Gravity keeps us all on the surface of the Earth. Without gravity's constant pull, we would never even have existed, because the Earth was only formed as a result of gravity pulling space debris together. Gravity can be taught in many ways, but starting at a simple level can help children grasp the concepts. Explain that all bodies of matter in the universe have their own gravity. The Earth's gravity, as a planet, is quite strong, due to its size. Smaller astrological bodies, such as the Moon have less gravity, so if you were to walk on the Moon, you would float and bounce as opposed to walking. Use examples, such as the orbits of the planets to help the children understand how much gravity affects the universe.
Magnetism is another important force in physics and it is also closely related to electrical energy. Magnets have two poles, the north and south poles. Explain that the Earth also has north and south poles, which is the reason compasses point north. Opposite poles attract one another, and equal poles repel one another. Give the children bar magnets if you have any available to allow them to fully understand this. Use online games, such as the BBC's "MI High: Magnets" game to help children gain a full understanding of magnetism. The game requires the player to save an object from being stolen with the use of magnets of opposing polarities.
Electricity is a form of energy which is strongly related to magnetism. Explain to the children that atoms, which make up all known things in the universe, contain electrons and protons. Protons rest within the nucleus of the atom and cannot escape, but the electrons move in orbit around the outside of the nucleus. Explain that electricity is the movement of negatively charged electrons to positively charged regions. Use lightning as an example of electricity in action. When a lot of electrons accumulate and move quickly, this causes a spark of lightning. Use a Van de Graff generator to show the children an example of this reaction if you have one.
Many different aspects govern the forces that control motion. Newton's three laws of motion can be taught to children at an early age and using games and demonstrations can help to cement these ideas in the children's minds. Newton's first law of motion states that if no forces are acting upon an object, a stationary object will remain as such and a moving object will continue moving at the same rate. The second law of motion states that force equals mass multiplied by acceleration and the third law of motion states that each action has an equal and opposite reaction. Use a game, such as "Forces in Action" to show how mass affects the distance an object will travel. Explaining centrifugal force can also give the children a better understanding of the forces that affect motion.