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:
A magician’s trick of pulling a table cloth out from under a table setting and leaving the dishes standing can be explained by inertia. You can do a simplified version by knocking a paper loop from beneath a coin. Do this using a 1-by-24-inch (1.25-by-600-cm) strip of poster board. Secure the ends of the paper with tape to form a loop. Set the loop on a quart (1 liter) jar. Place a penny on top of the loop directly above the center of the jar’s mouth. Sweep the end of the pencil past one side of the loop and strike the inside of the opposite side so that the pencil carries the loop away and the coin drops in the jar. You may need to practice a few times before performing this trick for friends.
Results: If hit properly, the coin falls straight into the glass. If hit improperly, the coin falls outside the jar.
Why? Your pencil applies force to the loop, moving it forward. The loop quickly moves out from under the coin and the coin falls straight down due to the pull of gravity. If you do not hit the loop straight forward and/or you do not hit the look with enough force, the loop pulls in the bottom of the coin forward. If the forward motion of the coin carries the coin past the jar’s opening, the coin will fall outside the jar.
Example of an object in motion: A thrown ball.
If you throw a ball, the ball would continue to move at a constant velocity unless a force acts on it. Since things do not continue to move, we know that some force stops them, this force is gravity. A thrown ball moves upward for a time, but then falls to the ground. It falls in the direction the the force of gravity pulls it, which is down.
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