Year 8 Science — Energy, Heat Transfer and Energy Transformations

Atomic recall cards covering energy as the capacity to do work, the joule, forms of energy, transfers vs transformations, gravitational potential and kinetic energy equations, the Law of Conservation of Energy, open and closed systems, conduction, convection and radiation, plus practical variables, graphing rules and scientific diagram conventions. 118 cards. Gravity taken as 10 m/s² in calculations.

Energy is defined as the capacity to do what?

Do work, or cause a change in matter

Work is done whenever a force does what to an object?

Moves it, or changes its state

What is the SI unit of energy?

The joule (J)

What is the symbol for the joule?

J

How many joules are in one kilojoule?

1000 J

One joule is the work done when a force of one newton acts over what distance?

One metre

One newton is the force needed to accelerate a mass of one kilogram at what rate?

One metre per second squared

Energy that an object has because of its motion is called _______ energy.

Kinetic

Energy stored in an object because of its height above the ground is called _______ potential energy.

Gravitational

Energy stored in a stretched or compressed spring is called _______ potential energy.

Elastic

Energy stored in a substance and released during a chemical reaction is called _______ potential energy.

Chemical

Energy released when the nuclei of atoms join or split is called _______ energy.

Nuclear

What single word describes energy that is stored rather than being used to move something?

Potential

Which type of energy does a mountaineer standing on a summit possess?

Gravitational potential energy

Which type of energy is stored in the springs of a trampoline?

Elastic potential energy

Which type of energy is stored in food?

Chemical potential energy

Which type of energy is stored in petrol?

Chemical potential energy

Which type of energy is stored in a strip of magnesium ribbon before it burns?

Chemical potential energy

Which type of energy is carried by music?

Sound energy

Which type of energy does a leaf gain as it falls?

Kinetic energy

Which type of energy does a falling leaf still store because it is above the ground?

Gravitational potential energy

Which type of energy does whistling wind carry in addition to kinetic energy?

Sound energy

Radiant energy from the Sun arrives as light and which other form?

Heat energy

An energy _______ occurs when energy moves from one object or place to another without changing form.

Transfer

An energy _______ occurs when energy changes from one form into a different form.

Transformation

A hot stove warming a pot of soup is an example of energy transfer or transformation?

Transfer

A battery powering a torch bulb is an example of energy transfer or transformation?

Transformation

What is the equation for gravitational potential energy?

Potential energy = mass x gravity x height

In the potential energy equation, what does the symbol m stand for?

Mass

What unit must mass be in before it is used in an energy equation?

Kilograms

In the potential energy equation, what does the symbol h stand for?

Height above the zero energy point

What unit must height be in before it is used in the potential energy equation?

Metres

What quantity does the symbol g represent in the potential energy equation?

Acceleration due to gravity

What is the unit of acceleration due to gravity?

Metres per second squared

What is the accepted value of acceleration due to gravity on Earth?

Approximately 9.8 metres per second squared

What value of gravity is used in this unit to simplify calculations?

10 metres per second squared

Convert 2 tonnes into kilograms.

2000 kg

Convert 300 grams into kilograms.

0.300 kg

Convert 50 centimetres into metres.

0.50 m

Why does a car travelling along a flat road have zero gravitational potential energy?

Its height above the ground is zero

Does the speed of an object affect its gravitational potential energy?

No

Calculate the potential energy of a 2.5 kg rock on a 40 m cliff, using gravity as 10.

1000 J

Calculate the potential energy of a 5.0 kg brick on a 2.0 m wall, using gravity as 10.

100 J

Calculate the potential energy of a 40 kg student 3.0 m up a ladder, using gravity as 10.

1200 J

If the height of an object is doubled, what happens to its gravitational potential energy?

It doubles

What is the equation for kinetic energy?

Kinetic energy = half x mass x velocity squared

In the kinetic energy equation, what does the symbol v stand for?

Velocity

What is the unit of velocity in the kinetic energy equation?

