Energy Unit Overview and Objectives

by: Patrick Cho, Matthew Meinzer, and Daniel Roe

Energy is the ability to produce a change in itself or its surroundings. It is measured in Joules (J). There are several types of energy such as: mechanical energy which is the sum of potential and kinetic energy, thermal energy, chemical energy, electrical energy, sound energy, etc. When there is a change in energy, there is work being done. Work is the measure of change in energy in an object. It can also be measured as Force (N) times the displacement (m).

Gravitational potential energy is the change of energy of an object when moved in a gravitational field. As an object gets higher from another relative object, its potential energy increases. The basic equation to find gravitational potential energy is: Ep = mgh.
Ep is the potential energy, m is the mass measured in kg, g is the acceleration due to gravity, and h is the change in height.

Example Problem

Kinetic energy is the energy of an object due to its motion. Just like potential energy, kinetic energy is also measured in Joules (J). The basic equation for the kinetic energy on an object is: Ek = ½mv2
Ek is the kinetic energy in an object, m is the mass of the object measured in kg, and v is the velocity of the object.

Example Problem

Power is the rate at which work is done by, in which the energy is transferred. Power is measured in watts (W), and one watt= one joule of energy transfered in one second.

Power Example Problem

Efficiency is the ratio of the work done on the machine to the work put into the machine.

Work is the product of the force and displacement of an object in the direction of the force. Work is measured in Joules (J). To determine the amount of work being done you use the formula:

Work Example Problem

Temperature: Temperature is the measure of the average kinetic energy of particles in a substance. In a hotter object, the particles are moving faster and have a larger average kinetic energy. And in a colder object, the particles are moving slower and have a smaller average kinetic energy. Temperature does not depend on the number of particles, if a 2 kilogram mass of iron is at the same temperature as a 3 kilogram mass of iron, the average kinetic energy of the particles in both masses is the same.

Thermal Energy: Thermal energy is the measure of the total amount kinetic energy of particles.

Specific Heat Capacity: The specific heat capacity of a solid or a liquid is heat that is used to raise unit mass of a substance by one degree. In SI units, specific heat, is measured in J/kg x K. Specific heat can also be used to find out the amount of heat that must be transferred to change the temperature of a given mass by any amount needed.

Q = mc∆T

Q= Heat supplied to substance,
m= Mass of the substance,
c= Specific heat capacity,
T= Temperature rise (change in temperature)

Specific Heat Example Problems

Relate energy transformation to work done:
Example: A Rollercoaster
A rollercoaster often begins when a chain and motor exerts a force on the train of cars to lift the train of cars up to the top of a very steep hill, once the cars are lifted to the top, gravity will take over and the rest of the ride is experienced in energy transformations. As well, a rollercoaster shows the work and energy relationship. The work done by the external forces is capable of changing the total amount of mechanical energy from an initial value to the final value. The amount of work that is done by the external forces on the object is equivalent to the amount of change in the total mechanical energy of the object. When energy is transferred, work must be done on the object.

Law of Conservation of Energy:
Energy in a system can have many forms such as, kinetic, potential, heat, light, etc. The law states that energy can neither be created nor destroyed, but can be transferred or transformed from one form to another. The total amount of energy in a closed system never changes.

Potential Energy Equation: Ep = mgh

Kinetic Energy Equation: Ek = ½mv2

Energy Example Problems