67 Force and Motion-High

Force and Motion Written by Ned Jensen

Introduction Each word above describes how objects can move. Some things move in a straight line, such as a ball rolled to you along the ground. When you kick the ball into the air, it flies in a curved path and then bounces on the ground until it stops. A merry-go-round revolves in circles, while lightning strikes in a jagged path. Motion is everywhere, and it's vital to life. Think of how your heart's movement keeps blood flowing throughout your body! In this book, you will learn what makes things move, stop, change direction, and change speed.

Motion Needs a Force In order to make something move, a force is required. Lifting, pushing, and pulling are all types of forces, and those forces come from countless sources. Sometimes a person can provide the force. If you lift a stack of books, push a broken-down car, or pull on a rope in a tug-of-war game, you are the source of a force.

Machines can also produce a force to move objects. The power of a huge engine can produce enough force to propel a massive rocket into space. A car's smaller engine makes its wheels spin, moving the vehicle down a road. Motors in cake mixers, fans, and blenders use electrical force to make things move. Nature can act as a force, too. For example, breezes make leaves dance in the treetops. Ocean waves make boats bob up and down. Forces deep underground can cause earthquakes that make the ground tremble and destroy buildings, bridges, and highways.

The Laws of Motion Much of what we know about motion comes from experiments and observations made by scientists hundreds of years ago. The Englishman Isaac Newton is especially famous in this regard. You may have heard of him as the man who was sitting under a tree when an apple fell and hit him on the head. The story goes on to tell how this event led to his theory about gravity, the invisible force that causes things to fall toward the ground. Actually, Isaac wasn't hit on the head by a falling apple— that's a myth. But over time, he observed that objects always fell down toward the ground. These observations, combined with his curiosity, drove him to study gravity. Sir Isaac Newton (1642-1727) Isaac Newton was born on Christmas Day in Woolsthorpe, England. He lived on a farm with his grandmother. He had little interest in becoming a farmer and chose instead to study math and science at Trinity College, which is part of the University of Cambridge in England. At age 27, Newton conducted experiments with light and was the first to suggest that light was actually made up of all the colors. He eventually became one of the most famous scientists of all time!

Newton's First Law of Motion Isaac Newton is best known for writing three laws of motion that explain how all things move. The first part of Newton's first law says that an object at rest will remain at rest unless a force acts upon it. For example, your bike will stay parked where it is unless someone or something moves it. The second part of the first law states that an object in motion will continue in motion at the same speed and in the same direction unless a force acts upon it. So if your bike is rolling, it will continue moving just as it is until you pedal faster, coast, brake, or turn. If a force, such as a headwind, pushes from the opposite direction of the bike's motion, it will slow the bike or stop it completely. If a force, such as side wind, is applied to one side of the moving bike, the bike will change direction. Word Wise The word law often means a rule made by a government that people must obey. In science, a law is a statement about results that always occur under certain circumstances.