Will, Joel, Ryan


Efficiency: the dictionary definition of efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms

An example of an object with a poor efficiency rating is an old light bulb it is most likely not going to very efficient. This is because it does not do entirely what it is designed to do. It is designed to put out light and not heat. But these old version light bulbs put out a lot of heat. Therefore they are not energy efficient because all the electrical energy that it is receiving is not entirely being transferred into light energy, some of the energy the bulb is receiving is being turned into thermal energy. In this case the efficiency of an incandescent light bulb is only 5-10%. The new florescent light bulbs are much more efficient than the older incandescent bulbs because they are designed to put out less heat and more light. These new bulbs are running an efficiency rating closer to 80%

An object with a high efficiency rating is an electric heater. This is because all the electrical energy the heater is receiving is being turned into the type of energy it is designed to create, thermal energy. The efficiency rating of an electrical heater is 95-100%
A list of common everyday items are here at http://en.wikipedia.org/wiki/Energy_conversion_efficiency
Example of energy conversion efficiency

Energy efficiency
Combustion engine
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)
~30% (.300 Hawk ammunition)
Fuel cell
up to 85%
Electrolysis of water
50%-70% (80%-94% theoretical maximum)
up to 6% [2]
14% - 27%
Electric motors
30-60% (small ones < 10W); 50-90 (middle ones between 10-200W); 70-99.99% above 200W
Household refrigerators
low end systems ~ 20%; high end systems ~ 40-50%
Incandescent light bulb
Light-emitting diode
up to 35% [3]
Fluorescent lamps
28% [4]
Low-pressure sodium lamps
40.5% [4]
Metal halide lamps
24% [4]
Switched-mode power supply
currently up to 95% practically
Electric shower
90-95% ( Overall it would be more efficient to use a heat pump, requiring less electric energy)
Electric heaters
around 95% (all energy is always converted into heat anyway)

Efficiency uses a simple formula it is:

Work: work is the amount of energy transferred by a force acting through a distance in the direction of the force. Like energy, it is a scalar quantity

There are two different formulas that can determine the amount of work done on a object they are.
W=Fd this equation states that the work done on the object is equal to the Force normal of the object multiplied by the displacement of the object.

If the force applied to an object is parallel and in the same direction the object the work done is positive. If the force is parallel to the direction but is in the opposite of the direction the object is travelling the work done is negative.

When the force applied to an object is not parallel to the direction the object is travelling and is on an angle only the component of the force in the same direction as the displacement does work. Therefore if the force applied is perpendicular to the object no work is done.

The second formula to find the work done on an object is W=ΔE
So this formula states that the work done on an object is equal to the change in energy of the object. This is normally the change of kinetic energy into potential energy. So the mechanical energy always stays the same just the kinetic energy is transferred into potential energy when the object changes its height compared to its reference point.

An example of an object having work done on it through the change of its height is lets say an object of 2kg has a speed at 2 meters above its reference point is 12m/s when the object is 12 meters above its reference point it will have an increase in its potential energy, but its mechanical energy will be the same. This is because the object is velocity is now slower making it kinetic energy smaller. The reason that work is done in this situation is because the values of both the potential and kinetic have changes therefore work has been done on the object.
Let’s solve the problem stated above. An objects speed at 2 meters above its reference point is 12m/s when the object is 12 meters above its reference point how much work has been done on the object? Its mass is 2kg.
If you worked it out you find that there is an increase of 196J of potential energy therefore the work done on the object was 196J.
Now let’s solve a work problem using the force applied to the object and its overall displacement. An object is 6 meters away from the edge of a table and a person moves the object to the edge. The table is frictionless. The person exerts 80N of force on the object. How much work did they do to move the object?

If you worked it out the answer should have been the person put out 480J
of work to move the object.

Other good work and energy question can be found at: http://www.sparknotes.com/physics/workenergypower/conservationofenergy/problems_1.html#explanation5


Kinetic Energy: is the energy an object possesses when it is in motion. It is just one type of energy, there are several other types of energy including potential, thermal and light.
The equation for calculating kinetic energy is:
external image u5l1c1.gif
KE: is kinetic energy (sometimes shown as Ek) is is measured in joules (J)
m= mass (kg)
v= velocity

This is a helpful resource when trying to understand kinetic energy, the simulation shows the potential vs kinetic energy or skateboarder: Skate Park Sim
(select "Show Pie Chart" to see the kinetic energy of the skateboarder)

A leopard is chasing an impala at a velocity of 20m/s, this adult leopard has a mass of 117 kg. What is the kinetic energy of this leopard?

We will now use our formula to determine the Ek of the leopard.
mass of leopard: 117 kg
velocity of leopard: 20 m/s

Ek = 1/2(117kg)(20m/s2)
Ek of leopard = 23400 J

That same impala has a mass of 40kg and and Ek of 9680 J. Will the leopard catch the impala? (it the leopard faster)

We will now use the same formula to find the velocity of the impala:
Ek of impala: 9680 J
mass of impala: 40 kg

9680= 1/2 (40)(x2)

Use algebra to isolate velocity:

9680/(1/2)(40) = x2
9680/20 = x2
484 = x2
√484 = x

x = 22

The impala's velocity is 22 m/s, the leopard is slower and won't catch the impala at those speeds.