Metres per second

Which quantity in the kinetic energy equation is squared?

Velocity

If the velocity of an object is doubled, what happens to its kinetic energy?

It becomes four times larger

If the mass of an object is doubled at the same speed, what happens to its kinetic energy?

It doubles

How much kinetic energy does a stationary object have?

Zero

Calculate the kinetic energy of a 400 kg car moving at 30 metres per second.

180 000 J

Kinetic energy calculations require you to know the object's _______.

Velocity

Potential energy calculations require you to know the acceleration due to _______.

Gravity

Which unit tells you a value is an acceleration rather than a velocity?

Metres per second squared

State the Law of Conservation of Energy.

Energy cannot be created or destroyed, only changed from one form to another

According to the Law of Conservation of Energy, how does the total energy of a system change during a transformation?

It does not change

A lamp is supplied 100 J of electrical energy and gives out 10 J of light. How much energy is wasted as heat?

90 J

What name is given to the energy transfer that does the job we actually want?

The useful transfer

Wasted energy is usually transferred to the surroundings as which form?

Heat

Why is wasted heat energy difficult to reuse?

It becomes too spread out

What is the equation for mechanical energy?

Mechanical energy = kinetic energy + potential energy

An _______ system can exchange both energy and matter with its surroundings.

Open

A _______ system can exchange energy but not matter with its surroundings.

Closed

Is an uncovered pot of boiling water an open or a closed system?

An open system

Placing a tightly fitting lid on a boiling pot makes it approximate which type of system?

A closed system

Which method of heat transfer moves energy through vibrating, colliding particles that stay in place?

Conduction

In which state of matter does conduction occur best?

Solids

Why are metals excellent conductors of heat?

Their free moving electrons carry the energy quickly

Why is conduction slow in non metals?

They have no free electrons

Which method of heat transfer involves the actual movement of a heated fluid?

Convection

Convection can only occur in which two states of matter?

Liquids and gases

What single word describes liquids and gases together?

Fluids

Why does a heated part of a fluid rise?

It expands, becoming less dense

What happens to the density of a fluid as it cools?

It increases, so the fluid sinks

What name is given to the circular path followed by heated and cooling fluid?

A convection current

Why can convection currents not form in solids?

The particles are held in fixed positions and cannot flow

Which method of heat transfer uses infrared waves?

Radiation

Which method of heat transfer requires no particles at all?

Radiation

Which method of heat transfer can travel through the vacuum of space?

Radiation

Which method of heat transfer allows us to feel the Sun's heat from 150 million km away?

Radiation

Which surface colour and finish is the best absorber and emitter of infrared radiation?

Matt black

Which surface colour and finish is the poorest absorber and emitter of infrared radiation?

Shiny silver

In the burning food experiment, what is the independent variable?

The mass of the snack burned

In the burning food experiment, what is the dependent variable?

The temperature rise of the water

Name one variable controlled in the burning food experiment.

The volume of water used

How is the temperature rise of the water calculated?

Final temperature minus initial temperature

How many joules are needed to raise the temperature of 10 mL of water by one degree Celsius?

42 J

How is the energy transferred to 10 mL of water calculated from the temperature rise?

Multiply the temperature rise by 42

The water in the burning food experiment rises by 8 degrees Celsius. How much energy was transferred?

336 J

How is the energy per gram of a burnt snack calculated?

Divide the energy transferred by the mass burned

Why is the measured energy always lower than the value on the nutrition label?

Energy is lost to the surroundings and combustion is incomplete

Name one improvement that makes the burning food experiment more accurate.

Stirring the water so the temperature is even

Why should a thermometer be read at eye level?

To avoid parallax error

Which variable is plotted on the horizontal axis of a science graph?

The independent variable

Which variable is plotted on the vertical axis of a science graph?

The dependent variable

Where are units written on a graph axis label?

In brackets after the label

What is the minimum fraction of the graph paper your scale should fill?

Two thirds

What should be drawn through plotted points that follow a straight trend?

A single line of best fit