FrictionLesson 11

Have you ever wondered why ice is so slippery to walk on?

Have you ever wondered why it is harder to push a wheel barrow on rocks or grass than on a road or

sidewalk?

These effects are caused by friction.

What is friction?

Friction: a force that opposes the motion of any object moving on it.

Friction is a type of force that is caused when two surfaces rub

together.

What happens when you rub your hands together?

Did you feel your hands warm up? That heat you felt was created by the friction you were making by rubbing your hands together!

There are many things we could not do with out friction.

You could not walk without the friction between your shoes and the ground. As you try to step forward, you push your foot backward.

Friction holds your shoe to the ground, allowing you to walk. Consider how difficult it is to walk on slippery ice, where there is little friction.

Writing with a pencil requires friction. You could not hold a pencil

in your hand without friction. It would slip out when you tried to hold

it to write.

The graphite pencil led would not make

a mark on the paper without

friction.

.

.

A pencil eraser uses friction to rub off mistakes written in pencil lead. Rubbing the eraser on the lead wears out the eraser due to friction, while the particles worn off gather up the pencil lead from the paper!

Your car would not start moving if it wasn't for the friction of the tires

against the street. With no friction, the tires would just spin.

Likewise, you could not stop without the friction of the brakes and the

tires.

Friction changes how a force moves an object.

Take your pencil and roll it on a smooth surface like a smooth table.

How did it roll? Did it roll far?

A smooth table top has very little friction so the pencil can roll a long

way.

You can lay a shirt or a sweater on the table and then try to roll your

pencil on the sweater or shirt. How does your pencil roll now?

The pencil did not roll as far as it rolled on the table.

The shirt is causing a lot of friction.

Friction causes motion to slow down. The shirt or sweater caused the pencil

not to roll as easily as it did on the table.

Try rolling your pencil on the ground or on the grass. How does

it roll?

The grass or dirt is a form of friction. So the pencil would not be able to

roll as smoothly as it did on the table.

Break Time

Let’s look at some more examples of friction.

http://www.bbc.co.uk/schools/scienceclips/ages/8_9/friction_fs.shtml

What would happen if friction did not exist?

Things would not stop moving. We need friction.

Now let’s experiment with friction.

Please have handy your objects and your Friction worksheet.

Watch the video to see how I did the experiment.

http://www.youtube.com/watch?v=aE7iZdJAkJQ

Penny on table

Penny on shirt

Penny on grass

http://www.youtube.com/watch?v=dr51ckYHqaI

http://www.youtube.com/watch?v=3xWt1wOY5Pw

Today we learned that friction is important and

without it we would not be able to walk,

write and stop objects.

In our next lesson we will learn about resisting forces.

Keep observing the world around you!