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.

The wind has been a source of energy for thousands of years.
Before the development of the steam engine, most ships relied on wind power to fill their sails and push them along. Windmills were used to turn grindstones and pump water.
Now scientists are turning to wind power again. This time they are using it to generate electricity.
Windmills have been used to produce electricity since the early 1900’s. It is easy to produce electricity from a wind turbine. This is simply a windmill that converts the kinetic energy of the wind into electricity.
Small wind turbines are used by farmers in remote parts of Australia and North America. In wide, open spaces, these turbines can make some of the electricity that farmhouses need. However, the winds are sometimes so strong that they damage the turbines and put them out of action.
Engineers have designed many different kinds of wind turbines to try to solve this problem. Some turbines look like old-fashioned windmills, with four blades, or sails. Other, more modern ones have two blades like those of an aircraft propeller.

In North America, this type of traditional windmill is used to pump water.

One of the largest wind turbines in the world stands in Hawaii, in the Pacific Ocean. It has two blades 165 feet (50 meters) long on top of a high tower. There is a smaller turbine on Orkney, off the coast of Scotland. It can generate enough electricity for about 1,000 homes. Most wind turbines are mounted on a cap, or swivel, on top of a tower. This means that they can be turned to face the wind when its direction changes.
A huge power station driven by wind has been built in the Mojave Desert in California. Its owners call it a “wind farm.”  Hundreds of wind turbines are arranged in rows and all are linked together by wires. The electricity they produce is supplied to the California power pool.
These wind turbines supply electricity to homes and factories.