Energy transfers conservation and dissipation.pptx

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Energy transfers, conservation and dissipation

Energy

Lesson 5 of 7

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Warm-up

Energy

Lesson 5 of 7

Answer each one, then check.

1

Can energy be destroyed?

2

What is friction?

3

Name a good thermal insulator.

4

What is wasted energy?

5

Which store increases when friction acts?

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Energy

Lesson 5 of 7

1

Can energy be destroyed?

No

2

What is friction?

A force opposing motion between surfaces

3

Name a good thermal insulator.

Wool, foam or fibreglass

4

What is wasted energy?

Energy transferred to stores that are not useful

5

Which store increases when friction acts?

Thermal

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Learning Objectives

Energy

Lesson 5 of 7

1

Describe energy transfers in a closed system.

2

Explain how energy is dissipated.

3

Explain ways of reducing unwanted energy transfers: lubrication and thermal insulation.

4

Describe how thickness and thermal conductivity affect the rate of cooling of a building.

5

Describe an investigation into insulating materials.

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Energy

Lesson 5 of 7

DISSIPATION

Energy is never lost: it is transferred usefully, stored or dissipated. In every change some energy is dissipated into less useful stores.

The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction through it.

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Investigating Insulation (Required Practical 2)

Energy

Lesson 5 of 7

Only the insulating material should change.

Different insulating materials are compared by how slowly hot water cools inside them.

WHAT TO NOTICE

Insulated beaker

The material surrounds the beaker of hot water.

Control

An identical beaker with no insulation to compare against.

Thermometer and stopwatch

Record the temperature at regular times.

Fair test

Same volume, starting temperature, lid and beaker size.

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Reducing Unwanted Energy Transfers

Energy

Lesson 5 of 7

Lubrication

Oil between moving parts reduces friction, so less energy is dissipated to the thermal store.

Thermal insulation

Materials with low thermal conductivity, like foam and wool, reduce the rate of heat transfer.

Thicker walls

A thicker layer means a lower rate of energy transfer through it.

Lower conductivity

Walls made of material with lower thermal conductivity cool more slowly.

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A House Cooling

Energy

Lesson 5 of 7

Explain how the thickness and thermal conductivity of a house's walls affect its rate of cooling.

1

Thickness

Thicker walls slow the transfer of energy from inside to outside, so the house cools more slowly

2

Conductivity

Walls of lower thermal conductivity give a lower rate of energy transfer

3

Together

Thick walls made of a low-conductivity material give the lowest rate of cooling

ANSWER

The rate of cooling decreases with thicker walls and with lower thermal conductivity.

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Required Practical 2: Method

Energy

Lesson 5 of 7

Compare insulating materials.

1

Set up

Put a beaker of hot water inside a larger beaker with the insulating material packed around it.

2

Same start

Use the same volume of water at the same starting temperature (about 80 °C) for each material.

3

Measure

Record the temperature every minute for 15 to 20 minutes.

4

Repeat

Repeat with other materials and a control with no insulation.

5

Compare

Plot cooling curves. The smallest temperature fall shows the best insulator.

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Control Variables

Energy

Lesson 5 of 7

Make it a fair test.

Independent variable

The type of insulating material (or its thickness).

Dependent variable

The temperature drop, or the time to cool by a set amount.

Control

Volume of water, starting temperature, beaker size, lid, room temperature.

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Key Terms

Energy

Lesson 5 of 7

Dissipated

Transferred to the surroundings and stored in less useful ways.

Thermal conductivity

How well a material conducts thermal energy.

Insulator

A material with low thermal conductivity.

Lubrication

Using oil or grease to reduce friction.

Closed system

A system where no energy enters or leaves.

Control variable

A variable kept the same in a fair test.

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Energy

Lesson 5 of 7

YOUR TASK

Insulate the Cup

15 minutes

You have four cups, cotton wool, foam, newspaper and bubble wrap. Plan a fair test to find the best insulator, listing what you keep the same.

1

State what you change.

2

State what you measure and keep the same.

WHAT A GOOD ANSWER SHOWS

Independent: material. Dependent: temperature fall in 10 minutes. Control: volume and starting temperature of water, cup and lid, thickness of material, room conditions. Repeat and find a mean.

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Can I...?

Energy

Lesson 5 of 7

Explain energy conservation.

Explain dissipation.

Give ways to reduce unwanted energy transfers.

Explain lubrication.

Link thermal conductivity to rate of transfer.

Describe Required Practical 2.

Name control variables.

Read cooling curves.

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Summary & Exam Focus

Total energy is conserved.

Energy is always dissipated to the surroundings.

Lubrication reduces friction; insulation reduces heat loss.

Low thermal conductivity means slower heat transfer.

EXAM FOCUS

A student compares three insulating materials by measuring how quickly hot water cools. Describe how to make the test fair. (3 marks)

Name what you change, measure and keep the same.

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