Module 4: Energy

Energy is defined as the capacity to do work. Energy takes many different forms and can be transformed from one form to another. Chemical, nuclear, thermal, radiant, potential and kinetic are common forms of energy. In every energy transformation, some energy is transferred to the environment in the form of heat.  Efficiency measures the percentage of energy that is effectively transferred.

Work is done when a component of force is applied in the direction of motion of an object.  Forces acting opposite the direction of motion do negative work.   The amount of work done by a force depends on the cosine of the angle between the force and displacement.  Power is the rate at which work is done.

Potential energy is the energy that an object has due to its position or shape.  Gravitational potential energy is equal to the amount of work done lifting an object against the force of gravity.  Objects in motion have kinetic energy, which is proportional to the mass of the object and the square of the speed.

Both work and energy are measured in Joules, and when work is done, energy is transformed. The amount of work done by the net force increases the kinetic energy of the object by an equal amount.

When work is done against a conservative force, the energy is stored for later use as potential energy.  Work done against non-conservative forces is transformed to thermal energy, increasing the heat of the surroundings.  Mechanical energy is the combination of potential and kinetic energy.  When only conservative forces do work, the total mechanical energy remains constant and is conserved.