Newton’s laws of motion describe the relationship between the forces acting on a body and the motion of the body.
Newton’s First Law of Motion: This law describes inertia, which means a body will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced net force.
Example of the inertia of an object at rest: You can remove a paper from beneath a standing clothes pin and the pin will fall into the container beneath it.
Discover for Yourself:Place an index card over the mouth of a heavy drinking glass or jar. Stand a clothespin on top of the card so that it is centered over the glass. Quickly and forcefully thump the card straight forward with your finger. You want only to hit the card and you want the card to move in a horizontal direction.
Results: The clothespin falls straight into the glass about half of the time; the other half of the time it flips over landing upside down in the glass.
Why? Your finger applies force to the card, moving it forward. The card quickly moves out from under the clothespin and the pin falls straight down due to the pull of gravity. If you do not hit the card straight forward and/or it is not hit with enough force, the cards pulls the bottom of the pin forward and gravity pulls the top of the [pin down, causing the pin to flip before it lands.
For more information about inertia, see NEWTON’S FIRST LAW OF MOTION: INERTIA