# Forces

• Created by: Amybr13
• Created on: 22-04-17 13:42

## Energy - Two Types

Can be stored for later release (POTENTIAL)

• Chemical Potential energy
• Gravitational Potential energy (GPE)
• Elastic Potential energy
• Nuclear energy

'Energy on the move' can NOT be stored

• Kinetic energy
• Light energy (or radient)
• Heat energy (thermal)
• Electrical energy
• Magnetic energy

You will always have an input energy and output energy, e.g a candle has chemical energy as an input energy, which then turns into Light energy and heat energy. What the purpose of your candle is, the other is the waste energy.

1 of 6

## Conservation and Dissipation of energy

• Energy can be storred in a variety of different energy stores
• Energy is transferred by heating, by waves, by an electircal current or by a force when it moves an object
• When an object falls and gains speed, its store of GPE decreases and its kinetic energy store increases
• When a falling object hits the ground without bouncing back, its kinetic energy decreases. Some or all of its energy is transferred to the surroundings. The termal energy store of the surroundings increases and energy is transferred by sound waves
2 of 6

## Wasted energy

A law of Physics states that 'no machine is 100% efficient'. In fact, it is impossible to have such a machine. There will always be wasted energy output.

We use SANKEY DIAGRAMS  to show how much energy output is useful and wasted for any device.

Efficiency = Useful energy output

Total enegy input

It has no units but can be written as either a decimal or number or as a percentage.

3 of 6

## 'WORK'

Work in physics implies 'moving' something. (example: Pushing a wall means no work done unless you move a wall.)

Work = Force X distance

Joules, J = newtons,N X metre ,m

Positive work is when the object gains speed. On the other hand, Negative work is when the object loses energy, e.g Friction.

TO GAIN HEIGHT = GPE                                                                                                                                                   GPE = Weight  X  Height                                                                                                                   GPE = m X g X h

TO GAIN SPEED = KE                                                                                                                                                      KE = 1/2 X mass X velocity2                                                                                                              KE = 1/2 X m X v2

4 of 6

## Elastic Potential Energy

TWO KEY IDEAS:

1. The extetion of a spring is directly proportional (HOOKES LAW) to to applied force (if the spring is not overstretched)

F = K.e

2. The area under the graph is the energy stored by the spring (its elastic potential energy)

Area = 1/2 X b X h                                                                                                                                      = 1/2 X e X f                                                                                                                                          OR                                                                                                                                                = 1/2 X e X (Ke)

= 1/2 X K X e2

5 of 6

## Big energy issues

• Gas fired power stations and pumped-storage stations can meet variations in demands
• Nuclear, Coal and Oil power stations can meet base- load demand
• Nuclear power stations, fossil-feul power stations using carbon capture and renewable energy are all likely to contribute to future energy suppilies.

Supply and demand

The demand for electricity varies during each day. Its also higher in winter than in summer. Our electircity generators need to match these changes in demand.

Renewable energy - The amount of electricity they generate depends on conditions, e.g wind

Non- renewable energy comes from sources that will run out or will not be replenished in our lifetimes.

Nuclear energy - Produces radioactivity which is dangerous to humans and the environment. it also needs high maintenance.

6 of 6