Human Anatomy Videos

Do you know that you are working when you are playing?

To a scientist, work is any kind of action that uses energy.

Energy is needed to do all types of work—for example, to throw a ball into the air and to catch it. Energy is needed because something does not move unless you push or pull it. And it doesn’t stop moving unless something else slows it down. When you catch a ball, your hand can feel the ball pushing to continue moving. Inertia is a basic characteristic of an object as it continues to stay at rest or continues to move.
If you want to start moving something or stop it from moving, you need to push or pull it. These pushes and pulls are called forces. Forces are needed to overcome inertia. Forces are produced by applying energy. The more force applied, the more energy used and the more work done.

Energy for lifting

When you lift a heavy box, potential energy changes to kinetic energy in your muscles. You use more energy and do more work when you move a heavy box than when you lift a lighter box for the same distance. You do more work when you lift a box up to a high shelf than when you lift it onto a low shelf. If you carry a pile of books weighing 22 pounds (10 kilograms) up a flight of stairs, you do twice as much work than if you carried an 11-pound (5-kilogram) pile up the same flight of stairs. Since work is equal to force times distance, the energy you use is equal to the weight of the books times the distance you moved.

• How do you keep cool in your house?

• What sort of light do you use at night?

• What appliances do you have in your home?

  Anything that gives you heat or light uses energy.

Household appliances use energy. In your notebook, make a list of all the things in your kitchen that use energy. What kind of energy do you think each appliance uses?
Most homes receive a supply of electricity. The electricity travels along cables and wires from a power station. At the power station, electricity is usually made from the energy released by burning fossil fuels, or by using nuclear fuel or waterpower.
Fossil fuels developed from the remains of prehistoric plants and animals. 
These fuels include coal, natural gas, and petroleum, from which we get oil. Wood, also, is often classified as a fossil fuel.
Besides electricity, fossil fuels are also used as a source of energy in our homes. Wood, coal, and oil can be burned to give heat. Natural gas can be burned for heating and cooking. Oil lamps and gasoline lanterns can be used as a source of light.
Other sources of energy in the home include solar energy and wind power.
Solar energy is energy from the sun, often gathered by solar panels. Solar energy can warm a house or heat up water. Wind power is often impractical unless there are strong, steady winds.

Fossil fuels are called nonrenewable sources

- of energy because, once they have been used up, they cannot be replaced. One day, all the coal, natural gas, and oil on earth may be used up. There will then be no more available.

Sources of energy that can be used over and over again are called renewable, or inexhaustible, sources.

Solar energy and forms of solar energy, like wind power and water power, are renewable energy sources. No matter how much we use them, there will always be plenty more.