Chapter 10 Section 2

Friction

The force that two surfaces exert on each other when they rub against each other is called friction.

The Causes of Friction

◦The strength of the force of friction depends upon:

how hard the surfaces push together and the type of surfaces involved.(Smooth surfaces produce less friction)

Smooth surfaces produce less friction

◦Greater force produces more friction

Types of Friction

Static:The friction that acts on objects

that are not moving

Must use extra force to start the motion of stationary objects

Once object starts to move, there is no static friction

Sliding

Occurs when two solid surfaces slide over each other.

Can be useful, Sand on ice to gain traction, brakes

Can be harmful: Fall off bike and skin knee, heat produced

Rolling

When an object rolls across a surface

Easy to overcome

Example Ball bearings help reduce the friction between the wheels and the rest of the unit

Fluid Friction

Occurs when a solid object moves through a fluid

Easy to overcome

Fluids are used between 2 solid moving parts, the solids move through the fluid, not against each other

Occurs between you and the air when you ride a bike

Gravity

Gravity is a force that pulls objects toward each other.

Gravity is everywhere in the universe

Law of Universal Gravitation: the force of gravity acts between all objects in the universe

Factors that affecting Gravity

Mass: The amount of matter in an object

The more mass an object has, the greater its gravity

The Distance between the objectsThe greater the distance between the objects, the less gravitational force between them

Weight and Mass

◦Is the measure of the amount of gravitational force exerted on an object

Weight varies with the gravitational pull, mass does not