1. Energy

2. 
What is Energy?
Energy (symbol E) is the ability to do work or make something happen
Energy is measured in units called Joules (symbol J)

3.  Types of Energy There are two types of energy;
Kinetic Energy (symbol EK) - active energy, energy that is doing something
Potential energy (symbol EP) - stored energy, energy that has the potential to do work

4. 
Kinetic Energy (EK)
Active energy, whenever you can see, hear, feel something happening kinetic energy is being used.
Examples of EK include;
Heat energy
Sound energy
Light energy
Movement energy (Kinetic energy)
Electrical energy

5.  Potential Energy There are three forms of EP
Gravitational potential energy
–energy stored because an object is at a height
Elastic potential energy
–energy stored in stretched or compressed springs or rubber
Chemical potential energy
–energy stored in the chemical bonds of chemicals

6. The Law of the Conservation of Energy
The Law of the Conservation of Energy
Energy cannot be created or destroyed only transferred (from one object to another) or transformed (from one type to another)
The total amount of energy in the universe remains the same it just moves from one object to another or gets transformed from one type to another

7.  Formulae Kinetic Energy Gravitational Potential Energy
All about movement so it’s formula involves velocity
Gravitational Potential Energy
About the effect of gravity so height is important
Where; EK= Kinetic energy (J)
m= mass (kg)
v=velocity (ms-1)
Where; EP= Potential energy (J)
m= mass (kg)
g=acceleration of gravity (ms-2)

8. 
Exercises
A 58kg skateboarder travels at 4.5ms-1. Calculate his kinetic energy J
A 0.65kg netball travels at 12ms-1. Calculate the ball’s EK J
A 15kg toddler stands at the top of a 2.5m slide. What is her potential energy (g=10ms-2) J
A cyclist and cycle (total mass 92kg) stand at the top of an 85m rise. Calculate their EP (g=10ms-2) J

9. 
Tricky Ones
An ice skater has 557J of kinetic energy and is moving at 4.5ms-1. Calculate her mass kg
A cricket ball (0.16kg) has 96J of EK. Calculate the velocity of the ball ms-1
A flower pot (0.8kg) on a shelf has 12J of potential energy. Calculate the height of the shelf.
1.5m
A cart sitting at the top of a 25m rise has 12000J of EP. Calculate it’s mass kg

10. The Concepts
What happens to the potential energy of the cyclist as she rides down the hill?
All Potential Energy
12000J
1/2 Potential Energy
6000J
All Kinetic Energy
12000J
1/2 Kinetic Energy
6000J

11. Work and Power Work and energy are the same concepts
(so both measured in Joules (J))
When a force acts on an object work is done
The rate at which energy is used or work is done is called Power (measured in Watts (W))
Where; W= work (J)
F= force (N)
d= distance (m)
Where; P=power (W)
W= work (J)
E=energy (J)
t= time (s)

12. Exercises
A student pushes a door closed with a force of 2N for a distance of 0.75m. Calculate the work done J
A mother pushes a child on a swing with a force of 12N for a distance of 0.45m. Calculate the work she does J
The student in 1. pushes the door for 0.4s. What is the power she applies to the door? W
The mother in 2. pushes the child for 1.1 s. What is her power output? W