Physics: Chapter 6 - Energy, Work and Power

6.1 Energy
Energy is the capacity to do work.
SI Unit: joule (J)

Types of energy:

1. Kinetic Energy
   
2. Potential Energy (Chemical potential, elastic potential and gravitational potential)

1. Kinetic Energy
Moving objects have kinetic energy.

2a. Potential Energy - Chemical Potential Energy
Can be found in food, fossil fuels.

2b. Potential Energy - Elastic Potential Energy
A spring or rubber band possesses elastic potential energy when compressed or stretched.
When released, it is converted into kinetic energy.

2c. Potential Energy - Gravitational Potential Energy
The higher the object that leaves the ground, the greater the gravitational potential energy.

Principle of Conservation of Energy

Energy can neither be created nor destroyed in any process. It can be converted from one form to another or transferred from one body to another, but the total amount remains constant.

Conversion of energy
Efficiency = useful energy output divide energy input times 100%

6.2 Work

Work done by a constant force on an object is given by the product of the force and the distance moved by the object in the direction of the force.

W=F(s)
Work done by a constant force = constant force(distance moved by the object in the direction of the force)

One joule is defined as the work done by a force of one newton which moves an object through a distance of one metre in the direction of the force.

No work is done when:

1. The direction of the applied force and the direction in which the object moves are perpendicular to each other, and
2. The force is applied on the object but the object does not move.

Mechanical Energy

1. Kinetic energy and work done
2. Gravitational potential energy and work done

1. Kinetic energy and work done
Kinetic energy = 1/2(mass of body)(speed of body)²

2. Gravitational potential energy and work done
Ep = mgh
Potential energy = mass(gravitational field strength)(height)

6.3 Power
P= W/t = E/t
Power = work done over time = energy converted over time
SI Unit: watt (W)

One watt is defined as the rate of working or energy conversion of one joule per second