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# Friction

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by

## Emily Holdsworth

on 8 November 2016

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#### Transcript of Friction

"A force that opposes motion"
Friction
Friction
Friction is a force that opposes motion between two surfaces that are touching.
Force and Friction
The amount of friction between two surfaces depends on many factors. Some of them are:

1 -The surface of the objects. (Roughness or smoothness)

2 -The weight of the object.

Types of Friction
Static Friction
Sliding Friction
Rolling Friction
Fluid Friction

Sliding Friction
Sliding Friction = opposes motion of surfaces sliding past each other.
Rolling Friction
The force opposing rolling motion on a surface is called the rolling resistance or rolling friction.
Fluid Friction
Fluid friction is the force that resists the movement of a solid object through a fluid (liquid or gas).
Static Friction
When a force is applied to an object does not cause the object to move, static friction occurs.
Applying Friction
Arnold Schwarzenegger is moving out of his California mansion. He pushes a box of books on the floor with a force of 50 N to the right. The frictional force of the floor
opposes his push with a force of 30 N.
Friction occurs because the surface of any object is rough. Even surfaces that look or feel very smooth are actually covered with microscopic hills and valleys.
phet
You use sliding friction when you go sledding, when you apply the brakes on a bike, or when you write with a piece of chalk.
Another example?
Do you think sliding friction or rolling friction is greater? Explain.
Sky divers falling down through the sky experience a type of fluid friction called air resistance
The object does not move because the force of static friction balances the force applied.
Static Friction disappears when the object starts moving.
-Draw in the forces
-Are the forces balanced?
-Will the box accelerate? Which direction?
The forces are not balanced.
The box did accelerate because Arnold's force was stronger by 20 N.
Lubricants
Lubricants are substances that are applied to surfaces to reduce the friction between them.
Some examples are motor oil, wax, and grease.
Why do you think weight has anything to do with friction?
Weight and Friction
The force of friction is created when two bodies come in contact with each other.
If an object has a greater weight and is dragged on the floor, greater force of friction will be produced.
More weight, more contact force is created between 2 objects.
Forces and Motion: Basic
Static Friction
Static Friction= Prevents surfaces from sliding past each other. (No movement)
Static friction occurs when the force of friction is greater than the applied force.

When you push against a large object that is sitting on the floor and it does not move; static friction is keeping it from moving.

Finish the sentence
: Static friction
balances
the applied force. Static friction is only present
before
movement occurs.
Relationship between static friction and sliding friction...

When you push against an object on the floor, at first it will not move due to static friction. Once you apply enough force, the object
will begin to move.
You must keep applying a certain amount of force to overcome the sliding friction and keep the object moving.
VS
Finish the sentence
:
When a solid object moves through water or air, it slows down due to fluid friction. Fluid friction due to air is called
air resistance.
The amount of fluid friction depends upon the
object's shape
and
surface area
pushing against the fluid.
Full transcript