1. Mechanical Work

2. work  the energy transferred to an object by a force applied over a measured distance  as the force or distance increases, so does the work W = FΔd  this equation applies when the force and the displacement are in the same direction (positive work)  work is measured in joules (J) which is equal to a Newton-metre (N  m)

3. problem  A store employee exerts a horizontal applied force of magnitude 44 N on a set of carts. How much work is done to push the carts 15 m? Express in joules and kilojoules.

4. negative work  if the force applied is in the opposite direction of the displacement  an example could be the force of kinetic friction resisting the motion of an object  the equation in this case is: W = -F k Δd

5. problem  A toboggan carrying two children (total mass 85 kg) glides to a stop in 21 m along a horizontal surface at the bottom of a hill. The coefficient of kinetic friction between the toboggan and the snow is 0.11. (a) Calculate the force of kinetic friction acting on the toboggan. (b) Calculate the work done by the force of kinetic friction.

6. total work  the total work done in a system can be calculated by adding together the work done in both directions  total work = sum of positive and negative work on the object  example: if the applied force is in one direction and frictional force acts in the opposite direction

7. problem  Curtis pushes a bowl of cereal along a level counter a distance of 1.3 m. What is the net work done on the bowl if Curtis pushes the bowl with a force of 4.5 N and the force of friction on the bowl is 2.8 N?

8. note  the work done by friction is changed to thermal energy (heat)  in most cases, friction causes waste energy the can be observed as an increase in temperature

9. graphing work  on a force-distance graph, force is on the y-axis and distance is on the x-axis  the area under the graph yields work constant (+) forcechanging force

10. zero work  an object might experience force, displacement or both and still no work is done  holding a heavy box on your shoulder  force with no displacement  a puck sliding on an air table  displacement with negligible force  a skater being held up by her partner as they glide  force and displacement are perpendicular not parallel

11. summary  work is the energy transferred by an applied force over a distance  if force and displacement are in the same direction, the work is a positive value  if force and displacement are in opposite directions, work done is a negative value  if force and displacement are perpendicular to each other, no work is done  work is a scalar quantity measured in joules (J)