Again, the first law of motion states that an object at rest will remain at rest, and an object that is moving at a constant velocity will continue moving at a constant velocity unless acted upon by unbalanced force.

The first law has two parts. Let's break it down and look at each part.

### Part 1: Objects at Rest

An object at rest is an object that is not moving. Objects are at rest all around you. Look around the room. What objects do you see that are at rest?

Source: Dominoes Falling, For Sound Money

The first law of motion states that this object will stay at rest until it is acted upon by an unbalanced force. In other words, an object will not start moving until a push or pull is exerted on it.

Watch the following video. What was the force acting upon the dominos?

Source: Guinness World Record-Longest/Biggest Domino Line Ever, Shanesdominoez,YouTube

The dominoes were at rest until an unbalanced force acted upon the first domino. What was the unbalanced force?

Interactive popup. Assistance may be required.

Someone pushed the first domino.

What was the force that acted up each of the rest of the dominoes?

Interactive popup. Assistance may be required.

Each domino was pushed down when the domino before it fell.

### Part 2: An Object In Motion

The second part of the first law of motion states that once an object is moving, it will stay moving until it is acted upon by an unbalanced force.

Look at the images below. If the blue car is sitting still (at rest), what will happen to it if the purple car hits it head on? Will the car move? If so, in what direction will it move? What will happen to the purple car after the two cars collide? Click on the purple car to see what happens.

Sources of images used for the interactive in this section:

• Bumper Car 5, GigiRocks, Clip Art Mojo
• Bumper Car 2, CaryGary, Clip Art Mojo