CBSE – 8th Standard Science

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Friction

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

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  • The force of friction always opposes the applied force.

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  • 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

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  • 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.

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  • 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

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