Definition: the sum of the kinetic energy and potential energy of an object. It does not include thermal energy, sound energy, chemical potential energy, etc.

  • "the total energy of a closed system is conserved" (total amount of energy does not change)
  • energy may be transferred from one form to another"
  • when friction is present it will cause some mechanical energy to change into other forms of energy (ie. sound, heat, or light)

The simplest equation for the law of conservation of energy is:

Ei = Ef

It can be further expanded to:

Eki + Epi = Ekf + Epf (keep in mind this is without friction)

Even further to:

(1/2)(mi)(vi2) + (mi)(gi)(h) = (1/2)(mf)(vf2) + (mf)(gf)(hf)

When friction is encountered we can modify the equation to include:
But before this, the equation for Wf (work of friction, Wf = [J]) is: Wfr = (Ffr)(d)

So the equation will be:

(1/2)(mi)(vi2) + (mi)(gi)(h) = (1/2)(mf)(vf2) + (mf)(gf)(hf) + (Ffr)(d) ------> because the friction removes kinetic energy, the Wfr equation is added to the final side.

With Friction:

What is the final speed of a ski jumper leaving the jump who is competing in the Winter Olympics? His mass is 80 kg, his initial speed was 0m/s, the top of the jump is 200 m in height, and the elevation of the end of the jump is 20 m. What was his final velocity? Friction is negligible.
So, we can plug all that into our equation:

(1/2)(80 kg)(0 m/s2) + (80 kg)(9.8)(200) = (1/2)(80 kg)(v 2) + (80kg)(9.8)(150m)

Use algebra to solve:
(0) + (156,800) = (40)(v2) + (15,680)
156,800 = 40v2 + 15,680
40v2 = 156,800 - 117,600
v2= 39,200
v = √39,200
v = 197 m/s

As is obvious, a skier could never travel that fast, this is just an example to demonstrate the formula.

Power is the rate at which work is being performed. Work does not measure the time it takes for an event to be performed. If one person is walking on a steep inclined hill, and another person is walking on a low inclined hill, the person on the high inclined hill will take longer to get to the same place as the low inclined person. They did the same work, but in different time. This is power.

A box that weighs 575 N is lifted a distance of 20m stright up by a rope. The job is done in 10s. What power is developed?

W= FxD

W= 575 x 20
= 11500j

= 11500j / 10
P= 1150W

Energy is the ability to do work, but more importantly, it means the ability to make something happen. When you exert a force on an object, something has to happen. Energy can be transformed into different types of energy such as Kinetic, Potential, and Thermal energy. When comparing these things to the definition of energy, we can say that potential energy has the “potential” to make things happen. When energy is used it will change the condition of something, whether it be moving an object or changing its temperature or shape.

Gravitational potential energy is the energy gained from an objects position from the earth. When an object is lifted into the air, it gains more gravitational potential energy because it has more potential to gain energy due to gravity (9.8m/s2 down).

PE gravitational = mgh

Thermal energy is transferred from a hot body to a cold body. When thermal equilibrium is reached, the transfer of energy between bodies is equal. Thermal energy starts with the Kinetic Molecular Theory, which states the assumption that matter is mad up of many tiny particles that are always in motion. In a hot body, the particles move faster, and thus have a higher energy than particles in a cooler body.
When an object is "hot" or has a lot of thermal energy, the atoms and molecules within the object are "vibrating" more than in a cooler object. The particles in a hot body have larger kinetic and potential energies than the particles in a cold body.

The specific heat capacity of a solid or liquid is defined as the heat required to raise unit mass of substance by one degree of temperature.
The units are joules per Kelvin. They are represented by C.
The higher the C value, the more difficult it is to “warm” the substance up.
In order to find the specific heat capacity using the equation below you need to know the following:
energy transferred into heat [joules] (Q)
mass of substance [g] (m)
change in temperature of the mass [C] (Tf- Ti) (delta T)

Temperature is a measure of the average kinetic energy of the particles in a substance. The temperature of a substance is a result of the speed at which its molecules are moving. Temperature determines the direction of internal energy flow between two systems when heat is being transferred. In a hotter object, the particles are moving faster, and have a larger kinetic energy. And in a colder object, the particles are moving slower, and have a smaller kinetic energy. Temperature can be measured in Celsius or Kelvin. Temperature scales were developed by scientists to allow them to compare their temperature measurements with those of other scientists.

The formula to find temperature in Kelvin is, K = C (Celsius)+ 273
The formula to find temperature in Celsius is, C = K (Kelvin) – 273
Zero degrees Kelvin is equivalent to -273 degrees Celsius, and -459 degrees Fahrenheit


A 2 x 10^2g sample of water at 80 Celsius is mixed with 2 x 10^2 g of water at 10 Celsius. Assume no heat loss to the surroundings. What is the final temperature of the mixture?

A 1 x 10^2g aluminum block at 100 Celsius is placed in 1 x 10^2g of water at 10 Celsius. The final temperature of the mixture is 25 Celsius. What is the specific heat of the aluminum?