BJU Physics Chapter 9

Conservative Forces

A force is conservative if either of the following conditions is true: • The motion can produce and store potential energy • The work done by the force on a system as it moves between any two points is independent of the path followed by the system

Non Conservative Forces

Energy is not stored as potential energy, but it is converted into other forms of mechanically unusable energy • Kinetic frictional forces • Internal resistance forces • Fluid drag

Kinetic Energy

Energy of motion

Potential Energy

Energy that an object possesses because of its position or condition. Results from work done against a force.

Gravitational Potential Energy

Energy that an object possesses because of its position with respect to other masses. • Lifting an object • Stretching/compressing a spring

Erg

The CGS unit of energy and work.

Joule

The SI unit of energy and work (MKS).

Energy

The ability to do work

Work (W)

The amount of energy required to move an object. The product of the component of force in the direction of an object's motion and the distance the object moves. Scalar quantity that can be be positive or negative. It is positive whenever theta is less than 90 degrees, zero when at 90 degrees, and negative when greater than 90.

Spring Constant

The constant in Hooke's law that describes how much force the spring exerts as its length changes, also called k.

Reference Point

The place from which change is measured. Chosen arbitrarily, but chosen to make solving problems easiest.

Power

The rate at which work is done.

Work Energy Theorem

The work done on an object is equal to the change in the object's energy.

Hooke's Law

Within the elastic limit of a material, force is directly proportional to the distance of extension or compression. Work done by the spring is always opposite the work done on the spring.