Much of what we know about the world today is built upon the work of Sir Isaac Newton, a scientist who lived in the 17th and 18th centuries. He built upon the earlier work of Galileo to develop laws for how motion works in the world. He summarized his work in three laws.
<span>First Law: A moving object tends to keep moving at the same speed and in the same direction unless a force acts on it. An object at rest tends to stay at rest unless a force acts on it.</span>
What does this mean?
It's pretty obvious that a stopped object doesn't move unless someone moves it. The second sentence, however, is harder to believe. It says that objects in motion tend to stay in motion unless stopped by a force. Said another way, until someone or something makes an effort to stop them, they'll keep moving. This tendency of an object to keep moving is called inertia. This is sometimes hard to see in the real world. When you throw a ball, it's going to stop when it hits the ground, even if it rolls for a while. This is because the air that the ball moves through pushes back on it and exerts a force. This pushing back is called friction. The ground also exerts a frictional force as the surface of the ball rubs against the surface of the ground. Without friction a thrown ball would roll forever.
How can I test it?
It's easy to test the first part. Set a ball in a stable position. It doesn't move. If you set it on a hill, it will roll down. That's because gravity exerts a downward force on it.
<span>Now let's build something to test the second part.</span>
