# Physics 5 Exploring Friction

Rub your hands past each other once. What do you feel?

My hands feel rough against each other. I can feel friction between them.

Now rub your hands back and forth a dozen times or so. What happens?

My hands warm up. I use this when my hands get cold in the winter.

Friction makes the heat. It does other things too.

Question: How does friction work?

Materials:

Smooth block of wood like a couple of inches of a 2 x 4

2 Pieces of Sandpaper

Tape

Smooth board about 0.5 m long

Meter stick

Procedure:

Rub the block of wood on your hand

Describe how it feels

Rub the piece of sandpaper on your hand

Describe how it feels

Push the block of wood down the smooth board

Describe how it feels

Set the block of wood on one end of the board

Lift that end of the board until the block slides down the board

It didn’t take long for the block to slide down the varnished board. The two smooth surfaces had little friction between them.

Measure how high you lifted the board

Tape the sandpaper rough side out on the block

The sandpaper on the block felt very rough especially compared to the smooth sanded block surface.

Push the block on the board

Describe how it feels

Set the block on one end of the board

Lift that end of the board until the block slides down the board

Measure how high you lifted the board

Tape a piece of sandpaper on the long board

I had a long piece of sandpaper used on a belt sander so it covered the length of the board.

Push the block on the long board

Describe how it feels

How high do you think you will have to lift the board this time?

Set the block on one end of the board

Lift the end of the board until the block slides down the board

Measure how high you lifted the board

Observations:

Describe how the block feels against your hand

Describe how the sandpaper feels against your hand

Describe pushing the block on the board

Describe pushing the block with sandpaper on it down the board

Describe pushing the block with sandpaper down the board with sandpaper

How high do you think you will lift the board the last time?

Measurements:

Plain block on plain board

Block with sandpaper on plain board

Block with sandpaper on board with sandpaper

Even the varnished board was rough enough for the sandpaper to hold to and keep the block from sliding down.

Conclusions:

Does the block or the sandpaper have more friction? Why do you think so?

Which of the three times you lifted the board was there the most friction? Why do you think this?

What did increasing the friction between the block and board do?

How could you decrease the friction between the block and board?

How could you increase the friction between the block and board?

Car tires use friction to keep and move the car on the road. What creates this friction?

Why is it important to not have smooth tires?

Why is driving on ice so dangerous?

The block seemed stuck to the board as I raised the board higher and higher. Shortly after taking this picture, the block tumbled down the board.

What I Found Out:

My block was a piece of a two by four so it was sanded smooth and felt smooth against my hand. The board was varnished on one side and that side felt slick. Rubbing them against my hand made my hand a little warm.

I put the block on the varnished side of the board and lifted the end. The end was 17.3 cm high when the block slid down.

The sandpaper was rough on my hand and made my hand hot rubbing it. I put the block on the varnished side of the board and started lifting that end. It was 30.5 cm high before the block slid down.

When the block with sandpaper on it was set on the board with sandpaper on it, I had to lift the end up 35.5 cm and the block tumbled off instead of sliding.

The block had a lot less friction than the sandpaper because it felt smooth and only warmed my hand up rubbing it. The sandpaper scraped my hand and made it feel hot.

Friction makes it harder for an object to move so the third time with sandpaper on both the block and the board had the most friction. I had to raise the board really high to get the block to move and then it fell off.

The smooth block and board had  the least friction so any way to make them smoother would decrease the friction even more. Using rougher sandpaper on both the block and board would increase the friction.

A car tire has treads. Roads are usually rough. Rougher kinds of tread and rougher roads would increase the friction. Smooth tires would have a lot less friction letting the tires slide on the road.

Ice is really smooth and slick. It would reduce the friction a lot so the tires would slide.