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GCSE PHYSICS: MOMENTUM

GCSE PHYSICS: MOMENTUM. By the end of this presentation you should be able to… Relate the force that acts on an object involved in a collision, to the change in its momentum. Recall and use Force = change in momentum time.

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GCSE PHYSICS: MOMENTUM

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  1. GCSE PHYSICS: MOMENTUM By the end of this presentation you should be able to… • Relate the force that acts on an object involved in a collision, to the change in its momentum. • Recall and use Force = change in momentum time

  2. The force on an object When two objects collide, they exert forces on each other while they are in contact. These forces will be equal but opposite to each other. Consider the force on one object involved in a collision. The force will be unbalanced, and will cause the speed and direction of the object to change. Perhaps even the objects shape.

  3. F = ma = rate of change of momentum Acceleration! (or deceleration) Now remember: momentum = mass x velocity Let us use u: to represent the initial velocity (ie before the collision), and v to represent the velocity the object has after the collision. The change in the momentum = (mv) - (mu) To see the effect this change has on the object, we need to consider how quickly it happens, so… The rate of change of momentum = mv – mu t Rearranging this gives m (v-u) = m x a = F = the force t applied on (or by) the object

  4. HOW IS THIS USEFUL? • To apply a large force, we need to allow the collision to happen almost instantaneously, where the object comes to rest very quickly. Like a hammer hitting a nail. Rubber mallets cannot exert forces as large as iron ones. Any object being hit by a rubber mallet will sink into the surface, reducing its speed slowly.

  5. HOW IS THIS USEFUL? 2. If we know a collision is likely between two objects (like during walking), we may want to reduce the forces to prevent pain. Wearing thick rubber soled shoes allows a runner to come to a stop slowly when each foot lands. Think about it, does it hurt more or less to run barefooted or with trainers on?

  6. HOW IS THIS USEFUL? 3. Air bags in a car, allow passengers to come to a slow stop and so avoids serious injury. Not wearing a seatbelt means that the dashboard of the car is the only thing that will stop you if the car collides with something (if there are no air bags). The force exerted to bring you from a high speed to rest will be large since you will be stopped very abruptly!

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