# Energy

### Potential Energy:

When you pick up an item from the floor and place it on a desk, you are applying a force onto that object and displacing it. In other words, you are doing work on it and allowing the object to gain energy. If the object is moved at a constant speed then it is not gaining kinetic energy (energy of movement) but is gaining potential energy (energy of position). This type of potential energy is also called **gravitational potential energy** and is represented by **GPE**. The work done on the object is equal to the change in the gravitational potential energy of the object. The gravitational potential energy of an object can be calculated by using the formula:

**GPE = mass x gravity x height = mgh**

### Kinetic Energy:

Kinetic energy is the energy of motion. When an object falls, it loses height, therefore losing its potential energy. So where did it go? The law of conservation of energy states that energy cannot be created or destroyed, only converted into another form of energy. The answer is that the objects' potential energy gets converted into kinetic energy. The formula for calculating the kinetic energy of a moving object is:

**E _{k} = 1/2 mv**

^{2}

**Kinetic energy of an object = 1/2 x mass x velocity squared**

### Concept Questions:

1. A brick with a mass equal to 2.5kg is lifted to a height of 2.5m above the ground by a bricklayer. Calculate the GPE acquired by the brick.

2. A 75kg skier travels down a 40^{o} slope a distance of 100m. What is his change in potential energy?

3. A brick with a mass of 2kg is thrown at a velocity of 10 m/s. What is its kinetic energy whilst it is in motion?

4. A roller coaster car travels down its track at 20 m/s. Its kinetic energy is 3000 N. What is its mass? (Hint: re-arrange the equation)

### Extra Materials and Videos:

Here are some extra links and youtube videos that may help you further understand the concept of energy. You can watch as many or as little as you like! Just make sure you feel comfortable in working with the physics of energy and that you are able to understand how these concepts fit into roller coaster physics.