Forces

• Force:

  An interaction that causes an object to start moving or speed up, stop moving or slow down, change direction or change shape
• Types of forces:

  • push
  • pull
  • twist
• • Contact forces require physical contact between surfaces
  • Non-contact forces does not require physical contact/touch
• An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force
• Unbalanced forces are not equal and they cause the motion of an object to change
• Reaction force and gravitational force are a balanced pair of forces
• Fomula for pressure:

  Pressure = force/area

  N/m2 pascal (Pa)

  1N/m2 = 1Pa

  common: N/cm2
• Larger area - lower pressure (E.g. large tyre - the large area makes the pressure lower, so the vehicle is less likely to sink into the mud)

  Smaller area - higher pressure (E.g. sharp knife - the force you put on a knife is more concentrated over a smaller area)
• Friction is the force that opposes motion between any surfaces that are in contact
• Four types of friction:

  • static - the friction between two still objects resting on the surface
  • sliding - solids
  • rolling
  • fluid - gas & liquids