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8.3 Moving About

8.3 Moving About. Focus 2: Acceleration and Force. Define Acceleration. Acceleration is positive if the object is speeding up Acceleration is negative if the object is slowing down or travelling in a “negative” direction or backwards. Newton’s Three Laws.

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8.3 Moving About

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  1. 8.3 Moving About Focus 2: Acceleration and Force

  2. Define Acceleration Acceleration is positive if the object is speeding up Acceleration is negative if the object is slowing down or travelling in a “negative” direction or backwards

  3. Newton’s Three Laws 1. An object remains at rest or travelling at constant velocity unless acted upon by an unbalanced force. 2. F = ma (the acceleration is proportional to the total force and inversely proportional to the mass of the object) 3. For every action there is an equal in magnitude and in the opposite direction paired reaction force.

  4. Mass and Weight • Mass is the amount of matter in an object. It is measured in kilograms (kg) • Weight is the force of gravity on an object. It is measured in Newtons (N) Weight Force

  5. Action of external forces • Accelerate an object • Decelerate an object • Change an object’s direction “a force causes an acceleration” • Change an object’s shape. • Friction and air resistance act to oppose motion i.e. slow an object down.

  6. Forces involved in causing a change in the velocity of a vehicle (“friction” includes air resistance ) Friction • Coasting with no pressure on the accelerator. • Pressing on the accelerator. Friction Force of engine Net force Net force

  7. Force of brakes Friction • Pressing on the brakes. • Passing over an icy patch on the road Net force No net force

  8. Force of brakes Force of engine Normal force Normal force weight weight • Climbing and descending hills • Note: this assumes the cars are accelerating in each case. Otherwise, there is no net force. Friction Friction Net force Net force

  9. Following a curve in the road Friction (centripetal force) Note that in this case,

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