# AP Board 8th Class Physical Science Notes Chapter 2 Friction

Students can go through AP State Board 8th Class Physical Science Notes Chapter 2 Friction to understand and remember the concept easily.

## AP State Board Syllabus 8th Class Physical Science Notes Chapter 2 Friction

→ Friction opposes the relative motion between two surfaces in contact. It acts on both surfaces.

→ Friction depends on the nature of the surface in contact.

→ For a given pair of surfaces, friction depends upon the state of smoothness of those surfaces.

→ Friction depends on how hard the two surfaces pressed together which is a normal force acting on the body.

→ Friction is independent of the area of contact.

→ Static friction comes into play when we try to move an object at rest relative to another surface or object.

→ Sliding friction comes into play when an object is sliding over another.

→ Sliding friction is smaller than static friction.

→ Friction is important for many of our activities.

→ Friction can be increased by making a surface rough.

→ The sole of the shoes and the tires of the vehicles are threaded to increase friction.

→ Friction is sometimes undesirable.

→ Friction can be reduced by using lubricants.

→ Friction produces heat.

→ When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than sliding friction.

→ In many machines, friction is reduced by using ball bearings.

→ When bodies move through fluids, fluids exert a frictional force called drag.

→ Fluid friction can be minimized by giving a suitable shape to bodies moving in fluids.

→ Friction: The force which opposes the relative motion of two surfaces of bodies that are in contact.

→ Static friction: The friction which comes into play when surfaces of the objects are at rest relative to each other.

→ Sliding friction: Sliding friction is the friction that comes into play when the surface of one object moves relative to the surface of another object.

→ Lubricants: The substances which reduce friction are called lubricants.

→ Ball bearings: The devices which reduce friction between rotating shafts of machine tools.

→ Drag: The frictional force exerted by fluids is called drag.

→ Fluid friction: Pressure exerted by fluids is called fluid friction.

→ Rolling friction: When one body rolls over the surface of another body, the friction offered ¡s called rolling friction.

→ Fluids: Liquids and gases are called fluids.

→ Leonardo Davinci (1452-1519):

• Leonardo Davinci was one of the first scholars to study friction systematically.
• He realized how important friction is for the working of machines.
• He focussed on all kinds of friction and drew a distinction between sliding friction and rolling friction.