Energy

nergy is the ability to do work. In science and engineering, work is done when a force moves an object. The work done to move an air­craft requires energy.

Forms of Energy

There are many different forms of ener­gy. Everything that moves has energy; the energy of movement is called kinet­ic energy. The more massive something is and the faster it moves, the more kinetic energy it has. Something can also have energy because of its position or condition. This is potential energy, or stored energy.

There are different types of potential energy. If a ball is taken up to the top of a hill, work has to be done to move the ball upward against gravity. The ball
thereby acquires gravitational potential energy. The energy stored in a squashed spring is known as elastic potential energy. The type of energy stored in chemicals, including aircraft fuel and rocket fuel, is chemical potential energy.

Kinetic energy and potential energy are both types of mechanical energy. Other forms of energy include heat ener­gy, electrical energy, magnetic energy, light energy, nuclear energy, and sound energy. Heat energy is also called ther­mal energy, and light energy from the Sun is called solar energy.

Energy cannot be created or destroyed. It can only be changed from one form to another. If a ball taken up to the top of a hill is allowed to roll down the hill, its potential energy changes to kinetic energy. If a squashed spring is released, its potential energy changes to kinetic energy. Burning a fuel changes

О This diagram shows how potential energy can turn to kinetic energy when a ball is pushed up a hill and then rolled downward. The ball stores potential energy acquired on the upward journey that is released as kinetic energy on the way down.

WHERE DOES A GLIDER’S ENERGY COME FROM?

Gliders have no engines, so they need to get their energy from another source. Gliders are towed into the air by a cable pulled by a plane or by a winch on the ground. When the cable is released, the glider has a certain amount of energy-part – ly kinetic energy because of its movement and partly gravitational potential energy because of its height. When a glider dives toward the ground, some of its potential energy changes into kinetic energy, and it speeds up.

Energy can be changed in the opposite direction as well. When a pilot makes a glider climb, the aircraft’s kinetic energy changes back into potential energy. In still air, a pilot cannot make a glider climb back up to the same height that it started from, because it loses energy to the surrounding air. The only way a glider pilot can avoid sinking slowly to the ground is to find a new supply of energy. When a glider flies into rising air, it gains potential gravitational energy as the air carries it upward. Then it can convert this into kinetic energy all over again.

its chemical potential energy to heat energy and light energy.

If all the different forms of energy are added up, the total is always the same. When a ball rolls down a hill, the sum of its potential energy and kinetic energy at every instant during its roll stays the same. This is also called the law of conservation of energy. An air­craft is more complicated than a rolling ball, but it follows the same law.