CBSE – 8th Standard Science

• 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