8. Explain why sliding friction is less than static friction.
9. Give examples to show that friction is both a friend and a foe.
10. Explain why objects moving in fluids must have special shapes.
Answers
Explanation:
8.Friction comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other. In sliding, the time given for interlocking is very small. Hence, interlocking is not strong. ... Because f this reason, sliding friction is less than static friction.
9.Friction is friend (Advantages) :
(i) Friction allows us to grip and catch different objects.
(ii) It helps us to walk comfortably on the surface.
(iii) It helps to minimise the speed or to stop the moving objects.
(iv) It helps us to write on paper or blackboard.
(v) The things do not move from their places due to friction.
Friction is foe (Disadvantages) :
(i) Friction causes wear and tear in objects.
(ii) It causes damage the parts of machines.
(iii) The machines or tools require regular maintenance due to which a lot of money is wasted.
(iv)It reduces the speed of moving objects so more force is required.
(v)It does not allow the free movement of objects.
10.Moving objects in fluid must have special shapes because the drag force or the friction force depends of the shape of the object. Special shapes are designed to minimize the opposing frictional force.
Answer:
8.sliding friction is less than static friction because sliding friction acts on a body which is in motion but the body continues to move , but static friction acts on a resting or stationary body , it prevents the body from moving .
so , static friction is more than sliding friction.
9. friction as friend:
i)we are able to walk without falling down.
ii) objects kept on a table doesn't slide and fall down due to friction.
friction as foe:
i) friction makes it hard to move a heavier object.
ii) it causes objects wear and tear.