Kinematics

1. Kinematics Falling under the influence of gravity

3. Falling under the influence of gravity The ‘Guinea and Feather’ This experiment (also done on the moon) compares a light and a heavy object, falling under the influence of gravity in a vacuum. It proves that… In a vacuum on the surface of Earth, all objects fall with the same acceleration, g=9.81ms-2.

4. Determining the acceleration due to gravity • A falling body conforms to the criteria set for the application of the equations of motion. i.e. • It travels in a straight line • it has constant acceleration • If we measure the time (t) for a ball to fall a distance (s), starting from rest (u=0), we can determine its acceleration using… • Using this relationship, what graph could we plot to determine g? s = ut + ½ at2 which becomes… s = ½ gt2

5. Vertical Projection The equations of motion can be applied to bodies moving vertically under gravities influence: Question First watch this video. Now, analyse the video to determine… - fall time - height of cliff - velocity upon impact

6. An elephant and a feather are thrown out of a school building: • What is different about their resulting motion? • Why does their motion differ?

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8. Air Resistance and Terminal Velocity • ( Terminal velocity link – base jumping ) • A falling body experiences two main forces: • air resistance • weight • Weight will not change, however air resistance depends upon: • surface area • speed • For the falling body to stop accelerating, the weight and air resistance must be equal, causing the resultant force to be zero.

9. E.g. Skydiver Situation diagram: Free body force diagram:

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