2Friction DefinitionFriction occurs when 2 objects are in contact with each other. The objects apply or exert a force on one another during this time.Friction acts in the opposite direction of motion – so it is the force that resists movement!share.ehs.uen.org
3Factors that Affect Friction How hard the surfaces push against each other – the more force, the higher the frictionThe type of surfaces involved – the smoother the surface, the lower the friction
4Friction and Smooth Surfaces Even apparently smooth surfaces actually have microscopic irregularities and bumps. When these come in contact with another surface friction occurs.
5Direction of FrictionFriction acts in the opposite direction of motion, so if the object moves towards the right the frictional force will be towards the left.
6Static Friction Definition: The friction that occurs when objects are not moving. It is the friction that keeps objects in place.Example:A box sitting on the ground, your books sitting on a table, your backside against the chair.
7How to “Overcome” Static Friction The force needed to start an object moving must be greater than the static friction.Reason why a greater force is needed to start an object moving than to continue it movingeducation-portal.com
8Sliding Friction Definition: The friction that occurs when 2 solid objects move against each other (or 1 object moves over another)Example:Bicycle brakes, skinning your knee, walking, writing
9Usefulness of Sliding Friction It can keep you from slipping, sliding and falling (example: sand on an icy road)!
10Rolling Friction Definition: The friction that occurs when an object rolls across a surface.Easier to overcome than sliding friction.Example:Anything with wheels (cars, skateboards) or a ball rolling.
11Rolling Friction and Engineers Engineers use ball bearings to reduce friction – the ball bearings roll between moving parts.news.thomasnet.com
12Fluid Friction Definition: The friction that occurs when a solid objects moves through a fluid. A fluid is a gas or liquid – they flow easily!Easier to overcome than sliding friction.Example:Anything moving through the air or water: riding a bike, surfing, swimming, sky diving
13Usefulness of Fluid Friction Parts of machines move more easily when they are oiled.Fluid friction is what slows down a skydiver when the parachute is opened.