FRICTIONFRICTION

A force that A force that opposes opposes motionmotion

Objectives…Objectives…

Explain why friction occurs.Explain why friction occurs. List the two types of friction, and List the two types of friction, and

give examples of each type.give examples of each type. Explain how friction can be both Explain how friction can be both

harmful and helpful.harmful and helpful.

What is friction?What is friction?

Is a force that Is a force that opposes motion opposes motion between two between two surfaces that are in surfaces that are in contactcontact

When does friction occur?When does friction occur?

Friction Friction occurs occurs when two when two surfaces surfaces are in are in contactcontact

Also…Also…

When a When a liquid or liquid or gas is gas is pushed out pushed out of the way of the way of a of a moving moving objectobject

Why does friction Why does friction occur?occur?

Because the hills and valleys of a Because the hills and valleys of a surface are in contact with the surface are in contact with the hills and valleys of other hills and valleys of other surfaces, this produce friction.surfaces, this produce friction.

Friction depends Friction depends on…on…

Roughness of surfaces Roughness of surfaces and and

Force that objects are Force that objects are being pressed one being pressed one against the other; or against the other; or their weightstheir weights

What increases What increases friction?friction?

Rough surfacesRough surfacesAnd weight of objectsAnd weight of objects

What does the amount of What does the amount of surfaces depend on?surfaces depend on?

the amount of friction depends the amount of friction depends on how well the surfaces grip on how well the surfaces grip each other.each other.Tyres on a on a road have very have very high frictionhigh friction (they don't slip),(they don't slip),skatesskates on on iceice have very have very low low frictionfriction (they slip easily).(they slip easily).

In a liquid or a gasIn a liquid or a gas

For a solid object moving For a solid object moving through a liquid or gas,through a liquid or gas,the amount of friction depends the amount of friction depends on the shape and surface area on the shape and surface area of the objectof the objectand the viscosity (thickness or and the viscosity (thickness or thinness) of the liquid.thinness) of the liquid.

TYPES OF FRICTIONTYPES OF FRICTION

KINETIC ANDKINETIC ANDSTATICSTATIC

What is kinetic What is kinetic friction?friction?

Is the friction Is the friction between two between two moving surfacesmoving surfaces

Sliding and Sliding and RollingRolling

Static frictionStatic friction It occurs when a force It occurs when a force is applied to an object is applied to an object but this object but this object doesn’t move.doesn’t move.

Static frictionStatic friction

Is friction good or bad?Is friction good or bad?

Friction can be good.Friction can be good.When we walk we push When we walk we push backwards against the backwards against the ground,ground,the the opposing force pushes us forwards.pushes us forwards.Without frictionWithout friction our feet our feet would slip and would slip and walking walking would be impossible.would be impossible.

It is also goodIt is also good

To stop To stop your your bicycle bicycle (brake (brake system)system)

But sometimes is bad…But sometimes is bad…

Soil erosion caused by wind Soil erosion caused by wind (friction of a fluid).(friction of a fluid).

Holes in your shoes, jeans. Holes in your shoes, jeans. (friction of a solid) high friction(friction of a solid) high friction

Lack of friction is dangerous too, Lack of friction is dangerous too, you may fall if the floor is very you may fall if the floor is very slippy.slippy.

Some ways to reduce Some ways to reduce frictionfriction

Some ways to increase Some ways to increase frictionfriction

GO TO THIS LINK TO INCREASE YOUR GO TO THIS LINK TO INCREASE YOUR KNOWLEDGE ABOUT FRICTIONKNOWLEDGE ABOUT FRICTION

http://www.gcsescience.com/http://www.gcsescience.com/pfm32.htmpfm32.htm