CHAPTER 15 NOTES
A. Energy – the ability to do work
1. Work is a transfer of energy
2. Kinetic energy – the energy of motion
a. The Kinetic energy of any moving object depends upon its mass and speed
(increasing mass or speed results in greater kinetic energy)
b. KE = 0.5mv2 (one half times mass times velocity squared, labeled in
Joules)
Example: What is Zoey’s kinetic energy if she has a mass of 6 kilograms and a velocity of 2 m/s?
Example: What is the kinetic energy of a 1200 kg car traveling 7 m/s?
Example: What is the kinetic energy of a 1.2 kg textbook sliding across a table at a rate of 2.5 m/s?
3. Potential energy – the energy that is stored as a result of position or shape
a. Gravitational Potential Energy – potential energy that depends upon an
object’s height
b. PE = mgh (mass times acceleration due to gravity (9.8 m/s/s) times
height, labeled in Joules)
Example: What is the potential energy of an object with a mass of 5 kg at a height of 10 meters?
Example: What is the potential energy of a diver with a mass of 50 kg on a diving board at a height of 30
meters?
Example: What is the potential energy of a 1.2 kg textbook at a height of 0.8 meters?
c. Elastic Potential Energy – the potential energy of an object that is
stretched or compressed
B. Forms of Energy – classifications of energy other than kinetic and potential
1. Mechanical energy – the energy associated with the motion and position of
everyday objects. Mechanical energy is not limited to machines – it is the sum of
an object’s potential energy and kinetic energy.
2. Thermal energy – the total potential and kinetic energy of all the microscopic
particles in an object. When an object’s atoms move faster, its thermal energy
increases and the object becomes warmer.
3. Chemical energy – the energy stored in the chemical bonds in compounds.
When these bonds are broken, the released energy can do work. All chemical
compounds, including fuels, store energy.
4. Electrical energy – the energy associated with electric charges
5. Electromagnetic energy – a form of energy that travels through space in the
form of waves. Visible light and X-rays are examples of this energy.
6. Nuclear energy – the energy stored in atomic nuclei. Nuclear power plants use
different methods to process this energy.
C. Energy Conversion and Conservation
1. Energy can be converted from one form to another.
2. Energy conversion – the process of changing energy from one form to another
a. ex: light bulbs convert electrical energy into thermal energy into
electromagnetic energy
b. ex: your muscles use chemical energy moving your hand to strike a match,
friction between the surfaces converts some of the match’s KE into
thermal energy which triggers a chemical reaction releasing stored
chemical energy which starts a fire producing thermal and electromagnetic
energy
3. When energy changes from one form to another, the total energy remains
unchanged.
4. The Law of Conservation of Energy states that energy cannot be created or
destroyed!!!
5. The gravitational potential energy of an object is converted to the kinetic energy
of motion as the object falls.
6. Albert Einstein developed his special theory of relativity in 1905. His theory
included the equation E = mc2 where E is energy, m is mass, and c is the speed of
light. This equation says that energy and mass are equivalent and can be
converted into each other. Energy is released as matter is destroyed and matter
can be created from energy. In nuclear reactions large amounts of energy are
released by the destruction of very small amounts of matter.
D. Renewable Energy Resources
1. Hydroelectric energy – energy obtained from flowing water (like Hoover Dam)
2. Solar energy – sunlight that is converted into usable energy
3. Geothermal energy – the heat beneath Earth’s surface.
4. Biomass energy – the chemical energy stored in living things
5. Hydrogen fuel cell – generates electricity by reacting hydrogen with oxygen