# Physics 6 Friction

Rub your hands together. Do your hands get warm? Why do they get warm?

Two surfaces like your two hands catch at each other when they are rubbed together. It’s called friction.

Question: How does friction affect gravity?

Materials:

Room with carpet

Ball ramp

Light and heavy balls

Wooden ramp

Meter stick

Jar with lid

Water

Procedure:

Prop up the ball ramp 0.5 m

Roll the light ball down the ramp several times

Note: If the ball rolls farther than the room wall, start the ball lower down on the ramp. Both balls must start at the same place on the ramp.

Roll the heavy ball down the ramp several times

Roll the light ball down the ramp and mark where it stops

Roll the heavy ball down the ramp and mark where it stops

The red ball is lighter than the rubber ball. The heavier ball rolls farther before it stops.

Measure how far apart the two places are

Prop up one end of the wooden ramp 0.5 m

Roll the empty jar down the ramp several times

Even started half way down the ramp the jar is rolling very fast when it gets to the floor.

Note: Start lower down on the ramp if the jar rolls too far across the floor and hits the wall. The empty, half full and full jars must start at the same point on the ramp.

Roll the empty jar down the ramp and mark where it stops

Fill the jar half full with water and put the lid on tightly

Predict whether the jar will roll farther, the same distance or a shorter distance

Roll the jar in your hands and see what the water does inside the jar

Gravity pulls the water to the bottom of the jar and keeps it there even when the jar is rolled in the hands or the jar rolls down the ramp.

Roll the jar down the ramp several times

Roll the half full jar down the ramp and mark where it stops

Fill the jar with water and put the lid on tightly

Predict whether the jar will roll farther, the same distance or a shorter distance

Roll the jar in your hands and see what the water does

Roll the jar down the ramp several times

Roll the full jar down the ramp and mark where it stops

Compare where the empty, half full and full jars stopped

Observations:

Which ball rolled the farthest

How much farther this ball rolled

Describe what the water does when you roll the half full jar in your hands

Describe what the water does in the full jar when you roll it in your hands

Predictions:

How far the full jar will roll

How far the half full jar will roll

How far will this jar roll before stopping? Does putting water in the jar change how far it will roll?

What happened:

Which jar rolled the farthest

Which jar was in the middle

Which jar rolled the shortest distance

Conclusions:

Draw a ball rolling on the carpet. Add the vector arrows to show the forces acting on it

In the last Project we found that gravity pulls the same on a light and a heavy ball. Does friction act the same on a light and a heavy ball? Why do you think so?

Does your carpet have a lot of friction? Why do you think so?

When your jar rolled in your hands, did the water roll with it? Why do you think so?

Draw the empty jar on the carpet and the vector arrows showing the forces acting on it

Does this drawing look a lot like the one of the ball?

Draw the half empty jar on the carpet and the vector arrows showing the forces acting on it

Is there another force arrow on this drawing? [Remember what the water is doing.]

If the half full and full jars were just that much heavier than the empty jar, do you think they would roll farther?

How does the water change how far the jars roll even though the water adds weight?

The ball on the left marks where the half full jar stopped. The next ball is where the full jar stopped. The ball on the right, much further than the others, marks where the empty jar stopped.

What I found Out

I set my ball ramp up and rolled the light ball down from the top. It raced across the carpet and hit the far wall. I had to release the ball about half way down the ramp for it to stop on the carpet.

The heavy ball raced across the carpet a little over a meter farther than the light ball. Since both balls ran over the same piece of carpet, the friction on the balls would be the same. However the heavy ball rolled a meter further so friction took longer to stop the heavy ball than the light ball. Friction is affected by weight.

The carpet is indoor outdoor carpet with short tight stiff loops packed close together. It doesn’t seem to have a lot of frictional force as the balls roll easily across it.

The first time I released the jar from the top of the ramp, it rolled across the carpet and hit the wall. I had to release it about half way down the ramp just as I did the balls. I marked where it stopped with a ball against the wall so the other jars would not hit my marker and move it.

When I rolled the half full jar in my hands, the jar turned easily. The water stayed level with the floor unless I turned the jar very fast so the water couldn’t run off the jar sides fast enough. The water moved opposite to the way the jar was moving.

Heavier things roll further than lighter ones so the half full jar will roll further than the empty one. At least that is what I thought would happen.

The half full jar stopped long before the empty jar had. The water was pushing to stop the jar from turning along with friction from the carpet.

When I rolled the full jar in my hands, there were a couple of bubbles in it so I could see the water was acting the same as in the half full jar.

After seeing that the water’s friction slowed the half full jar, I thought the full jar would not roll as far as the empty jar even though it had more weight.

When I released the full jar, it did roll farther than the half full jar. This must be because it weighed more. It did not roll as far as the empty jar so the water slowed it down.

If the three jars had just had different weights, the heaviest jar would roll the farthest and the lightest one the shortest distance like the light and heavy balls.