Newton's First Law and 3 States of Motion

 Question

So now that we know that both force and mass affect the motion of objects, in what ways do they affect an object's motion? Can you identify what those affects are and how we can observe them?

Objective

There are 3 states of motion that are address by Newton's first law of motion. Here we will go over each of those types of motion. At the end of this lesson you will be able to list the three states of motion that are affected by Newton’s first law of motion and explain how those three states of motion are affected using a ball or cup of water.  

3 States of Motion

1). An object is at rest and we attempt to move it.

2). An object is in motion and we attempt to speed it up or slow it down.

3). An object is in motion and we attempt to change its direction.

Let's look at an example of these in action by considering why your coffee might spill while you are driving.

Suppose you are in a car and you have a cup of coffee in the cup holder. If you were to take the lid of the cup off you will notice that as you accelerate the coffee moves towards the back of the car. This is similar to the standing in a bus example we went over earlier.

Figure 6

If while driving you suddenly step on the gas or slam on the brakes, what do you think would happen to the coffee? How would the coffee's motion change?

Of course the coffee would spill, tilting backwards when you accelerate and tilting forwards when you break. This is due to the coffee wanting to resist changes in it motion. When you break the coffee wants to keep moving forward at the same speed the car was moving at previously, however when it does so it goes over the rim of the cup and spills over.

Figure 7

Now suppose you come to a curve in the road and keep traveling at the same speed. What happens to the coffee?

You will notice that when you turn the coffee will begin to lean away from the turn. This is because if want to keep moving straight ahead and thus it might spill as it attempts to do so.

Example Problems

1). Suppose you have a ball rolling on a road. Can you identify what happens to the ball if you leave it alone? What about if you start to push the ball, what will happen? Finally suppose the ball comes to a curve on the road, what do you think will happen? Why would this happen?

2). Match the following events with the type of motion that is occurring.

A). Rolling across the back seat of a car as it makes a quick turn.

B). Lunging forward in a car as someone slams on the breaks.

C). A ball starting to move as we apply a force to it.

Once you have had a chance to think about these problems you may view the tutorial below, which goes over the solutions.

These ideas we have discussed have help us to develop Newton's First law of motion, which states:

Every object continues in a state of rest or of uniform velocity in a straight line unless acted upon by a non-zero net force.

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