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(New page: {| width="500px" cellspacing="10px" align="center" border="1" | Image:fig a.GIF | valign="top"| Modelling the bike as a particle can provide an explanation for the fact that it moves ...)
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Revision as of 16:44, 8 April 2011
| Modelling the bike as a particle can provide an explanation for the fact that it moves backwards when pulled backwards.
Modelling an object as a particle is an idealisation (or abstraction) which can be useful in many cases. |
| Modelling the drum as a particle can explain what happens if the string is horizontal, but not what happens if the string is vertical.
Beware of potential problems when modelling objects as particles. |
| Write down a simple definition of a force in your own words. |
| Exploring the effects of gravity on objects can help create a definition of a force. |
| Gravity can change the motion of a ball in a number of ways. |
| A force is something that causes a change to the motion of a body. |
| Newton’s first two laws are based on an understanding of this idea of how a force changes motion. |
| In the first car the resultant force is in the direction of motion and the car gains speed.
In the second case the resultant force is zero and the car travels at a constant speed. In the third case the resultant force is backwards and the car slows down. |
| In the first case the resultant force is upwards. As the parachutist is also moving downwards, he slows down.
In the second case the resultant force is zero and the parachutist moves with a constant speed. |
| The resultant force is always downwards.
If the resultant force were zero at the highest point, the ball would stay there!! |
| No, the motion is changing from downwards to upwards.
The resultant force is upwards, for almost all of the time that the ball is in contact with the table. |
| The direction of the motion is always changing, so the forces are not in equilibrium. |
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