Energy
In this article we are going to learn about energy, relating energy transfer to work done and state the unit of energy as the joule. Identify different forms of energy including kinetic and potential. Identify energy conversions and apply the principle of energy conservation to simple examples. Recall and calculate using the expressions: k.e. = ½mv2 p.e. = mgh.
Definition of terms:
Energy: is the ability to do work and exist in different forms. The unit of energy is joule (J).
Relationship between work and energy:
We can relate energy transferred with work done with this equation W = E = F x d.
WHERE: W is the work done, E is the energy transferred, F is the force applied and d is the distance covered or moved.
Forms of energy:
1. Chemical energy: food and fuels, like oil, gas, coal and wood, are concentrated stores of chemical energy.
2. Potential energy (p.e.): this is the energy a body has because of its position or condition.
3. Kinetic energy (k.e.): is any moving body has kinetic energy (k.e.) and the faster it moves, the more k.e. it has. As a hammer drives a nail into a piece of wood, there is a transfer of energy from the k.e.
4. Electrical energy: is produced by energy transfers at power stations and in batteries.
5. Heat energy: is also called thermal or internal energy and is the final fate of other forms of energy. It is transferred by conduction, convection or radiation.
6. Other forms: these include light energy and other forms of electromagnetic radiation, sound and nuclear energy.
Conversion of energy:
Energy: cannot be created or destroyed; it is always conserved.
Calculations of kinetic energy (k.e):
Kinetic energy:
We can calculate kinetic energy with the use of this equation Ek = 1/2mv2
WHERE:
Ek is kinetic energy.
m is the mass of the body.
V is the the velocity or speed of the body.
Worked example:
Question: A car of 4 000 kg mass was moving from Maseru to Teyateyaneng with a speed of 40 m/s. Find the potential energy that was stored in the car.
Solution: First step; We should write our known and unknown variables.
Ek = ?
m = 4 000 kg
V = 40 m/s
Second step; We should write our equation and place variables.
Our formula: Ek = 1/2mv2
Ek = 1/2mv2
Ek = 1/2 x 4 000 kg (40 m/s)2
Ek = 3 200 000 J
The the kinetic energy stored in the car was 3 200 000 J.
Calculations of potential energy (p.e):
We can calculate potential energy with the help of this equation Ep = mgh
WHERE:
Ep is potential energy.
m is the mass of the body.
g is gravitational field strength.
h is the height above the ground.