Lesson 3: Friction
Friction
 Is a FORCE that RESISTS THE MOVEMENT of one surface past another
surface.
 FRICTION occurs between TWO SURFACES RUBBING against each other.
It pushes in the OPPOSITE DIRECTION of an object’s motion causing the
object to SLOW DOWN OR STOP.
 SMOOTH surfaces produce LESS FRICTION
EXAMPLES: Gym Floor, Ice Rink
 ROUGH surfaces produce MORE FRICTION
EXAMPLES: Gravel road, Sandpaper, Carpet
**When an object slides over another, tiny rough places on both
surfaces produce a lot of friction.
Friction produces heat. If you rub your hands quickly together, you will
feel them get warmer.
Example of MORE friction being produced:
 The wind can produce friction, when it blows (rubs) against
objects. This can be called air resistance. When you are playing
soccer, you can run faster and kick the ball farther when it is less
windy (less friction). If it is a very windy day, the team who has
the wind blowing at them will have to work harder to kick the ball
because they have more friction – caused by the wind. The team
who is playing with the wind will be able to kick the ball farther
with less force being used, because the wind is helping them.
Ways to reduce friction:
 Adding oil or grease can control friction by filling in rough places
on surfaces.
 Adding wheels to an object. If you add wheels to a board, it will
move easier on the surface it is on and there will be less friction.
Examples of Ways to reduce friction –
 Adding wheels to a board: If you tried to push a board on grass
it would be difficult to move because too much friction is being
produced. If wheels were added to the board, the board would
move easier across the grass friction was reduced.
 Another way to reduce friction is to change the surface an object
is on. For example: If you are pushing a book on a carpet, it is
difficult to push. You would need to push the book hard (with a
lot force) in order to move it. You could reduce friction if you
moved the book to a wooden or a waxed floor. These surfaces
produce less friction and the book would move much easier.
 If you are playing on a slide, you will go down the slide faster is
you are wearing pants than if you are wearing shorts. Your skin
would rub against the slide and produce more friction. The
more friction you produce, the slower you will move down the
slide. Wearing pants allows les friction to be produced.
 When driving in a car, what causes friction to make the car stop?
The brakes rub against the wheels and create friction. The friction causes the car
to stop.
 What makes you stop in a car when it is moving?
Seatbelts overcome inertia by keeping you in the car when there is a sudden stop.
 How could we reduce friction on a soccer ball?
We could reduce the friction by making the surface smoother. We could cut the
grass. The shorter grass would reduce friction and the ball would roll faster and
further.
We could also exert more force on the ball by kicking it harder.
Add more air to the ball. This would allow the ball to roll faster.
 In the winter many people place chains on their tires. Why do
you think they do this? What are the effects?
The chains on the tires will increase (or add) friction to the tires. They will give
the tires a better grip to the road so the car does not slide.