Energy transfers

Chapter 16Physics

Energy transfers and transformationsWe are living at this moment due to the energy

transfers in our body.

As energy is transferred, it is transformed (changed).

Chemical energy in the food is transformed to movement (kinetic) energy when you raise your hand.

Chemical energy is also transformed into heat energy to keep you warm.

How energy use has increased?

Long ago needed enough stored chemical energy to people move around and find food.

If they could not find enough food and store it as chemical energy for later use, they simply starved to death.

In time people came to live together in groups and developed machines to make their life easier.

Energy transfer diagrams

Energy transformations can be shown by energy transfer diagrams.

There are 3 parts to an energy transfer diagram:1) An arrow showing the energy input.2) A box showing an energy converter or transducer.3) Arrows showing energy output.

Examples of energy transfer diagrams

Stored chemical energy

Catapult Kinetic energyStrain energy

Light and heat energyBunsen burner

a) Releasing a catapult

b) Burning gas in a Bunsen burner

Light energy

Balloon strain energyKinetic energy

Chemical energyCamera

c) Blowing up a balloon

d) Taking a photograph

Sankey diagramsA second kind of diagram that shows energy changes.

It shows arrows of different widths.

The width of the arrow represents the amount of energy.

The unit of energy and work is the Joule (J).A thousand Joule (1000 J) = 1 kJ (kilojoule)

Plants and energy- When a seed germinates, the tip

of the root pops out. (Energy stored inside the seed is used)

- Stored energy is also used by the growing shoot.

- The shoot grows up through the soil and uses energy from the seed as it sends out leaves.

- Some of the light energy falling on the leaves is trapped.

- It is converted into chemical energy as the plant makes food (Photosynthesis).

- The chemical energy stored in plants is transferred to a herbivorous animal when it eats it.

- The herbivorous animal then has a store of chemical energy, which it uses to keep itself alive and to move about.

- Carnivorous animals feed on herbivorous animals and take in stored chemical energy.

Energy and ourselves

What happens when the fat drops through the grill?

- If you do not take care while barbecuing the meat will catch fire.

- The meat and fat burn because they contain chemical energy (all food do).

- If you look at food packets, you will find an information box. It tells you about the ingredients used and nutrients present.

- Units used to measure energy in food is J and kJ.

- Energy in food is released through respiration process.

1 J = 0.24 calorie

Generating electricity- Electrical energy is a very

useful form of energy because it is easy to generate and transport.

- Michael Faraday (1791 – 1867), an English physicist, discovered could be made to flow in a wire if the wire was made to move through a magnetic field.

- A bicycle dynamo is an electrical device which can be located in the hub of a wheel (hub dynamo)

- The dynamo can be also clamped onto a bicycle frame close to a tyre (bottle or sidewall dynamo)

Inside a bottle or sidewall dynamo

When the dynamo wheel is in contact with the tyre it rotates as the bicycle wheel turns, the magnet turns and its field sweeps

through the tyres generating electricity which lights up the lamp.

Power station generator

- Inside a power station, there is a generator consisting of a huge electromagnet surrounded by coils of wire.

- The electromagnet is attached to turbine blades.

- When the turbine is made to spin the electromagnet spins producing an electric current in the coils

- In about 2/3 of the world’s power stations, water is heated to make steam (in a boiler)

Electrical energy(produced)

Heat energy(Heats the water)

Kinetic energy(Water to gas)

Chemical energy(Coal)

Kinetic energy(gas moves turbine)

Energy transfers in a power stationBurn it

Conservation of energy