topic 9 - forces & their effects

• work done & power

  the energy transferred by a force. it depends on the size of the force and how far the force moved
• formula for work done

  work done = force x distance moved in forces direction

  e = f x d

  ( J ) ( N ) ( m )
• formula for power

  power = work done / time taken

  p = e / t

  ( W ) ( J ) ( s )
• free body force diagram

  a diagram of an object that shows all the forces acting on it and the sizes of the directions. the forces include : drag, lift, thrust and weight
• vector diagram

  graphical representations of vector quantities that show both the magnitude and direction of the force
• force vectors perpendicular

  when two forces act at right angles to each other, their resultant force is given by the pythagorean theorem : a^2 + b^2 = c^2
• lever

  a simple machine that consists of a rigid bar that rotates around a fixed point called a pivot
• gear

  a rotating wheel with teeth that interlock with another wheel with teeth. they are used to transmit rotational forces
• where are gears found ?

  -cars

  -bikes

  -children’s toys
• moments

  the turning effect of a force. it happens when you apply a force to something that can rotate around the pivot

  example : turning a door handle, pedals on a bicycle
• formula for moments

  moments = force x length

  ( NM ) ( N ) (m)
• principle of moments

  if an object is balanced the total clockwise moment = total anti-clockwise moment of the same point