Physics 5 Gravity and Galileo

Even though Sir Isaac Newton is famous for his Laws of Motion, Galileo studied how gravity affected motion long before Newton did. He didn’t have a good clock or watch with a second hand or any idea about a stopwatch. He used his pulse or a water clock that has a bowl of water with a tiny hole so the water drips out at a steady rate.

Galileo did the best he could with the equipment he had and did write down laws of motion very similar to those later written down by Newton. He was the first scientist to test some ideas people had believed for years and never thought to test.

Like Galileo we will be using the force of gravity for several Projects. We have used it for the Projects we’ve already done. So we will take a closer look at gravity and some ways it works and things that affect it.

This Project works much better with two people doing it.

Question: What are two things Galileo discovered about gravity?

Materials:

2 balls alike in substance, size and weight

2 balls alike in size [Use solid balls] but different in weight [at least double]

Grooved ramp at least a meter long

Procedure:

Look over the two balls alike in size but different in weight

Mass the two balls

You will drop the two balls from the same height at the same time

Predict which option will be true and why you think so:

1) The heavy ball will fall faster

2) Both balls will fall at the same speed

3) The lighter ball will fall faster

One person drop the balls from the same height at the same time while the other person watches to see which option is true.

Dropping two balls at the same time is harder than it sounds. Using one hand to hold and release both balls worked the best for me.

Try dropping the balls from different heights

Like Galileo we will be timing how fast a ball or car moves when pulled by gravity

Look over the two balls alike in size, substance and weight

When you use a stopwatch, you click it on when the ball or car begins to move and click it off when a certain distance is covered.

Drop one of the balls from a meter high

Could you click a stopwatch on and off in that time?

Set up the grooved ramp so one end is one meter high

I got a large piece of cardboard and folded it double to make a stiff ramp. It had to be taped to keep the folded parts together.

One ball will run down the ramp while the other drops the same height to the floor

Predict which option will be true and why you think so:

1) The ball dropping straight to the floor will drop fastest

2) Both balls will fall to the floor at the same time

3) The ball going down the ramp will get to the floor first

One person holds a ball at the end of the ramp and one over the floor at the same height

That person lets the balls go at the same time while the other person watches to see which option is true

Observations:

Describe the two balls:

Mass of Ball 1:

Mass of Ball 2:

Write down your prediction and reason for choosing it

Describe what happens when the two balls are dropped:

A heavy and a light ball fall together. Gravity pulls on both the same.

Explain why you can or can’t use a stopwatch to time how fast the ball drops:

Describe the two balls:

Write down your prediction and reason for choosing it

Describe what happens when one ball drops straight down and the other goes down a ramp:

Conclusions:

What forces are acting on the two balls as they fall when you drop them?

Which force is the most important? Why do you think this?

Does mass seem to matter to this force? Why do you think so?

What forces are acting on the two balls, one dropped and one on the ramp?

The ball going straight down got to the floor long before the ball rolling down the cardboard ramp even though gravity was the force pulling on both.

Which force seems to matter the most? Why do you think so?

Does distance traveled seem to matter to this force? Why do you think so?

What do you think would happen if the ramp were more level? Try it and find out.

Why do you think this is the case?

What do you think would happen if the ramp were steeper? Try it and find out.

Why do you think this is the case?

Do you think it is possible to use a stopwatch to time a ball going down a ramp? Why do you think this?

What I Found Out

I had to use a ping pong type of ball for my light ball and a rubber ball for the heavy one. It seems easy to think the heavier ball will fall faster because it is heavier. I can’t really predict this because I know what will happen.

When the balls dropped, both dropped straight to the floor. They hit the floor at almost the same time. I found I had to have both balls in one hand to be sure they dropped at the same time.

Gravity was pulling the balls down. Air was pushing up on the balls like it did the sheet of paper but the balls were too small and heavy for the air to push hard enough to slow them down.

Gravity doesn’t seem to care about mass as the balls hit the ground at the same time. It pulls the balls down very fast, faster than I could start and stop a stopwatch.

When I set up my ramp, I thought the two balls would hit the floor at the same time even though one ball had to travel much farther. Gravity was pulling the same on both so they should fall at the same speed.

Thinking it over now I can see the ball going down the ramp would have to get to the floor after the ball dropped straight to the ground. This is what happened. Changing the slope of the ramp made the ball take more time on lesser slopes and shorter times on steeper ramps.

Gravity does pull the same on the two balls but the distance does matter. Since a ball travels down a ramp more slowly than being dropped, I think I could time it with a stop watch.