Forces and Free Body Force Diagrams

• Forces can be contact or non-contact:

  • For a contact force, the two objects must be touching e.g. pushing or pulling an object
  • Non-contact forces are forces between two objects that arent touching
• What is an interaction pair?

  An interaction pair refers to a pair of forces that act on two different objects in opposite directions.

  Example: If a person leans on a wall, they are pushing the wall and the wall pushes back on the person
• If a number of forces act towards a single object, you can replace them with a single force called a resultant force.

  It has a same effect on the motion of the object just as the original forces acting together
• The effect of forces decides whether the object accelerates, decelerates or has a steady speed
• Forces are vectors, so they have a size and direction. A free body diagram is a diagram of an object with arrows drawn to show the direction and size of the forces acting on the object
• An object with zero resultant force will either be stationary or moving at a steady speed
• If theres a non-zero resultant force on an object, it will rather accelerate or decelerate, because the forces are unbalanced