Download Chapter 15: Energy

Chapter 15: Energy
(15.1 Energy and its forms, 15.2 Energy conversion and conservation, 15.3 Energy resources)
15.1: Energy and its Forms
Energy
Energy is the ability to do work. (Energy is transferred by a force moving an object through a
distance.)
Work and energy are closely related. When work is done on an object, energy is transferred to that
object. Work is a transfer of energy.
Both work and energy are usually measured in Joules.
Energy has many different forms (MANY more than this list):
o The sun gives off energy in the forms of heat and light.
o Plants convert sunlight into food than we can eat.
o People convert food energy into muscle movement.
Many forms of energy can be classified into two general types: kinetic energy and potential
energy.
Kinetic Energy
Kinetic energy is the energy of motion.
The kinetic energy of any moving object depends upon its mass and speed.
To calculate the kinetic energy (KE) of an object in Joules, multiply ½ by the object’s mass (m) in
kilograms and the square of its speed (v) in meters per second.
Kinetic Energy (KE) = ½ mv2
(KE = ½ • m • v2)
m = 2 • KE
v2
v = √(2 • KE) / m
Notice that doubling the mass in the first formula would double the kinetic energy, but doubling the
speed would quadruple (“4 times”) the kinetic energy.
Potential Energy
Potential energy is energy that is stored as a result of position or shape.
Examples: holding a ball in the air, compressing a spring, winding a spring.
Potential Energy that depends upon an object’s height is called gravitational potential energy. It
increases when an object is raised to a higher level.
An object’s gravitational potential energy depends of its mass, its height, and the acceleration due to
gravity. The gravitational potential energy an object gains is equal to its mass (m) in kilograms
multiplied by the acceleration of gravity (g) and the object’s height (h) in meters relative to the
ground, floor, or some other reference level.
Gravitational Potential Energy:
Potential Energy (PE) = m•g•h
Doubling either the mass or the height doubles the potential energy.
Elastic Potential Energy is the potential energy of an object that is stretched or compressed.
Stretched rubber bands, compressed springs, wound springs, and super balls are all examples of
elastic potential energy.
Forms of Energy
The major forms of energy are: mechanical, thermal, chemical, electrical, electromagnetic, and
nuclear.
Energy of each type can be converted into other forms of energy.
Mechanical energy is the sum (total) of an object’s potential energy and kinetic energy. (The other
forms of energy do involve potential and kinetic energy, but on an atomic scale.)
Thermal energy is associated with heat. (It is really a measure of how fast an object’s atoms are
moving.)
Chemical energy is the energy stored in the chemical bonds in compounds. When these bonds are
broken, the released energy can do work.
Electrical energy is the energy associated with electric charges. Batteries convert chemical energy
to electrical energy. Lightning is electrical energy.
Electromagnetic energy is a form of energy that travels through space in the form of waves. The
sun gives off electromagnetic energy. Visible light and x-rays are examples. Because they can
travel long distances through air and space, they are often used for communication.
Nuclear energy is energy stored in the nucleus of atoms. Nuclear power plants use fission –
splitting the nuclei of atoms apart to release energy. The sun uses fusion – two hydrogen nuclei
combine the larger helium nuclei. (A tiny amount of mass is lost in the process – which produces
huge amounts of energy.)