Energy

SC Physical Science StandardsPS-6.1

Explain how the law of conservation of energy applies to the transformation of various forms of energy (including mechanical energy, electrical energy, chemical energy, light energy, sound energy, and thermal energy).

PS-6.2 Explain the factors that determine potential and kinetic energy and the transformation of one to the other.

Energy: The ability to do work.

James Prescott Joule Studied transformations of energy, devised many of the energy calculations we use today. Joule (J)- SI unit of energy.

Law of Conservation of Energy•Energy may change from one form to another, but the total amount of energy never changes.

Forms of Energy1. Mechanical

Energy due to something’s position or motion. It is either potential, kinetic, or the sum of the two.

2. ChemicalEnergy associated with chemical bonds between atoms or ions. Transformations occur during chemical reactions.

3. NuclearEnergy associated with reactions involving the nucleus of

the atom.4. Electrical

Energy associated with current and voltage.5. Thermal (Heat)

Energy associated with movement of particles.6. Light

Energy associated with electromagnetic waves.7. Sound

Energy associated with longitudinal waves.

Mechanical: • Potential Energy-

– Energy is greater when height above ground is greater, due to gravity.

– Energy is greater when weight is greater, due to gravity.

• Kinetic Energy-– Energy is greater when speed is

greater, due to motion.– Energy is greater when mass is

greater, due to motion.

Transformation:• The different types of energy can

change from one form to another without changing the total amount of energy…

• Here are some examples:

What energy transformations are taking place?

Electrical to light / thermal Chemical

to heat

Chemical to light / sound

Electrical to radiant

Kinetic to electrical

Nuclear to electrical

Radiant to electrical

Conversions between KE and PE• Mechanical energy – the total

amount of kinetic and potential energy in a system

Falling objects – Gravitational potential energy is converted to kinetic energy

The Law of Conservation of Energy

- energy cannot be created or destroyed; it can only change forms

Following Energy’s Trail• If energy is conserved, why do

objects that are moving eventually stop (seem to lose energy)?– The energy is converted to other

forms

Converting Mass into Energy• Two processes convert a small

amount of mass into a large amount of energy– Nuclear fission – the splitting of an

atomic nuclei

– Nuclear fusion – the combining of small nuclei• This is what powers the sun

Energy and The Human Body• We get our energy from the foods we

eat (chemical potential energy)• We convert that energy to kinetic

energy, sound energy, & thermal energy

• The energy we get from foods is measured in Calories– 1 Calorie = 4,184J

Example #1• An object on the ground has zero potential energy.• Lift it to some height, it now has PE equal to the work it

took to lift it to that height. Its PE depends on its weight and height above the ground.

• Drop the object and the PE is transformed to kinetic energy as it speeds up due to the attraction of gravity. However, the total energy remains the same, throughout the transformation.

• Just before the object hits the ground, most of the PE is now KE. It has lost the PE because its height has returned to nearly zero.

• When it hits the ground, some of the KE will be transformed again to sound energy and thermal energy as the particles speed up when they strike the ground.

Example #2• A swinging pendulum has mechanical energy (both

potential and kinetic energy are involved in the swing).

• At the top of the swing PE is greatest; and depends on its height and weight.

• KE is greatest at the bottom of the swing because the speed is greatest.

• Between top and bottom, PE is transforming to KE because of the changes in both height and motion.

• Eventually the pendulum comes to a stop because of friction.

• Friction transforms mechanical energy to thermal energy.

Example #3• A light bulb is glowing in an electric circuit powered

by a battery.• Chemical energy transforms to electrical energy.• Electrical energy (electrons) flows through the bulb

transforming to light and thermal energy due to the resistance of the filament to the movement of the electrons through the wire.

• The total energy from the chemical reaction of the battery is equal to the total energy that it transforms into in the form of light and heat through the bulb and through the wires.

Example #4• A baseball is thrown from the catcher to the first

baseman.• The catcher transforms chemical energy from food

to mechanical energy when moving her arm to throw the ball.

• The work done on the ball converts the moving (kinetic) energy of her arm to KE of the moving ball.

• When the first baseman catches the ball, the ball does work on his hand and glove, giving them some mechanical energy.

• The ball also moves particles in the glove upon impact, transforming KE to thermal energy when it is caught.

• The player catching the ball absorbs the energy of the ball and this energy is turned to heat.

• The total heat energy produced in the first baseman is equal to the energy used to throw the ball by the catcher.

Other Examples…• A swing- Kinetic energy to Potential

energy and back again to Kinetic• Friction- Mechanical energy to Thermal

energy• Nuclear Fusion and Fission- Mass

becomes energy• Digestion- Chemical bond energy to

thermal energy, mechanical energy, etc. depending on your bodies need