Energy

• Energy is a quantity that measures the ability to cause change in an object or system.

We get energy from the changes in food when it is digested and stored in the body.

Energy• The unit of measurement for energy is the

joule (J).

• One joule is the energy needed to push with a force of 1 newton over a distance of 1 meter.

Systems and variables

• A system is a group of objects and the factors that affect these objects.

• In the car and ramp system color, light and friction were not included in the system.

What factors were included in the car and ramp system?

Systems and variables

• A factor that affects a system is called a variable.

Can you name these five variables?

Systems and variables

• You may change the system later to include new objects, effects, or variables such as friction.

Energy in systems• Energy is a measure of a system’s ability to

change or create change in other systems.• Energy is an important variable in all systems.

The energy the car has due to height can be compared on a ramp.

Kinds of energy

• Energy appears in many forms, such as heat, motion, height, pressure, electricity, and chemical bonds between atoms.

• Energy can transfer from one form to another.

Law of conservation of energy

• The idea that energy converts from one form into another without a change in the total amount is called the law of conservation of energy.

A bow and arrow transform energy from the stretched bow to the motion of the arrow.

Energy transformation

• The marble and the track are a system. • This system has two major kinds of energy

called potential energy and kinetic energy.

Energy transformation

• Potential energy is energy due to position.• When you lift the marble off the ground it gets

potential energy because of its height.

Energy transformation

• As the marble moves down the track, it loses potential energy.

• Potential energy is converted into kinetic energy, which is the energy of motion.

Energy transformation

• The marble slows down as it goes uphill because kinetic energy is being changed back into potential energy.

Energy transformation• Conservation of energy says the total energy stays

the same as the marble moves up and down.• The marble has the most kinetic energy when its

speed is greatest.

Energy in your life

• A joule is a tiny amount of energy compared to what you use every day.

• Some units of energy that are more appropriate for everyday use are the kilowatt-hour, food calorie, and British thermal unit.

Conserving Energy

• When you “use” energy by turning on a light, you are really converting energy from one form (electricity) to other forms (light and heat).

Conserving Energy• Electric power plants don’t make electrical energy. • Energy cannot be created. • Energy CAN be converted from other forms of

energy such as chemical, solar, or nuclear energy.

Conserving Energy

• An average electric power plant puts out 1,000,000 kWh of electrical energy per hour.

• That means 120 power plants are burning up resources each hour just to run light bulbs!