Energy Unit overview
The capacity of a system (physical object) to do work. It’s forms are heat, kinetic or mechanical, potential, sound as well as others like nuclear, electrical, and magnetic.

Potential energy is that energy which an object has because of its position. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy. If you lift a mass upwards, its potential energy will be increased. This is Gravitational Potential Energy. [Potential Energy: Joule = mass x gravity x Height {mgh}]
1.) If a ball that has a mass of 1.96N is held over a 24 meter high building, what is its potential energy?
2.) If the same ball is dropped, at what height is the potential energy 7.84J:
  1. a. On earth?
  2. b. Where gravity is 20m/s²?
  3. c. Gravity is 4m/s²?
3.) 2 men are hoisting a grand piano up 8 meters to an apartment using a winch system. When it reaches the top, it has a potential energy of 28,459.2J to fall on a silent film actor. If it does fall, how much mass of piano will hit the actor?
Power is the time rate at which work is done or energy is transferred. In calculus terms, power is the derivative of work with respect to time.

Power is measured in Watts (W) or Joules per second (J/s)
Reminder: Work = Force x displacement


1.) If a generator puts out 2,500,000J in 30 seconds (awesome generator, I know), what’s its power?
2.) Bill moved a 50kg box up onto a ledge 2 meters high in 47 seconds, but Will moved a 36kg box to the same height in 28 seconds. Who did more work?
3.) An escalator is used to move 20 passengers every minute from the first floor of a department store to the second. The second floor is located 5.20 meters above the first floor. The average passenger's mass is 54.9 kg. Determine the power requirement of the escalator in order to move this number of passengers in this amount of time.

Efficiency is a very easy concept. You just need to be able to calculate percentages. If I asked you to calculate the efficiency of a transformer, what you got to do is think about how much energy the transformer takes from the mains, and how much of this energy is used in a useful way. Basically, what percentage of the energy is used usefully? It would be nice to say 100% but it is probably only 80% efficient.
Well, nothing is perfectly efficient. If you have a cellphone, which you do, you will have noticed that the charger gets kind of warm when you use it to recharge the battery of your cell. This means that some of the electrical energy has been wasted, ie turned into heat.

The way to calculate the efficiency of something is:
(Output/input) x 100
So, for every 200J of energy supplied to a hairdryer, 80J is useful while the other 120J is wasted. So:
80/120 = 0.4 x 100 = 40% efficiency

Combustion engine 10-50%
Gas turbine up to 40%
Gas turbine plus steam turbine (combined cycle) up to 60%
Water turbine up to 90% (practically achieved)
Wind turbine up to 59% (theoretical limit)
Solar cell 6%-40% (technology dependent, 15% most often, 85%-90% theoretical limit)
Firearm ~30% (.300 Hawk ammunition)
Fuel cell up to 85%
Electrolysis of water 50%-70% (80%-94% theoretical maximum)
Photosynthesis up to 6%
Muscle 14% - 27%

Thermal energy: is the total amount of kinetic energy within a system. If you increase the energy a system contains, you increase the speed of the particles which in turn increase the overall thermal energy of a system.

Energy is transferred in the form of heat; heat does not refer to the temperature of the object but is closely related. Heat is the warmth that is felt when you put your hand over a hot stove; temperature is the potential for heat transfer. Thermal energy can be transferred in three forms conduction, convection and radiation. Heat is also defined as the energy of the substance and temperature measures the energy within a substance, the energy is measured in Kelvin. A change in temperature results in a change of energy within a system, so if energy is raised in a system the temperature is raised, if energy is taken away then the systems temperature is decreased.

Conduction: Conduction is the transfer of energy from a hot system to a colder system; particles vibrate or collide into each other transferring energy to another particle, two or more systems continue to transfer energy until thermal equilibrium is achieved. Conduction can occur in all forms of matter.
Convection: is the movement of particles within fluids or gases, convection cannot occur in solids because particles cannot flow or have a significant diffusion occur within the system. Convection occurs through the method of diffusion, particles within a heated region move out into a colder region and particles within a cold region move into a warmer region.

Thermal Radiation: is the electromagnetic radiation created by motion of the particles within a system, all systems with a temperature greater than absolute zero can give off thermal radiation. Some examples of thermal radiation could be: the light from a light bulb, infrared radiation given off by living creatures and the light from the sun.
Specific Heat Capacity: is the required amount of heat required to change the substances temperature by one degree. Different systems require a different amount of heat to changes its temperature by one degree, therefore different systems have different freezing and boiling points.
Q = mcΔt
Q= thermal energy (joules)
m = mass (kilograms)
Δt = change in temperature (°C)
C= specific heat capacity

Law of Conservation of Energy: is the rule that states that energy cannot be created or destroyed; energy can only be changed into different forms. For example an object is lite on fire, the object burns creating heat energy, light energy and sound energy, the forms of the energy is changed but not destroyed therefore conserving the energy of the object.

Having these equations allows us to solve problems using the law of conservation of energy, the law states that energy is not created nor destroyed therefor must always be present, so the intial energy must equal the final energy which gives us this equation.

Kinetic energy: is the energy of motion, if an object is still, it has potential energy, but once that object starts moving that energy is changed into kinetic energy. There are multiple forms of kinetic energy, vibrational, rotational and translational.

this equation allows us to determine the kinetic energy of an object, using the mass multiplied by the velocity squared divided by one half.
M= mass (kg)

V= velocity

KE = Kinetic Energy ( J)
Example: A car is moving down a highway at 55m/s, the car weighs about 1500kg determine the kinetic energy
Ke = ½ * m * v2 = ½ * 1500 * 55 = 41250 joules of kinetic energy (KE)

Relate Energy Transformation to Work Done:
E= energy
W= Work
Δ = Delta
knowing ΔE is equal to the work done we can state that energy transformation is equal to the work done on an object.