A force that opposes motion between two surfaces that are in contact Causes a moving object such as a ball to slow down and stop Occurs because the surface of any object is rough microscopic hills and valleys ID: 551698
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Slide1
What is Friction?/Lesson 6
A force that opposes motion between two surfaces that are in contact.
Causes a moving object, such as a ball, to slow down and stop.Occurs because the surface of any object is rough (microscopic hills and valleys)Slide2
Source of Friction
When two surfaces are in contact, the hills and valleys of one surface stick to the hills and valleys of the other surface.
The amount of friction between two surfaces depends on: the force pushing the surfaces together Increase in force = increase in frictionHeavier weight = increase in frictionthe roughness of the surfaces.
Rougher surface=more hills and valleys=increase in frictionSlide3
Types of Friction
Kinetic “moving”
Friction between moving objectsSlidingApplying the brakes of a bicycleRollingAnything that has wheelsStatic “not moving”
When a force is applied to an object but does not cause it to move
Overcome by applying a large amount of forceSlide4
Friction: Harmful or Helpful
Helpful
Car tires to ground = moving carCar brakes to wheels = stopped carPencil to paper = leaves a mark (your handwriting)Keeps you from slipping and falling when walking
Harmful
Increased temperature in car parts can wear the parts down
Holes in your socks
Wind and water eroding topsoil that nourishes plantsSlide5
Reducing Friction
Lubricants applied to surfaces to reduce friction
Examples: motor oil, wax, and grease.Changing the type of frictionSliding kinetic friction to rolling kinetic frictionExample: ball bearings in in-line skates and bicyclesMake surfaces that rub against each other smoother.Rubbing the surfaces with sandpaperSlide6
Increasing Friction
Make surfaces rougher
Examples: sand scattered on icy roads, baseball players wearing textured batting glovesIncrease the force pushing the surfaces togetherExample: pressing sandpaper harder when sanding a piece of wood.