# Review

Review the following tips and summary for this unit:

TIP: Work is a scalar quantity – no association with direction; all types of energy and energy transfer are scalar quantities.

TIP: Work is always DONE BY or DONE ON.

The work done by a constant force on an object is defined as the product of the component along the direction of displacement and the magnitude of the displacement.

W = (Fcos Θ) change in x

When work is done by a net force on an object and the only change in the object is its speed, the work done is equal to the change in the object’s kinetic energy. (THIS IS THE WORK-KINETIC ENERGY THEOREM)

Potential energy is always associated with a system of 2 or more interacting objects.

Law of Conservation of Energy – we can neither create nor destroy energy – energy is always conserved. If the total amount of energy in a system changes, it can only be due to the fact that energy has crossed the boundary of the system by a transfer mechanism.

Power is the time rate of energy transfer.

Average power = work/time

The watt represents the rate of energy transfer – the watt is the same as a joule/s.

The work done by a variable force acting on an object that undergoes a displacement is equal to the area under a graph of F x versus x.

The kinetic energy of an object of mass m moving with a speed v is defined as

KE = ½ mv2

The gravitational potential energy associated with an object of mass m that is elevated a distance of y above Earth’s surface is given by

PE = mgy

The elastic potential energy stored in a spring is given by

PEs = ½ kx 2

Average power is the ratio of energy transfer to the time interval during which the transfer occurs.

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