FRICTION CLASS-VII

 worksheet-I

 1 Explain Why, it is easier to drag a mat on floor when nobody is sitting on it but much more difficult to drag the same mat when a person is sitting on it.
2 Which type of surfaces produce {a} least friction, and {b} too much friction? What is the direction of force of friction acting on a moving object?
3  Why do kabaddi players rub their hands with dry soil?
4 Why are cars, airplanes & rockets streamlined?
5  What is the special name of frictional force exerted by fluids (like air or water)? 
 6. What are the factors that affect the fluid friction?7
7  What is the name of ‘special shape’ which is given to objects moving through fluids to reduce drag? 
8 Fill in the blanks:
(a) Sprinkling of powder on the carom board ………………. Friction.
 
(b) Ball bearings reduce friction because they …………………rather than slide. 
9 Two men tried to push a heavy box & could  not succeed. Finally wheels were fitted to the box & now a single man could move it. Justify. 
10.  What prevents you from slipping every time you take a step forward?
11 What happens when you rub your hands vigorously for a few seconds? Why does this happen?
12. Explain why:
(a) a pencil will write on paper but not on glass
(b) The handles of motor cycle are covered with a rubber sheet with spikes.(c) The soles of our shoes wear out gradually.
(d) Tyres of car wear out gradually.