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Newton's First Law of Motion
You may already by familiar with Newton's First Law of Motion. This law is often stated: Objects in motion tend to remain in motion (at a constant velocity) unless acted upon by an unbalanced force. This is also true for objects at rest. Objects at rest tend to stay at rest unless acted upon by an unbalanced force.
Basically, to summarize this law, objects will continue to do whatever they are doing (moving or being at rest) until an unbalanced force acts on them.
Think about the example we have been using of the book on the desk. It is going to stay sitting on the desk until some type of unbalanced force acts on it. Now, what about when you give that book a push, and it slides across the desk? Newton's First Law says that it should keep sliding until acted upon by a force. Well, we know that the force acting upon it is friction, which eventually brings the book to a stop.
Take a look at the following example:
- In diagram A, the rocket is sitting on the launch pad. The weight (force of gravity) of the rocket is exactly opposed by the upward force (the normal force) from the launch pad. These forces oppose each other and result in a zero net force. Since no other force acts on the rocket, it will remain at rest.
- In diagram B, the rocket thrusters exert a force, which overcomes the weight of the rocket. The net force is no longer balanced and the rocket begins to move upward.
Now, watch the following videos for an overview of Newton’s first law.