## An Overview of the Important Concepts

## Work done

_

On the diagram, the motion is horizontally to the left, but the force is exerted with an angle. So we need to resolve the force. The horizontal component of the force is Fcosθ.

Thus, W=Fcosθ d, when there is an angle between the motion and the force exerted.

Work is measured in Nm, or J.

N = kg * m / s / s

Nm = kg * (m / s)^2

**Work done**on an object is the product of the magnitude of the displacement times the component of the force parallel to the displacement. W = FdOn the diagram, the motion is horizontally to the left, but the force is exerted with an angle. So we need to resolve the force. The horizontal component of the force is Fcosθ.

Thus, W=Fcosθ d, when there is an angle between the motion and the force exerted.

Work is measured in Nm, or J.

N = kg * m / s / s

Nm = kg * (m / s)^2

_ --------------------------------------------------------------------------------------------------------------------------------------------------------------

## _Kinetic Energy

The net work done on an object is equal to the change in
the object’s kinetic energy.

So it seems that work can also be obtained by the multiplying mass and velocity squared.

In fact, kinetic energy is equal to 1/ 2 mv^2. Here’s how it is derived.

So it seems that work can also be obtained by the multiplying mass and velocity squared.

In fact, kinetic energy is equal to 1/ 2 mv^2. Here’s how it is derived.

_ --------------------------------------------------------------------------------------------------------------------------------------------------------------

## Gravitational Potential Energy

_
There are two kinds of potential energy that we need to
know in this chapter: gravitational and elastic potential energy.

PEgrav = mgh

Gravitational potential energy is due to Earth’s gravity.

If we look at the units, PE = kg * m / s / s * m = kg * (m / s)^2, which is consistent with the unit of kinetic above.

PEgrav = mgh

Gravitational potential energy is due to Earth’s gravity.

If we look at the units, PE = kg * m / s / s * m = kg * (m / s)^2, which is consistent with the unit of kinetic above.

_ --------------------------------------------------------------------------------------------------------------------------------------------------------------

## Elastic Potential Energy

_
k is the string
constant, with the unit N/m. So it indicates how much force it can produce in a
unit of distance.

k * x is force. And if you were to graph force vs. x. The area under the linear graph is energy.

If we look at the units, PE = N/m * m^2 = Nm, which is consistent with the unit of work done above.

k * x is force. And if you were to graph force vs. x. The area under the linear graph is energy.

If we look at the units, PE = N/m * m^2 = Nm, which is consistent with the unit of work done above.

## Conservation of Mechanical Energy

## _Roller coaster question

When you see such a diagram, or even a more complicated one, do not fear. In the AP Exam, there is no air resistance or friction on the roller coaster question, so the only thing you need to look at is the height. It doesn't matter how curvy and complicated the roller coaster looks, when you are asked to find velocity at a certain point, think about the conservation of mechanical energy, and calculate the height difference (GPE difference).

## Power

_
Power is the rate at
which work is done. So it is just work divided by time. The unit is J/s, or W
(watt).

One horsepower is defined as 550ft lb / s, which is equivalent to 746 W.

One horsepower is defined as 550ft lb / s, which is equivalent to 746 W.

## Efficiency

Paragraph. 单击此处进行编辑.