
6. Thinking distance is affected by alcohol/drugs, tiredness, alertness of driver.
7. Braking distance is affected by condition of brakes, grip of road surface, mass of
vehicle and initial speed of vehicle.
8. Identify various types of force (e.g. gravitational, electrostatic etc)
9. Know that Newton realised that forces changed the speed (or shape or direction) of
something. Recall and use F=ma in calculations about forces, masses and acceleration.
10. Know that Newton realised that there was a gravitational force between all masses
and that things fall because of the Earth's gravity giving them weight. Weight = mass
× g
11. Know that forces come in pairs. A cannot push B without A feeling the push as well.
12. Know that drag increases with speed and hence things have a maximum speed when
drag is equal to the driving force. Make sure you can apply this to the top speed of a
car AND to the terminal velocity of a parachutist.
13. A moment is the turning effect of a force pivot: moment = force × perpendicular
distance from pivot
14. The weight of a body acts through its centre of gravity, which can be found by
hanging up a shape from different places and drawing a vertical line beneath each
one
15. A stable objects has a low centre of gravity and a wide base area and is difficult to
topple over, an unstable object has a high centre of gravity and a narrow base area
and is easy to topple over
16. Springs and wires obey Hooke's law when stretched as extension is directly
proportional to load applied upto the elastic limit and so a graph of extension
against load is a straight line
17. Rubber bands do not obey Hooke's law and so a graph of extension against load is a
curve