P2 2 Forces

P2 2 Forces

Forces between objects
1. A force can change the shape of an object or change its motion or state of rest
2. The unit of force is the newton (N)
3. When two objects interact, they always exert equal and opposite forces on each other
  1. If object A exerts a force on object B, then object B exerts an equal force on object A in the opposite direction
Resultant force
1. The resultant force is a single force that has the same effect as all the forces acting on an object
2. If the resultant force on a stationary object is zero, the object will remain at rest
3. If the resultant force on a moving object is zero, the object will continue moving at the same speed in a straight line
4. If the resultant force on an object is not zero, the velocity of the object will change
  1. Remember, velocity means speed AND DIRECTION
5. If two forces act on an object along the same line, the resultant force is ...
  1. ... their sum if the forces act in the same direction
  2. ... their difference if the forces act in opposite directions
Force and acceleration
1. The bigger the resultant force on an object, the greater its acceleration
2. The greater the mass of an object, the smaller its acceleration for a given force
3. Resultant force (in newtons) = mass (in kilograms) x acceleration
  1. F = ma
On the road
1. Friction and air resistance oppose the driving force of a car
  1. "Oppose" means they act in the opposite direction
2. Stopping distance = thinking distance + braking distance
  1. Slow reaction time and high speed increase the thinking distance
    1. Slow reaction time can be caused by tiredness, alcohol or drugs
  2. High speed, poor weather conditions and poor maintenance increase the braking distance

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