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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