- Force of friction: Acts in a direction opposite to the applied force.
- Nature of friction:
- Smooth surface less friction
- Rough surface more friction
- Surface offers friction because –
- Each surface objects have irregularities, which causes interlocking. If force is enough to overcome interlocking then object moves giving rise to friction, if not then object do not move.
- Friction also depends on the extent to which surfaces are pressed on each other. If objects are strongly pressed over each other, extent of interlocking is higher thus, friction has to higher.
- Types of friction:
- Static friction: Measure of force required to overcome friction at the instant an object starts moving from rest.
- Sliding friction: Force required to keep the object moving with the same speed
- Static friction > Sliding friction
- Rolling friction: Resistance to motion of body rolling over the other
- Rolling friction << Sliding friction
- Friction can be increased in the following cases:
- Grooves in soles of shoes and tyres of vehicles to increase friction
- Vehicles have brakes to increase friction so as to stop motion of vehicles
- Gymnasts rub their hands in soil or other rough surfaces to have a firm grip over the object they are holding
- Friction can be decreased in following cases:
- Sprinkling powder on carrom board reduced friction on the board
- Grease is applied in automobile parts to reduce the friction
- Oil is added in hinges of doors to smooth the motion of door
- Fluid friction: Opposes movement of object in fluid
- Drag: Frictional force exerted by fluid
- Factors affecting friction:
- Shape of object: To minimise fluid friction objects have special shapes like shape of aeroplane is similar to bird, shape of submarine is similar to fish, etc.
- Nature of fluid: More viscous fluid offer more resistance, less viscous fluid orffer less resistance.
- Viscosity: Property of fluid to offer resistance to the flow.
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