The Three Laws of Motion

Overview of the Three Laws of Motion

AQA Physics Revision Guide Pages 41-42

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  • Created by: jenny100
  • Created on: 17-05-12 08:56

First Law

Balanced Forces mean No Change in Velocity

  • As long as the force applied to an object is balanced then it'll stay still or the same velocity
  • To keep going at a steady speed there must be zero resultant force
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Second Law

A resultant force means acceleration

  • If there's an unbalanced force then the object will accelerate in that direction
  • Acceleration can take 5 different forms: starting, stopping, speeding up, slowing down & changing direction
  • On a force diagram the arrows will be unequal
  • The bigger the force the greater the acceleration or deceleration
  • the bigger the mass the smaller the acceleration
  • To get a big mass to accerate as fast as a small mass the force acting on it must be bigger

The Overall unbalanced force is often called the resultant force:

Force = Mass x acceleration

Resultant force is the larger force subtracted from the smaller force

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Third law - Reaction Forces

If object A exerts a force on object B then object B will exert the exact opposite force on object A

  • Basically if you push on a trolley it will push back just as hard
  • As soon as you stop pushing so does the trolley
  • When two skaters push against each other they feel the same size forces but in opposite directions so they'll accelerate away from each other. It depends on the mass of each skater as to which one accelerates away the fastest
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