Year 8 Physics Energy

Force

A push or pull between objects that may cause one or both objects to change speed and/or direction of their motion or change their shape.

Energy

The ability to do work.

Unit for force

The unit for force is the Newton (N).

Unit for energy

The unit for energy is joules (J).

1 joule

1 joule is roughly the amount of energy needed to lift an apple 1 metre off the ground.

1 kilojoule

1 kilojoule (kJ) is equal to 1000 joules.

Energy transfer

Energy transfer occurs when work is done; it is the movement of energy from one object or system to another.

Weight

The force exerted by gravity on an object.

Mass

The measure of the amount of matter in an object.

Power

The rate at which work is done or energy is transferred.

Unit for power

The unit for power is watts (W).

One watt

One watt is equal to one joule per second (J/s).

Work

Work is done when a force moves; it is a measure of energy transfer that occurs when an object is moved over a distance by an external force.

Work equation

Work = Force x distance.

Unit for work

The unit for work is joules (J).

Types of energy

If you have energy, you can do things; every living thing needs energy to survive.

Examples of energy use

Anything that moves or produces heat needs energy, e.g., cars, TVs, laptops, etc.

Forms of Energy

There are many different forms of energy.

Common examples of energy

Light, sound, and electrical energy.

Light energy

Can be seen when a lamp illuminates a room.

Sound energy

Can be heard when a wolf howls.

Electrical energy

Travels through electrical wires such as power lines.

Production of electrical energy

Produced by energy transfers at power stations and in batteries.

Categories of energy

Energy can be categorized into two broad topics: Kinetic energy and potential energy.

Kinetic energy

The energy of motion; the energy that an object possesses due to its movement.

Types of motion

Horizontal movement, vertical movement, vibration, rotation.

Abbreviation for kinetic energy

Kinetic energy can be abbreviated as KE.

Factors affecting kinetic energy

The object's speed and the object's mass.

Effect of speed on kinetic energy

Higher speed = higher kinetic energy; lower speed = lower kinetic energy.

Standard unit for speed

Metres per second (m/s).

Effect of mass on kinetic energy

Larger mass = higher kinetic energy; smaller mass = lower kinetic energy.

Standard unit for mass

Kilogram (kg).

Measuring kinetic energy

It's possible to calculate how much kinetic energy an object has if you know its mass and speed.

Effect of doubling speed on kinetic energy

When the speed of an object doubles, the object has four times the amount of kinetic energy.

Effect of doubling mass on kinetic energy

When the mass of an object doubles, the object has double the amount of kinetic energy.

Heat energy

Also called thermal or internal energy; energy that comes from the motion of atoms and molecules in a substance.

Heat transfer methods

Conduction, convection, and radiation.

Conduction

Occurs when two objects are in contact (solids); heat transfers from the hotter substance to the colder one.

Convection

Heat flows through liquids and gases (fluids).

Radiation

Heat radiates from a hot object, transferred as a wave that can travel even through the vacuum of space.

Light energy definition

A form of electromagnetic radiation of a wavelength that can be seen by the human eye.

Formation of light energy

Light energy is formed through the movement of photons, which are tiny packets of energy.

Use of light energy

Used by humans to see and by plants during photosynthesis to produce their food.

Electrical energy definition

Caused by the movement of electrons (negative electrical charges).

Effect of electron movement on electrical energy

The faster the charges move, the more electrical energy they carry.

Radiant energy

A form of electromagnetic energy

Potential energy

Energy that can be stored for later. An object possesses this stored energy due to its position or configuration.

Elastic potential energy

The energy stored in an object when it is deformed elastically. When an object is stretched, twisted or compressed within its elastic limit.

Elastic limit

The force beyond which the spring becomes permanently deformed.

Hooke's Law

An approximation of the response of elastic bodies. The extension of a spring is in direct proportion with the load applied to it.

Gravitational potential energy

The energy an object possesses due to its position in a gravitational field. It is the energy stored as a result of the object's height above the Earth's surface.

Chemical potential energy

Also known as chemical energy. It is the energy stored in chemicals, available in the chemical bonds of a compound.

Nuclear energy

Also known as nuclear potential energy. Nuclear energy comes from the nucleus of atoms and is released by nuclear fusion or nuclear fission.

Mechanical energy

The sum of kinetic energy (energy of motion) and potential energy (stored energy due to position).

Renewable energy

A natural resource that is replenished by natural processes within a human lifetime.

Energy transformation

When energy changes from one form to another.

Law of Conservation of Energy

Energy can neither be created nor destroyed, only converted from one form of energy to another.

Work done compressing or stretching a spring

If you have a linear equation/graph, then you can find the work by taking the area of the F-d graph.

Calculating elastic potential energy

The formula for calculating elastic potential energy is not provided in the notes.

Determining the spring constant

The spring constant can be determined from a force-displacement graph.

Chemical energy in food

In food, it can be measured in kilocalories (kcal). There are 4.2 kJ in 1 kcal.

Nuclear fission

Nuclear fission is when the nuclei are split apart.

Nuclear fusion

Nuclear fusion is when the nuclei are fused together.

Energy acquired by objects

The energy acquired by objects on which work is done can be either kinetic or potential energy.

Green energy

Renewable energy is also called green energy.

Flow diagrams

A visual model that shows the forms of energy involved and arrows to show energy transfers and transformations.

Thermal energy transfer example

When boiling water in a pot, thermal energy is transferred from the flame to the pot to the water.

Energy efficiency goal

An important goal is efficient conversion of energy.