1. Speed up an object
  2. Slow down or stop an object
  3. Change the direction of an object
  4. Change the shape of an object


  1. The roughness of the surfaces (e.g. stepping on banana peel compared with carpet)
  2. The force pushing the surfaces together (e.g. A heavy truck's tyres compared with a bicycle's tyres on the road)
  3. Whether the surfaces are moving or stopped

  1. Static Friction - acting between 2 stationary bodies (e.g. holding a person on a chair)
  2. Sliding Friction - acting between surfaces where one is moving (e.g. sliding furniture across the floor, writing with a pencil on paper)
  3. Rolling Friction - acting between surfaces of objects where one has a rounded shape (e.g. car tyres on the road, ball bearings); less than sliding friction

  1. Reducing the force pushing both surfaces together
  2. Using a lubricant such as oil or water between the surfaces
  3. Using ball bearings or rollers between both surfaces
  4. Polishing both surfaces

The Force Rule

  1. An object of greater mass has a greater force (e.g. An adult baseballer will hit the ball further than a child)
  2. An object with greater acceleration has a greater force (e.g. A faster karate expert can strike with greater force than a slower person)
Force (newtons) = Mass (kilograms) × Acceleration (metre per second-squared)
F = m × m/s2
F = m × a
F = ma

Answer:F = ma
= m × a
= 100 × 5
= 500 N (newtons)

Force of Gravity

Weight (newtons) = Mass (kilograms) × Gravitational Acceleration (9.8 m/s2)
W = m × g