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The information below is intended to provide introductory material for elementary students and further material for high school students.

Please keep in mind that not all demonstrations are presented at each show, and each topic may not be covered.


ENERGY

Introduction

  • Energy can be neither created nor destroyed, but it can be converted from one form to another and it can be transferred from one object to another.

    The total amount of energy in an isolated system is constant, it can never change. But that energy is often changing form and being transferred. For example, when you eat breakfast in the morning, you are storing energy inside of you. Later on in the day, when you are walking or running, that stored energy is converting itself to the motion of you walking. Also, when you give someone a push on the swings, you are transferring the energy you have inside of you to the person on the swing. You can tell because that person goes higher and faster because he/she has more energy and you may become tired after awhile because you have less energy.


  • During a collision, energy is usually transferred from one object to another.

    When two objects interact with each other in a collision, each object exerts a force on the other object, and energy may be transferred.


  • Energy can be stored in an object by lifting the object to a certain height. This energy is called gravitational potential energy. The gravitational potential energy of an object depends on how heavy the object is and how high it is. The heavier an object is, the more gravitational potential energy it has, and the higher an object is, the more gravitational potential energy it has.

    Potential energy is stored energy. If an object is very heavy and is located at a certain height, it will have more stored energy than a lighter object at the same height. We know that this is true because which would you rather catch dropped from a building, a bowling ball or a tennis ball? Since the bowling ball is heavier than a tennis ball, it has more stored energy. This energy, while falling, is converted to the energy of motion, or kinetic energy. Secondly, the higher an object is, the more stored energy it will have. This can be shown by the fact that jumping off a chair is relatively harmless, but jumping off of a building is ill-advised. Since you are much higher on top of a building, you have much more energy than on top of a chair. This stored energy gets converted to kinetic energy as you fall. When you jump from the top of a building, the stored energy gets converted to so much kinetic energy, in fact, that your legs can no longer brace against the collision.


  • Energy can be stored in a spring. The potential energy of a spring depends on what the spring is made of and how far back the spring is pulled. The stiffer the spring, the more energy can be stored, and the further it is pulled back, the more energy is stored.

    Potential energy is stored energy. If a spring is made of a material which is very stiff, then it will have more potential energy than a spring made of a material which is less stiff. If two springs are pulled back the same amount, but one is made of a material which is stiffer than the other, then when the springs are released, the spring made of the stiffer material will recoil with more energy. Secondly, if a spring is pulled back really far, it will have more energy than if it is pulled back just a little bit. We know this because when we release a spring which has been pulled back really far, it recoils with more energy than a spring which is just pulled back a little bit.


  • A moving object has energy known as kinetic energy. The kinetic energy of an object depends on how massive the object is and how fast the object is moving. The more massive an object is, the more energy it has, and the faster an object is moving, the more energy it has.

    A massive object moving at a certain speed has more energy than a less massive object moving at the same speed. We know that this is true because it is very easy to stop a ball rolling down a hill but very difficult to stop a car rolling down a hill. Since the car is more massive, it has more energy. Secondly, an object moving very fast has more energy than the same object moving slowly. We know this is true because a bullet shot from a gun is very dangerous: it has enough energy to hurt someone. A bullet tossed from one person to another, however, is relatively harmless: it contains much less kinetic energy.


  • More Specifically

  • Energy can be neither created nor destroyed, but it can be converted from one form to another and it can be transferred from one object to another.

    The total amount of energy in an isolated system is constant. That energy, however, is constantly being converted from one form to another and is constantly being transferred from one object to another. When you drop a ball, for example, the ball's potential energy is converted to kinetic energy. The ball's total energy remains the same, however. In a different case, if you kick a ball, you are transferring some of your energy to the ball. The ball clearly has more energy: it is moving; and you have less energy: kicking the ball many times makes you tired.


  • During a collision, energy is usually transfered from one object to another.

    When two objects interact with each other in a collision, each object exerts a force on the other object, and energy may be transferred.


  • U = mgh, where U = gravitational potential energy, m = mass, g = gravitational constant, and h = height.

    As can be seen from the formula, the gravitational potential energy is directly proportional to both the mass and the height of an object. This means that the more massive an object, the more potential energy it has, and the higher an object, the more potential energy it has. Potential energy is stored energy. Since it takes more energy to raise a heavy object and more energy to raise an object higher, they will have more energy stored within them.


  • U = 1/2 kx2, where U = potential energy of a spring, k = spring constant of the material, and x = displacement.

    As can be seen from the formula, the potential energy of a spring is directly proportional to the displacement and to the square of the spring constant. This means that the larger the spring constant, the more potential energy, and that the greater the displacement, the more potential energy. The spring constant of a spring is determined by how rigid the spring is. The more rigid the spring, the larger the spring constant. The displacement is how far back the spring is pulled. The further the spring is pulled, the more energy is stored. The fact that the potential energy is directly proportional to the square of the displacement and not merely proportional to the displacement is an empirically determined result: many experiments resulted in this knowledge.


  • K = 1/2 mv2, where K = kinetic energy, m = mass, and v = speed.

    As can be seen from the formula, kinetic energy is directly proportional to the square of the speed and to the mass. This means that the more massive an object, the more energy it has, and the higher the speed, the more energy it has. Kinetic energy is the energy of motion. It takes more energy to get a massive object moving, and more energy to get an object moving very fast, so we know that they contain more energy.


  • Related Demos

    The following demonstrations illustrate this physics topic:

    Sponsored by the Physics Department and the Center for Science, Mathematics, and Engineering Education -- University of Virginia