UNIT 4: ENERGY
ENERGY
1. Energy
Energy
- Energy is the ability to do work.
- Work is done when a force acts on a body and there is displacement in the
direction of the force.
- The unit for energy is joules.
Types of energy
- Two main types of energy are kinetic and potential.
- Kinetic energy: energy which a body possesses by virtue of being motion.
Electric energy → kinetic energy
Thermal (heat) radiant energy → kinetic energy
Light energy (radiant) → kinetic energy
- Potential energy: “stored energy”
Elastic energy → potential energy
Chemical energy → potential energy
Nuclear energy → potential energy
Transfer of energy
- Work done is the energy transferred.
- Energy is able to be transferred from one form into another.
Ex: chemical energy in battery changes to electrical energy which is converted to
light and heat in the bulb.
Potential energy
- Potential energy is stored energy.
- PE = mgh
- M is mass, g is gravity (9.8) and h is height.
- Unit for energy is Joules (J).
- If a 2kg ball is resting on a table 2 meters above the ground, the GPE is
2x2x9.8=39.2J
GPE = MGH
- If a .45kg apple is hanging from a tree 4.2 meters above the ground, what is the
GPE?
, UNIT 4: ENERGY
Kinetic energy
- Kinetic energy is energy in motion.
- The kinetic energy of a moving object can be calculated by using the formula.
- KE = ½ mv ^2
- M is mass, v is the velocity
- V has a bigger impact on KE than mass
- Unit is Joules (J)
- The KE of a 2-kilogram ball rolling at 2 m/s is 4J.
KE = ½ mv ^2
- What is the KE of a .25 kg toy car rolling at 1.2 m/s?
- What is the velocity of a .25 kg toy car that has KE of 0.18 joules?
GPE and KE calculations
- GPE = KE
- An object that is resting above the ground has a GPE which can be converted to
KE if the object begins to move.
- Energy is ALWAYS lost to the surroundings, usually in the form of friction and
heat, but we calculate assuming that no energy is lost.
Example:
A skier with a 50 kg mass is at the top of a run with a vertical height of 20cm. What is
the velocity at the bottom of the run (assuming no energy is lost?)
- GPE = KE
- (50)(9.8)(20) = ½ (50) v ^2
- Cancel out the 50
- 196 = ½ v^2
- 98 = v^2
- 9.9 m/s
E = MC^2
- Einstein’s famous equation, which states that energy is equal to mass times the
speed of light * squared.
- Incredible amounts of energy are contained within small masses.
- Signifies that mass-energy is interchangeable.
* = 299792458 m/s !!!!!!!!!
ENERGY
1. Energy
Energy
- Energy is the ability to do work.
- Work is done when a force acts on a body and there is displacement in the
direction of the force.
- The unit for energy is joules.
Types of energy
- Two main types of energy are kinetic and potential.
- Kinetic energy: energy which a body possesses by virtue of being motion.
Electric energy → kinetic energy
Thermal (heat) radiant energy → kinetic energy
Light energy (radiant) → kinetic energy
- Potential energy: “stored energy”
Elastic energy → potential energy
Chemical energy → potential energy
Nuclear energy → potential energy
Transfer of energy
- Work done is the energy transferred.
- Energy is able to be transferred from one form into another.
Ex: chemical energy in battery changes to electrical energy which is converted to
light and heat in the bulb.
Potential energy
- Potential energy is stored energy.
- PE = mgh
- M is mass, g is gravity (9.8) and h is height.
- Unit for energy is Joules (J).
- If a 2kg ball is resting on a table 2 meters above the ground, the GPE is
2x2x9.8=39.2J
GPE = MGH
- If a .45kg apple is hanging from a tree 4.2 meters above the ground, what is the
GPE?
, UNIT 4: ENERGY
Kinetic energy
- Kinetic energy is energy in motion.
- The kinetic energy of a moving object can be calculated by using the formula.
- KE = ½ mv ^2
- M is mass, v is the velocity
- V has a bigger impact on KE than mass
- Unit is Joules (J)
- The KE of a 2-kilogram ball rolling at 2 m/s is 4J.
KE = ½ mv ^2
- What is the KE of a .25 kg toy car rolling at 1.2 m/s?
- What is the velocity of a .25 kg toy car that has KE of 0.18 joules?
GPE and KE calculations
- GPE = KE
- An object that is resting above the ground has a GPE which can be converted to
KE if the object begins to move.
- Energy is ALWAYS lost to the surroundings, usually in the form of friction and
heat, but we calculate assuming that no energy is lost.
Example:
A skier with a 50 kg mass is at the top of a run with a vertical height of 20cm. What is
the velocity at the bottom of the run (assuming no energy is lost?)
- GPE = KE
- (50)(9.8)(20) = ½ (50) v ^2
- Cancel out the 50
- 196 = ½ v^2
- 98 = v^2
- 9.9 m/s
E = MC^2
- Einstein’s famous equation, which states that energy is equal to mass times the
speed of light * squared.
- Incredible amounts of energy are contained within small masses.
- Signifies that mass-energy is interchangeable.
* = 299792458 m/s !!!!!!!!!
