NCERT Solutions Class 8th Science Chapter – 9 Friction Notes, Factors Affecting Friction, Friction is a must as well as evil, Friction can be reduced by using, Friction can be increased by making a surface rough
NCERT Solutions Class 8 Science Chapter – 9 Friction
Chapter – 9
Friction
Notes
Factors Affecting Friction
Friction depends on the nature of surfaces in contact.
For a given pair of surfaces, friction depends upon the state of smoothness or roughness of those surfaces.
It is less for smooth surfaces.
Friction is independent of the area of contact.
Friction depends on how hard the two surfaces pressed together.
Friction is a must as well as evil
Friction produces heat when we vigorously rub our palms together for a few minutes.
Friction is responsible for wear and tear of various parts of machines.
Friction decreases the efficiency of machines as a part of the machine’s energy is lost in extra friction.
Friction is responsible for writing, walking and transmitting energy.
Friction is responsible for starting or stopping.
Friction is used in gripping or holding an object with our hands.
So, we can say friction is a must as well as evil.
Friction can be reduced by using
grease, oil, powder, ball bearing, and cushion of dry air between the moving surfaces.
using anti-friction alloys.
Friction can be increased by making a surface rough.
The sole of the shoes and the tyres of the vehicle are treated to increase friction.
Fluid Friction can be minimised by giving suitable shapes to bodies moving in fluids.
To overcome fluid friction bodies of fish and birds are streamlined. Similarly, the ships and aeroplanes are also made streamlined.
Ball Bearing – Ball bearings reduce friction. They are used between hubs and the axles of ceiling fans and bicycles.
Drag – The frictional force exerted by fluids is also called drag.
Fluid Friction – Fluid exerts the force of friction on objects in motion through them.
Friction – Friction is the form of force, which opposes the relative motion between the two surfaces in contact and it acts on both the surfaces.
Interlocking – Irregularities on two surfaces in contact may clasp with each other, increasing friction.
Lubricants – The substances which reduce friction are called lubricants.
Rolling Friction – When one body rolls over the surface of another body, the resistance to its motion is called the rolling friction.
Sliding Friction – When one surface is sliding over the other surface, sliding friction comes into play.
Static Friction – Static friction comes into play to counterbalance the applied force on the body.
Surface irregularities
All surfaces, when zoomed into a microscopic level, contain hills and valleys that interlock when they move or rub on top of each other.
This unevenness of the surface is called surface irregularities or roughness.
Rough surfaces have larger irregularities, while smoother surfaces have lesser irregularities.
Nature of surface in contact
Friction depends on how hard the two surfaces are pressed together; as more surfaces are in contact and more bonds are formed→ more bonds to break → means more friction.
Only the normal reaction force (exactly perpendicular ) to the two surfaces increases friction.
Drag force
The frictional force exerted by fluids is called drag.
The drag force on an object depends on speed as well as the shape of the body and the nature of the fluid.
Kinetic Friction
The friction that comes into play when objects are in motion is called as kinetic friction.
