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What Is Energy?
Energy describes the ability of an object to do work. Work is the transfer of energy that happens when an external force moves an object.
There are two main types of energy. They are kinetic energy and potential energy. Mechanical energy is the sum of the kinetic and potential energy in a system.
Energy is not a tangible thing. This can make it difficult for children and adults to grasp the concept. Energy describes an object’s ability to cause change or do work.
Kinetic Energy: The Energy of Motion
A moving object has kinetic energy. The faster it moves, the more kinetic energy it has. Sound, heat and electricity are all examples of kinetic energy.
Sound energy moves through substances in longitudinal waves. These waves have to travel through a medium like air or water. Sound waves are created when a force causes an object to vibrate. For example, a hand hitting a drum creates sound waves.
Thermal energy is another way of saying heat. It comes from the movement of atoms and molecules in matter. The faster the molecules move, the hotter the matter becomes. And the hotter the matter becomes, the more thermal energy it has. Think about boiling water on the stove. As the water heats up, its molecules move faster and faster.
Electrons are tiny charged particles. When they move, they produce electrical energy. Moving electrons carry energy through an electrical conductor. Any device that you have to plug into the wall runs on electrical energy.
Potential Energy: Stored Energy
Potential energy is stored in a stationary object. When the object moves, its energy changes from potential to kinetic. These objects all have potential energy:
- The water behind a dam
- A rock perched on the top of a hill
- Fireworks about to be launched
Chemical Potential Energy
Chemical potential energy is stored in the bonds of molecules. It gets released through a chemical reaction. Chemical potential energy usually produces thermal energy. For example, the natural gas burned in a furnace releases heat. Likewise, the energy stored in the food you eat gets released through digestion.
Gravitational Potential Energy
An object’s height and weight give it gravitational potential energy. The higher and heavier the object, the more gravitational potential energy it has. Think of water about to flow over a waterfall. The higher the waterfall, the more gravitational potential energy the water has.
You may think that an object at rest has no energy. An object at rest has no kinetic energy. But depending on its position, it will have a form of potential energy. When you hold a rock above the ground, it has gravitational potential energy. And the banana you ate for breakfast had chemical potential energy.
Mechanical energy is the sum of energy in a mechanical system. It includes both kinetic energy and potential energy. So objects have mechanical energy when they are in motion. And they also have it when they have the potential to move. A car moving down the highway has mechanical energy. And so does a book you hold up in the air.
The faster an object moves, the more energy it stores. This stored energy can be used to apply a force to another object. In other words, it does work on the object. Think of a wrecking ball demolishing a building. It has potential energy because it is held up in the air. As it swings toward the building, the energy is transformed into kinetic energy. Eventually, the ball comes in contact with a wall. That’s when the kinetic energy of the ball applies a force on the building, which can cause it to fall down.
Energy cannot be created or destroyed. It can only be changed into different forms. To demonstrate energy transformation, get children to rub their hands together. The rubbing is an example of mechanical energy. And the children can feel the heat as it gets converted into thermal energy.
Energy is everywhere and in every part of our lives. In fact, you can’t live without it! How would you survive without thermal energy from the Sun or chemical energy from the food you eat?