Work Depends on force exerted on an object
Work Depends on: force exerted on an object and how far the object moves W = Fd For work to be done: must apply a force must MOVE the object must have force and displacement in the same direction Work affects an objects energy!
Work Pushing this car is work because F and d are in the same direction Why aren’t the following tasks considered work? A student holds a heavy chair at arm’s length for several minutes. A student carries a bucket of water along a horizontal path while walking at a constant velocity.
Work How would you calculate the work in this case? What is the component of F in the direction of d? F cos If the angle is 90°, what is the component of F in the direction of d? F cos 90° = 0 If the angle is 0°, what is the component of F in the direction of d? F cos 0° = F
Work
Work is a Scalar Work can be positive or negative but does not have a direction.
Kinetic Energy What are the SI units for KE? kg • m 2/s 2 or N • m or J
Work and Kinetic Energy KE is the work an object can do if the speed changes. Wnet is positive if the speed increases.
Potential Energy associated with an object’s potential to move due to an interaction with its environment A book held above the desk An arrow ready to be released from the bow Some types of PE are listed below. Gravitational Elastic Electromagnetic
Gravitational Potential Energy What are the SI units? kg • m 2/s 2 or N • m or J The height (h) depends on the “zero level” chosen where PEg = 0
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