ShareForce, Energy, & Motion - Changing Force and Motion
Isaac Newton (a 17th century scientist) explained three laws that we still use in science today. These three laws explain why objects move (or don't move) as they do. In the years that followed, these three laws have become known as Newton's three laws of motion. These three laws are important principals that engineers use to design objects and machines. In addition, the principles of these laws help in determining how to change forces or motion.
Perhaps the most important concept to understand is Newton's first law of motion. This law becomes very important in the engineering of many products. As you continue on this page, try to determine how Newton's first law of motion applies in your life.
Newton's first law of motion is often stated as:
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. If the forces acting on an object are balanced, you can describe the motion (or lack of motion) of an object as follows:
You can demonstrate Newton's law by doing the following activity!
Materials:
- Plastic bucket
- Water
- Several friends
- Outdoor location
Procedure:
- Fill the bucket to the top with water.
- Get your friends to make relay group outdoors.
- Make sure that your group can move the bucket of water in a complete circle.
- Your goal will be to get the water to from one person to another around the circle.
- Run with the bucket to the next person in the relay!
- If you are the last person in the relay, stop as quick as you can when you get back to the starting person.
Safety concerns: 
Be sure to follow all chemical safety rules that are specified by your teacher in all general laboratory
experiences. As with all science lab activities, the most important safety
rule is to follow all teacher directions.
Analysis:
- At which locations in your relay did the water have a tendency to spill?
- At which points did you notice that the water did not seem to try to spill out?
Newton's first law of motion can explain the behavior of the water during the relay race. The water spills whenever the state of motion of the container changes. The water resists this change in its own state of motion and tends to "keep on doing what it is doing." If the container is moved from rest to a high speed at the starting line; the water remains at rest and spills onto the table. When the container stops near the finish line; the water keeps moving and spills over the container's leading edge. If the container is forced to move in a different direction to make it around a curve, the water keeps moving in the original direction and spills over its edge.
Balanced vs. Unbalanced Forces
When you study Newton's first law, you'll run into the phrase, "balanced
and unbalanced forces" quite often. If forces are balanced, what
does that really mean? To understand better, look at an object on a
table. What are the forces acting on it? There is gravity pulling the
object down and the table is pushing the object up. The object is not
moving anywhere - its state of motion remains the same because the forces
equal each other but point in opposite directions. If you could suddenly
pull the table out from under the object, there would be no force to
balance the force of gravity (forces become unbalanced) and the object
would fall (move in the direction of the force of gravity).
Analysis:
- If the forces acting on an object are balanced, must the object remain stationary?
- How can unbalanced forces acting on a car change the car's motion when the steering wheel is turned?
