Energy Transfer

Electricity flows through circuits. A simple circuit needs a power source, a conductor (wire), and a load (like a light bulb). Breaking the circuit stops the flow of electricity.

Electromagnets are temporary magnets created by running electricity through a coiled wire. They can be turned on and off and are used in motors, speakers, and MRI machines.

Kinetic energy is the energy of motion. A moving car, a rolling ball, and a flying bird all have kinetic energy. The faster an object moves, the more kinetic energy it has.

Potential energy is stored energy based on position or condition. A ball at the top of a hill has gravitational potential energy. A stretched rubber band has elastic potential energy.

Magnets have north and south poles. Opposite poles attract and like poles repel. The magnetic field is strongest at the poles and gets weaker with distance.

Static electricity builds up when objects gain or lose electrons through rubbing. Rubbing a balloon on your hair transfers electrons, making the balloon stick to a wall.

Energy can be transformed from one form to another but cannot be created or destroyed. A light bulb converts electrical energy into light and heat energy.

Renewable energy sources like solar, wind, and hydroelectric power can be replenished naturally. Nonrenewable sources like fossil fuels take millions of years to form.

Mass is the amount of matter and is measured in kilograms. Weight is the pull of gravity on that mass and is measured in newtons. On Earth every kilogram weighs about 10 N; on the Moon it weighs less than 2 N.

Gravity does not stop at the ground. It reaches out from Earth far enough to hold the Moon in orbit, and out from the Sun far enough to hold every planet. The further away you go, the weaker it gets.

Astronauts on the space station are not beyond gravity — it is still about nine tenths as strong there as at the surface. They float because they and their spacecraft are falling around the Earth together, and everything falls at the same rate.

Drop a heavy ball and a light one together and they land together, because gravity gives every object the same acceleration. Only air resistance changes this, which is why a feather is the exception rather than the rule.