E N E R G Y

AIMS

Appreciate how energy affects our lives Describe the environmental considerations

related to energy production Identify renewable energy sources Perform calculations to determine how

much energy is present in a system Produce systems diagrams to show energy

transformations Determine energy efficiency of a system

W H A T I S E N E R G Y ?

Energy is a concept defined as the ability to do work

It is all around us and comes in many different forms

It cannot be destroyed or created but can only be transformed

Machines and living things transform or convert energy

A car converts chemical energy into mechanical energy

A TV converts electrical energy to light energy

Where does energy come from?

Energy in the food we eat comes from the sun

F o s s i l F u e l s

Fossil fuels are combustible and hold much energy

Easily stored and transported

Some challenges in retrieving them

Formed over time from decayed/ compressed matter

Consider

Coal and peat Oil and Natural Gas

Coal and Peat

Dead plants rot slowly in a wet environment

Peat is formed in the early stages of decay

Can be cut and burnt as fuel

Over much longer (100’s millions of years) coal can form due to compression of layers above

Mined in various ways

Oil and Natural Gas

Dead animals compressed over time (as coal) became oil

Some decayed more and became natural gas

Gas is cleaned/ purified and pumped directly to users

Crude Oil has many uses but treated first to produce fuels, chemicals (plastics eventually).

Is a valuable resource

N u c l e a r E n e r g y

Uranium ore mined and used to generate power

Needs to be split to release it’s energy (fission)

Same process as a nuclear bomb but controlled in the reactor

Are serious implications with nuclear power Lethal waste products (lethal for a LONG

time)

Safety

Economic sense (short term solution?)

Environmental Issues

Greenhouse Effect Most of world power derived from Fossil Fuels Burning these fuels releases Carbon Dioxide Is believed that a build up in the upper atmosphere will trap the Sun’s

heat and heat up the planet (Greenhouse Effect)

Acid Rain Burning Coal releases sulphur and nitrogen Rainwater falls through these oxides in atmosphere This produces sulphuric and nitric acids Problem as poisons lakes and effects plant and animal growth

Oil Pollution Moved in vast tankers Old vessels are single hulled and when bumped vent their cargo

destroying Eco systems

Conserving resources

Fossil fuels are limited (they will run out)

This type of fuel is known as Non-Renewable or Finite

How can we save energy?

By using more energy efficient systems, such as light bulbs

Renewable Energy Sources

As fossil fuels will run out at some point we need to consider other energy sources.

Energy sources that come from daily sunshine are called renewable sources

These include solar power, wind energy, hydroelectricity and energy from the tides and waves

R e n e w a b l e E n e r g y

SOLAR

In its simplest form a water tank on the roof will heat up and provide hot water

Photovoltaic cells (contain crystals of silicon) convert light energy into electricity

Wind

Modern turbines placed in groups (wind farms) Production depends on wind strength and so

variable Also thought of as ugly on the landscape New idea is to place them in shallows of the

mainland and out of sight

More renewable...

HYDROELECTRIC

A controlled flow of water (head) allowed to flow through a turbine

Generates power

Large scale head produced with a dam

Small scale water tunnel with sluice gate

Wave

WAVE  Bobbing ducks generate power via turbines

Strung out in long lines either off or on shore

Tidal

Gravity from Sun/ Moon pulls tide into estuary

Dam/ barrier raised creates a head of water

Released through turbine

E n e r g y C a l c u l a t i o n s

Work Done

WORK DONE = FORCE X DISTANCE

Force in Newtons (N) Distance in metres (m) moved in the direction of the force Unit of work is Nm or Joules (J)

A winch raises a lift of mass 1000kg to a height of 20m.Calculate the minimum amount of work done by the winch

Weightlift = mg = 1000 x 9.8 = 9810N

Work Done (winch) = F x D = 9800 x 20 =

196kJ

WORK DONE (Pupil Problems)

Q1. During the loading process, a fork- lift truck lifts a pallet of bricks of mass 740kg up to a height of 2m. Calculate the minimum work done by the truck and suggest a reason why the actual work done will be greater.

Q2. A mass of 50kg is raised to a height of 5m by a rope, which is wound around a pulley on a motor shaft of diameter 150mm as shown. Determine the amount of work done by the motor and the number of revolutions made during the lift.

K i n e t i c E n e r g y

Name given to the energy a body possesses due to its motion

Depends on two things:

the mass (m) of the body (measured in kg) velocity (v) of the body (measured in m/s)

EK = ½ m v2

P o t e n t i a l E n e r g y

Energy stored in a static object

Depends on two things:

the mass (m) of the body (measured in kg) height (h) of the body (measured in m) above a set datum

EP = m g h

E l e c t r i c a l E n e r g y

Name given to the energy produced by power stations via turbines

Depends on three things:

the circuit current (I) measured in Amps voltage (v) of the circuit (measured in Volts) Time that the circuit has been operating (t) measured in

seconds

Ee = I t V

H e a t E n e r g y Energy transferred to a body that results in a

change in the body's temperature

Depends on 3 things:

Mass Specific Heat Capacity

Change in temperature

Eh = m c ΔT

Energy questions

1. When an Olympic diver stands on a diving board 10 m above the pool, what form of energy does he possess?

2. When the diver jumps on the diving board it will bend. What form of energy does the board now possess?

3. When the diver is at the highest point of his dive why does he not have any kinetic energy?

4. The diagram below shows a representation of a hydroelectric power station.

   

Name the form of energy at each of the stages A, B, C and D

TU R BIN E G EN ER ATO R M O TO R

DAMWATER

A

B C D

Energy questions

1. During a sheet-making process, 50 kg ingots of metal are passed along rollers at a speed of 0.5 m/s. Calculate the kinetic energy of each ingot.

2. A girl of mass 50 kg is riding on her bicycle and has a kinetic energy of 2.5 kJ. What speed is the girl moving at, and what is the kinetic energy of the bicycle if it has a mass of 30 kg?

3. An escalator has six people on it with a total mass of 900 kg. If the escalator moves at a uniform speed of 0.5 m/s, what is the average amount of kinetic energy that each person contains?

   

Energy questions

4. Baggage handlers at an airport, place suitcases on to a conveyor belt, which lifts them up to the hold of the aeroplane as shown. What is the potential energy of a case of mass 22kg at the top of the conveyor?

5. Metal piles are driven into the ground using a pile driver. The driver is raised to a height of 5 m above the ground and then released.Calculate the weight of the driver if the potential energy stored when it has been lifted is 9810 joules.

   

3.5m

Energy questions

6. If the amount of electrical energy used by a 110 V, 30 A d.c. motor is 1.98 MJ, for how long has the motor been in operation?

7. Calculate the heat energy required to heat 2 kg of water from a temperature of 20 ºC until it begins to boil.

   

Energy questions

8. The heating element in a shower can produce heat energy at a rate of 7 kJ/s. Water enters the system at a temperature of 15C and is heated to 40C. Estimate the flow rate (in litres per second) and state any assumptions you have made. (1 litre = 1Kg

57 kJ of thermal energy is supplied to 1.7 kg of oil having a specific heat capacity of 2.7 kJ/kgK. If the initial temperature of the oil is 3C, what will be its final temperature?