Force can be a push or a pull. There are many different kinds of forces that we see everyday. For example, when you open the refrigerator door, you are using a force by pulling on the handle. When the wind blows, it is a strong force that can pull back on our clothing, or push our hair into our face. Some forces are small, and others are very big. Scientists that study forces are called Physicists. Physics is all about what things are made of, and how they move.
Forces can be indirect or direct. When a force is direct, one object touches another, or makes contact. You opening the refrigerator door is a direct force. Indirect force is like a magnet - it pulls on an object (like another magnet, or a paperclip or nail), even though it isn't touching that object. When you are riding a bike downhill, you might notice that you don't have to pedal as much. That is because an indirect force is pulling down on you and the bike. This force is called gravity. Gravity is a force that is always pulling. When you put a cup of water down on the table, it stays there because of gravity. When you jump on a trampoline, you come back down because of gravity. Gravity is such a big force that it controls the way our planet Earth moves around in an orbit, being tugged at by the sun.
When something has motion, it means that it is moving. Motion is caused by force. Not all forces cause motion! For example, if you tried pushing on the back of your family's car, you would be using force (push), but the car wouldn't move. An example of force that causes motion is riding a bicycle. When you ride a bike, you are pushing on the pedals, and they are connected to gears, which cause the wheels to turn. The bike doesn't move by itself. To be in motion, the bike needs to have you put force on it by pedaling. Because of the gears, a small force on the pedals works to make the bicycle move. Riding a bike is much easier than pushing it along the sidewalk. This is because of inertia (ih-ner-sha). Inertia is not a force, but it changes the way things can be pushed or pulled. The word inert means not moving. Inertia means that a heavy object requires more force to move, but once it is in motion, it will move farther. Next time you're at the grocery store with your parent, try this. See how easy it is to push an empty shopping cart compared to one that is full of groceries. But, once the heavier cart starts moving, you can let go of the handles and it will still move forward. The heavier object has more inertia.
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