This is an introduction to basic physics for elementary age kids and homeschoolers. It covers direct, indirect, and balanced forces as well as gravity, magnetism and friction.
When you kick a ball, the force of your kick makes the ball move. When you pull a wagon, you are applying a force that makes the wagon move. Think of a force as a push or a pull. Forces can make things move, speed up, slow down and change direction.
A force called gravity keeps you from floating into space. A force called magnetism can hold a grocery list on your refrigerator. Friction is a force that can slow you down.
Direct, Indirect and Balanced Forces
A direct force involves touching. When you push a friend on a swing, you are applying a direct force. When you pull open a fridge door that is also a direct force. Direct forces are also called contact forces.
Distant forces don't involve touching. If you jump up, gravity pushes down on you and pushes you back to the ground. Magnetism is also a distant force. Distant forces are also called long range forces or noncontact forces.
When something isn't moving, the forces acting on it are said to be balanced. The forces pushing or pulling an object in one direction are the same as the forces pushing or pulling it in the opposite direction.
Learn About Gravity
Every object has a gravitational pull. The larger an object is the greater the gravitational pull. The moon is smaller than the Earth. If you were on the moon you could jump much higher than you could on Earth because the gravitational force pulling you down is smaller. The gravitational pull of a large planet like Jupiter is so strong, you would be unable to move.
Have you ever wondered why the moon orbits Earth rather than floating away? Or why the moon doesn't crash into the Earth? This is gravity at work. The Earth is continuously pulling the moon toward it but the moon is constantly trying to fly away in a straight line. An orbit is the result.
Learn About Magnetism
Magnetism is a distant force that can act on metal. A magnet is a piece of iron that can pull some types of metal toward it. It's a distant force because it can pull metal toward it without directly touching it. The area around a magnet where the force of magnetism acts is called a magnetic field. If you move a piece of metal outside of a magnetic field, the magnet will no longer be able to pull on it.
A magnet has poles called a north pole and a south pole. This probably sounds familiar to you. The Earth is magnetic and surrounded by a magnetic field. The North Pole and South Pole on Earth are magnetic poles. It is the north magnetic pole that pulls the needle on a compass toward the north.
North poles and south poles on magnets pull toward each other. This is called magnetic attraction. If the poles are the same, the two magnets will push each other away. So, you can't join together the south poles on two magnets. They won't ever touch. This is called magnetic repulsion.
Learn About Friction
If you try to slide on grass, you won't get too far. However, when you slide on ice, you move easily. This is because grass creates more friction than ice. Friction is a type of force that can slow things down.
Friction is caused by two things gripping each other. The rougher a surface is the more friction it will create. This is why you can't slide easily on grass but you can on ice. Look at the bottoms of your shoes. They have grips that prevent slipping on smooth floors.
Friction can create heat. Rub your hands together quickly. The friction between your hands will create heat.
Cars and planes are designed to move as easily as possible through air. Boats are designed to move as easily as possible through water. This is called streamlining. When things move through air or water, they encounter friction. Streamlining reduces its effect.