P2(i) - Forces and Motion 4.

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The Three Laws of Motion.

Around the time of the Great Plague in the 1660s, a man called Isaac Newton worked out the Three Laws of Motion.

First Law - Balanced Forces Mean No Change in Velocity.

So long as the forces on an object are all balanced, then it'll just stay still, or else if it's already moving it'll just carry on at the same velocity, so long as the forces are balanced.

1) When something is moving e.g. a car, at a constant velocity then the forces on it must all be balanced.

2) Things DO NOT need a constant overall force to keep them moving.

3) To keep going at a steady speed, there must be zero resultant force.

Second Law - A Resultant Force Means Acceleration.

If there is an unbalanced force, then the object will accelerate in that direction.

1) An unbalanced force will always produce acceleration (or deceleration). 

2) This "acceleration" can take five different forms: Starting, stopping, speeding up, slowing down and changing direction.

3) On a force diagram, the arrows will be unequal:

(http://www.physicstasks.eu/_upload/00382/auto_1_en.gif)

DON'T EVER SAY: "If something's moving there must be an overall resultant force acting on it."

This is not true. If there's an overall force it will always accelerate. you get steady speed from balanced forces.

Three Points:

1) The bigger the force, the greater the acceleration or deceleration.

2) The bigger the mass, the smaller the acceleration or deceleration.

3) To get…

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