# CBSE – 8th Standard Science

## Friction

• Friction is caused by the irregularities on the two surfaces in contact

• The force of friction always opposes the applied force.

• Spring Balance is a device used for measuring the force acting on an object.
• In spring balance stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.
• Friction is caused by the irregularities on the two surfaces in contact.
• Force of friction will increase if the two surfaces are pressed harder.
• The force required to overcome friction at the instant an object starts moving from    rest is a measure of static friction.
• If an object started moving, it would never stop if there were no friction.
• The sliding friction is slightly smaller than the static, any object started moving, it would never stop if there were no friction.
• Friction can also produce heat.
• The substances which reduce friction are called lubricants.
• Friction can never be entirely eliminated. No surface is perfectly smooth. Some irregularities are always there.
• To reduce friction in order to increase efficiency. oil, grease or graphite is applied

• When one body rolls over the surface of another, the resistance to motion is called the rolling friction. It reduces friction.
• Rolling reduces friction.
• It is always easier to roll than to slide a body over another. That is the reason it is convenient to pull the luggages fitted with rollers.
• Fluids exert force of friction on objects in motion through them. The frictional force exerted by fluids is also called drag.
• Fluids exert force of friction on objects in motion through them.
• The frictional force on an object in a fluid depends on its speed with respect to the fluid.
• Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.
• Friction depends on the nature of surfaces 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 press together.
• Static friction comes into play when we try to move an object at rest.
• Sliding friction comes with play when an object is sliding over another.

• Sliding friction is smaller than static friction.
• Friction can be increased by making a surface rough.
• Friction is important for many of our activities.
• The sole of the shoes and the tyres of the vehicle are treaded to increase friction.
• The friction is sometimes undesirable.
• Friction can be reduced by using lubricants.
• When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than the sliding friction.
• In many machines, friction is reduced by using ball bearings.
• Fluid friction can be minimized by giving suitable shapes to bodies moving in fluids.
• Even those surfaces which appear very smooth have a large number of minute irregularities on them Irregularities on the two surfaces lock into one another.
• You saw that if you apply the force along the left, friction acts along the right.
• Finally it stops. Have you not seen a moving ball on the ground stopping after some time? Why do we slip when we step on a banana peel.
• It is difficult to walk on a smooth and wet floor

## CBSE 8th Standard Science

CTN’s handcrafted quick & easy revision notes to help the students understand the concepts and revise the chapters.

You will also get comprehensive question bank which will not only help the student prepare for the exams, but also get also secure better grades and marks.

CBSE 8th Standard Science Syllabus and Revision Notes

• Crop Production & Management
• Microorganisms – Friends & Foe
• Synthetic, Fibers & Plastic
• Materials – Metals & Non-Metals
• Coal & Petroleum
• Combustion & Flame
• Conservation Of Plants And Animals
• Cell Structure And Functions
• Reproduction In Animals
• Reaching The Age Of Adolescence
• Force And Pressure
• Friction
• Sound
• Chemical Effects Of Electric Current
• Some Natural Phenomena
• Light
• Stars And The Solar System
• Pollution Of Air And Water

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