# WEP Definitions

Work Energy and Power

Energy is the ability to do Work.

Work is the transfer of Energy.

The verb, to do, is also a good idea into energy. When something is done, a form of energy was transferred from one thing to another thing. If you are doing something you are converting energy, if you have to do something you might think of the effort, the effort of doing that energy.

We define work as being when a force moves a body some distance, this work is equal to the amount of energy added to the system.

Definition and units for work and power We define work as being when a force moves a body some distance, this work is equal to the amount of energy added to the system.

Work is measured in Joules (J) These are the same units that measure energy.

1 J = 1N x 1m

Write the equation for Work and the equation triangle in your notebooks:

Give Example

A trolley is pushed by a boy 400m with a constant force of 30N, calculate how much work was done?

How much work is done when a catapult recoils 22cm projecting a stone with a force of 456N ?

A push go-cart of mass 20kg is pushed by a boy a distance of 400m calculate the

Work Problems

Lets try some problems now

Question 1

Calculate the work done when a force of 10 newtons acts through a distance of 50 metres in the direction of the force.

Question 2

A girl pulls a sled a distance of 100 m. If the force exerted by the girl is 80 N, calculate the work done.

Question 3

A car of mass 500 kg accelerates at 3 ms-2 from rest. How much work is done after it has travelled 100 metres?

If someone was to sit on you, you would feel the force of them. This force is called their weight. At the beginning of this course you may have been told or saw that when you 'weigh' something on a balance this is called mass. Mass and weight are very closely linked, but in science we need both words to mean different things.

but to find weight

In science, weight is measured in newtons. On Earth g= 10m/s2

On Earth a mass of 1 kilogram has a weight of 10 newtons,

If you want to find the weight of a body, multiply its mass by 10.

Now you should go and do the questions in the book.

## Energy

Energy is the ability to do work.

So if you do work you use energy!

What do you think the units of energy are?

WOW thats right! the same as the Units for Work, the Joule!

There are no pictures of energy !

Any object may possess energy, but the object

It is important to realize that in physics today, we have no knowledge what energy is.

Richard Feynman

Energy can't be created or destroyed but it can change from one form to another

This is called the Principle of Conservation of Energy, this means to us that if we want to use energy we have to get it from somewhere else. Also if something is using energy then that energy doesn't just disappear it turns into other forms of energy.

What forms of energy are there ?

Give 6 different examples of energy being used, we will use your list to name the different types of Energy.

1. ________________________
2. ________________________
3. ________________________
4. ________________________
5. ________________________
6. ________________________

A list of the various types forms of energy.

Kinetic,

This the form of energy that moving bodies have. If something is moving it is said that is has kinetic energy, because it would take work to stop the body moving. Heat,

All bodies have heat energy, even what we call thing that we think are cold, are not as cold as they might be. They have less heat energy but they still have some. Heat energy is the energy of all the particles (molecules or atoms) added together. Sound,

When you hear noise that is sound energy. Sound is caused by vibrations, vibrations are movements and so sound energy is very similiar to kinetic energy, because the body is moving.

Light,

Light Energy is given off by Hot objects, light comes in little waves.

We see because light enters our eyes. Our brains and eyes together build up a map of things around us. If there is no light energy we cannot see, as none can enter our eyes. The Light we see is only a little part of the radiation spectrum given off from objects. ### Rattlesnakes and other pit vipers use their eyes to see during the day. But at night they use infrared sensory organs to detect and hunt warm-blooded prey. These infrared "eyes" are cuplike structures that form crude images as infrared radiation hits a heat sensitive retina.

Electrical,

Electrical energy is created between bodies that have different charges between each other, a balloon can cling on to a jumper and defy gravity and the force of its weight, due to electrical charge. Our whole lives are helped by the presence of electrical energy in our homes, workplaces, schools, hospitals, in fact it is very hard to imagine life without electricity! Potential Energy

Is Stored energy

Mechanical potential energy

This is the energy that a body has because of its position. Imagine a rock on the ground, can it move? Imagine a rock teetering on the edge of a cliff, can it move? A stone in a catapult, it has no kinetic energy because it is not moving but the elastic properties of the sling will propel it if it is released. This is what is meant by potential energy.

Chemical

Chemical energy is the energy within molecules that when reacted with some other material gives out energy. When our cells collect energy from the blood it then reacts with oxygen. When we burn materials in oxygen we also react the materials, we are all aware of the heat and light energy that comes from the fire. Other examples include chemical reactions, the reactions inside batteries. Nuclear,

Nuclear energy is the huge supply of energy that is found in the Nucleus of the Atom, If we break the bonds inside the Nucleus we can release great energy. Usually Nuclear energy is used to make electricity in many countries, the UK, France, Germany. However it has not yet been used in Ireland previously due to safety concerns. Elastic

The energy stored in a spring or elastic is really potential energy. That is energy due to position away from the equilibrium point.

http://en.wikipedia.org/wiki/File:Watch_movement.png

catapult the trebuchet taken from http://www.people.carleton.edu/~coughlim/animations.html

Power

Power is the amount of work that can be done in a certain unit of time

Power is the rate at which work is done Power = Work / Time

(Watt) (J) (s)

page 321 q1-6