Forces & Motion Work

Work – force exerted on an object that causes it to move some distance Work = Force x Distance Force is still measured in Newtons Distance is measured in meters So…. the units for work are N٠m Instead of using the N٠m, we have a new unit called the Joule to measure work in.

Work In order for me to do work on an object, the object must move some distance as a result of my force. Example: A car is stuck in the snow and you exert a lot of force shoveling, pushing, and trying to get it to move. Since the car doesn’t end up moving, you haven’t done any work on the car!

Work In order for me to do work on an object, the force I exert must be in the same direction as the object’s motion. Example: Lifting a heavy box is work, but carrying the box to another location is not (even though it feels like it!) ForceMotion Force Motion

Calculating Work Which do you think involves more work: Exerting a force of 100 N to lift a potted tree 1 m off the ground or Exerting a force of 200 N to lift a heavier tree 1 m off the ground? Again, work = force x distance 100 N x 1 m = 100 J of work 200 N x 1 m = 200 J of work

Practice Problems To help rearrange the furniture in your classroom, you exert a force of 20 N to push a desk 10 m. How much work do you do? *work = 20 N x 10 m = 200 J A hydraulic lift exerts a force of 12,000 N to lift a car 2 m. How much work is done on the car? *work = 12,000 N x 2 m = 24,000 J

Practice Problems You exert a force of 0.2 N to lift a pencil off the floor. How much work do you do if you lift it 1.5 m? *work = 0.2 N x 1.5 m = 0.3 J Suppose an elevator lifted the previous tree 40 m still with a force of 100 N. How much work is the elevator doing? *work = 100 N x 40 m = 4,000 J