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Give examples of interactions of objects at a distance without contact
Gravitational attraction, electrostatic attraction or repulsion, magnetic attraction or repulsion
Give examples of interactions of objects by contact
Normal contact force, friction
Explain terminal velocity in regards to a sky diver
Initially the skydiver has no air resistance and the only force acting on him is weight. As he falls, ha accelerates, increasing his speed. This makes air resistance increase so the resultant force decreases. Acceleration decreases as the force does (force=mass x acceleration), so he is not speeding up so quickly. Eventually, weight and air resistance are equal so there is no resultant force. There is no acceleration and a terminal velocity has been reached.
When can rotation occur?
If an object is attached to a pivot point. The force is applied to the object but not towards the point
Formula for a moment
Moment=force x distance from direction of force
What is the principle of moments when rotational forces are in equilibrium?
The sum of clockwise moments is equal to the sum of anti-clockwise moments
How do levers make use of moments?
They increase the perpendicular distance of the force from the pivot so decrease the force needed to produce the same moment - it becomes easier to lift things up
How do gears use rotation?
The first gear is supplying the force. If it is connected to a gear with fewer teeth, the second gear will turn faster but with less force and in the opposite direction to the first gear. If it is connected to a gear with more teeth, the second gear will turn slower but with more force and in the opposite direction
Note 
Flashcard (100)