Chapter 5-2 The Foundations of Physical Science FORCES Chapter 5-2 The Foundations of Physical Science

FRICTION Friction is a force that resists motion Friction is found EVERYWHERE in our world Examples: You feel friction when you swim, ride in a car, walk, and even when you sit in a chair Friction can act when an object is moving or when it is at rest

Causes of Friction Two surfaces are involved Friction depends on both of the surfaces that are in contact Think of a hockey puck on ice or sandpaper --- there is a difference Water and other liquid, such as oil, can greatly reduce friction between surfaces

Direction of the Friction Force Friction is a force- like all forces-- it is measured in newtons Friction resists motion STATIC FRICTION- the friction force that resists the motion between two surfaces that are not moving

Identifying friction forces SLIDING FRICTION- the friction force that resists the motion of an object moving across a surface Example: pushing a box across the floor

Static Friction and Sliding Friction How do the two compare? It is harder to get something moving than it is to keep it moving Static friction is almost always greater than sliding friction at slow speeds

Reducing the Force of Friction Unless a force is constantly applied, friction will slow all motion to a stop eventually It is impossible to completely eliminate friction

Friction can be useful!!! Brakes They are on bikes, motorcycles, cars Cleated shoes Shoes are designed to increase friction between your foot and ground

FRICTION AND ENERGY Earlier we learned that energy moves through the action of forces Energy changes into different forms Friction changes energy of motion into heat energy You feel the EFFECT of friction changing energy of motion into heat