The Two Types of Energy
The many forms of energy can be grouped into two main categories based on how they behave: kinetic and potential.
Kinetic energy is the energy of motion—of objects, substances, waves, atoms, molecules, and electrons. Kinetic energy takes these forms:
- Electrical energy, which moves through wires to power the lights, devices, and appliances in your home.
- Radiant energy, such as sunlight coming through a window, the light from your desk lamp, and the X-rays you might get on a trip to the dentist.
- Thermal energy, such as the heat that comes off a hot pan on the stove or the warmth generated by friction when rubbing your hands together.
- Motion energy, which is the movement of objects from one place to another.
- Sound energy, which is the movement of vibrations through a substance such as air, water, solid objects, or the ground.
Potential energy is stored energy that can be unleashed to create change or do work. Potential energy takes these forms:
- Chemical energy, which is in the batteries that run your devices, the gasoline that powers your car or truck, and the food your body digests.
- Stored mechanical energy, such as the energy in a stretched rubber band or a compressed spring in a ball-point pen.
- Nuclear energy, which is bound in atomic nuclei.
- Gravitational energy, which is the energy of position or place. A ball resting at the top of a ramp contains gravitational energy. Hydropower is another example of gravitational energy.
Kinetic energy can transform into potential energy and vice versa. For example, when a ball starts to roll down a ramp, its gravitational potential energy becomes kinetic. When the ball comes to a stop, its energy switches from kinetic back to potential. Can you see kinetic or potential energy at work around you right now?
Electricity Moves!
Electrical energy is kinetic energy because it comes from the movement of electrons through a conductor. Conductors are materials that allow electrons to move through them easily.
Electricity will flow through a conductor when an outside force—such as light, heat, pressure, or a chemical reaction—causes an electron to break free and get “bumped” from one atom to the next. A sequence of electrons then passes from atom to atom along the length of the conductor. This continuous flow of electrons from atom to atom through a conductor is called electrical current.
Copper, other metals, and water are excellent conductors because the electrons of their atoms are loosely attached, allowing electricity to travel through these materials easily. The human body is also a good conductor, so if you come into contact with electricity, it will move through your body and give you a harmful—or fatal—electrical shock. This is one reason it’s important to stay far away from power lines and to use electrical appliances, cords, and outlets safely.
Can you guess what makes the human body a good conductor for electricity?
Energy Can Transfer and Transform
Energy constantly transfers from one place to another.
For example, when a cat sits on a sunny windowsill, radiant energy from the sun moves through the window and heats up the cat’s fur.
A bicycle is another great example of this. When you ride a regular bicycle, chemical energy from the food you eat is converted by your body into mechanical energy that moves from your legs to the pedals. 
Energy from the pedals is transferred to the gears, which transfer it to the wheels to move the bike along. Something similar occurs when you ride an e-bike: Electrical energy is transferred from the motor to the gears and then to the wheels.
Energy also transforms from one form to another.
For example, when you switch on a flashlight, the chemical energy stored in the batteries gets converted into electrical energy. The electrical energy then changes into light energy and a small amount of thermal energy (heat). The energy keeps changing forms, but it doesn’t get created or destroyed.
The Law of Conservation of Energy explains that energy is never created or destroyed. It only changes from one place to another and from one form to another during all of its transfers and transformations. 
Can you think of some examples from your daily life where you observe energy being transferred from one place to another or changed from one form to another?
Energy Can Get Lost
When energy changes from one form to another, some energy always gets “lost.” It doesn’t disappear; it just takes another form—usually heat that we don’t want or need. For example:
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When you make toast, the toaster gets hot on the outside. That’s wasted heat energy. Materials with high resistance convert more electrical energy into heat. -
Your game console or phone gets warm when you use it. That’s electrical energy being lost as heat.
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Car and truck engines get super hot. That’s fuel energy being lost instead of all of it being used to move the vehicle.
When we say something is “energy efficient,” we mean it turns energy into what we actually want and loses less energy as heat. LED lights are more energy efficient than other types of light bulbs because they turn more electricity into light and less into heat. This allows them to use less electricity to make the same amount of light. Ask an adult in your household if you have any energy-efficient light bulbs or appliances at home.