Topic 9 - Forces and their effects

• Interaction at a Distance:

  • Gravitational Field: Earth attracting an apple.
  • Electrostatic Field: Charged objects repelling/attracting.
  • Magnetic Field: Magnets attracting/repelling.
• Interaction by Contact:

  • Normal Contact Force: Book resting on a table.
  • Friction: Sliding a box across a floor.
• How do you draw vectors?

  1. Draw all the forces acting on an object, to scale, 'tip-to-tail'. 2)Then draw a straight line from the start of the first force to the end of the last force — this is the resultant (or net) force. 3)Measure the length of the resultant force on the diagram to find the magnitude of the force and the angle to find its direction.
• What is the formula for the moment of force?

  moment of force = Force * distance.
• What is the formula for the sum of clockwise moments?

  Sum of clockwise moments = the sum of anticlockwise moments.
• You can reduce unwanted energy transfer by lubricating hinges to reduce friction.