# FRICTION

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### What is Friction?:

What is Friction? - Friction is the rubbing of one object or surface against another . Friction is force that appears whenever two things rub against each other . Although two objects might look smooth, microscopically, they're very rough and jagged .

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. If the object does not move, the friction is considered static . If the force is sufficient to move the object, the friction is called kinetic.

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There are 3 main types of friction : ( 1 ) sliding ( kinetic ) friction, ( 2 ) rolling friction, and ( 3 ) fluid friction ( viscosity ).

### PowerPoint Presentation:

1. Sliding friction is when two objects are rubbing against each other . 2. Rolling friction is the force that occurs when an object rolls. (e.g .: a wheel or tire ) 3. Fluid friction is the friction between a solid object as it moves through a liquid or a gas .

### PowerPoint Presentation:

Sliding friction When two solid objects are in contact and a force is applied to slide one object against the other, sliding friction force resists the motion. Causes of sliding friction The causes of sliding friction are surface roughness of the materials, molecular attraction or adhesion between the materials, and deformation resistance in the case of soft materials. Kinetic Friction If F is the force pushing on an object and Fr is the force of friction , the relationship between F and Fr will determine whether the object will slide or not move at all. Static friction If F is less than F r ( written as F < F r ), there is no motion and the objects remain static with respect to each other. In this case, the friction is considered static friction, which means it is not moving.

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Rolling friction When a ball or wheel is in contact with a solid object and a force is applied to the wheel, it will start to roll due to the friction at the point of contact with the other surface . This is the starting friction for a wheel . Causes of rolling friction They are surface roughness of the materials , molecular attraction or adhesion between the materials, and deformation resistance in the case of soft materials . Once the wheel starts rolling, there is a resistive force that slows the wheel's motion on the other surface . This is called rolling friction .

### PowerPoint Presentation:

Fluid friction When a solid object is in contact with a fluid, such as a liquid or gas, and a force is applied to either the object or the fluid, there is a friction force that resists the motion . Static and kinetic If the viscosity or thickness of the fluid is great, there may be no movement due to static friction . Causes of fluid friction are turbulence effects from surface roughness and deformities, molecular attraction or adhesion between the materials, and deformation resistance of the fluid .