Force

A force is a push or a pull. Forces make things move, stop, speed up, slow down, or change direction. Every time you kick a ball, open a door, or pick up a backpack, you are using a force. Forces are one of the most basic ideas in physics, the science of how the world works.

Forces come in two main types. A contact force happens when two things touch. Pushing a shopping cart is a contact force. So is a baseball bat hitting a ball. A non-contact force works across empty space, without anything touching. Gravity pulls you toward Earth even though Earth is not touching you. A magnet pulls on a paper clip from an inch away. Non-contact forces can feel a bit like magic, but they follow strict rules.

In the 1680s, an English scientist named Isaac Newton wrote down three rules about forces. These rules still work today. The first rule says an object will keep doing what it is doing unless a force changes it. A ball rolling on the floor keeps rolling until friction slows it down. The second rule says a bigger force makes something speed up faster. It also says heavy things are harder to push than light things. The third rule says every force has an equal force pushing back. When you jump, you push down on the ground. The ground pushes up on you with the same strength, and that is what launches you into the air.

Forces often work in teams, and sometimes they fight each other. When you sit in a chair, gravity pulls you down. The chair pushes you up with the same amount of force. The two cancel out, so you stay still. This is called balanced forces. When forces are unbalanced, something moves. A tug-of-war shows this well. If both teams pull with equal strength, the rope stays in place. If one team pulls harder, the rope slides their way.

Forces are everywhere, even when you cannot see them. The Moon stays in orbit because gravity from Earth keeps pulling it close. Airplanes fly because the air pushes up on their wings harder than gravity pulls them down. Even your beating heart uses force to squeeze blood through your body. Once you start looking for forces, it becomes hard to find anything in the universe that does not use them.