1. Fill in the blanks.
(a) Friction opposes the between the surfaces in contact with each other.
(b) Friction depends on the of surfaces. (c) Friction produces .
(d) Sprinkling of powder on the carrom board friction. (e) Sliding friction is than the static friction.
2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.
(a) rolling, static, sliding (b) rolling, sliding, static (c) static, sliding, rolling (d) sliding, static, rolling
3. Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be (a) wet marble floor, dry marble floor, newspaper and towel.
(b) newspaper, towel, dry marble floor, wet marble floor. (c) towel, newspaper, dry marble floor, wet marble floor (d) wet marble floor, dry marble floor, towel, newspaper
4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
5. You spill a bucket of soapy water on a marble floor accidentally.
Would it make it easier or more difficult for you to walk on the floor? Why?
6. Explain why sportsmen use shoes with spikes.
7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
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.
1.
(a) Friction opposes the motion between the surfaces in contact with each other.
(b) Friction depends on the nature of surfaces. (c) Friction produces heat.
(d) Sprinkling of powder on the carrom board reduces friction. (e) Sliding friction is less than the static friction.
2.
(c) static, sliding, rolling
Static friction comes into play when we try to move an object which is at rest. Sliding friction/kinetic friction acts on a body when it is moving. In case of rolling friction, the area of contact is smallest as compared to static or sliding friction. Hence, rolling friction has the least value. Thus, the correct sequence is—static, sliding, rolling.
3.
(a) wet marble floor, dry marble floor, newspaper and towel
The friction force depends on the nature of contact surfaces. If the surface is rough, more friction is present compared to smooth surfaces. Hence, the correct sequence of these surfaces when
towel.
4.
When a book slides down a table, the direction of frictional force on the book is opposite to the direction of its motion and along the incline as shown in t
It would be difficult to walk on the floor if we spill a bucket of water on the marble floor because it reduces the friction between the ground and feet.
6.
Spikes on shoes provides better grip while running because the frictional force between the ground and shoes increases with the help of spikes.
7.
Seema must apply larger force to push the heavier box because
9.
10.
required to overcome the interlocking is more in case of the heavier box.
Friction forces comes into play when irregularities present in the surface of the two objects in contact gets interlocked with each other. When an object is in motion, the sliding friction is smaller than the static friction as the interlocking during motion is very small. Thus, sliding friction is less than static friction.
Advantages:
(i) Friction helps in walking.
(ii) Friction is present between the tip of pen and a paper which allows us to write.
Limitations:
(i) Wear and tear of shoes
(ii) In heavy machines, heat is produced in a large quantity which can damage the machines. Thus, we use lubricants to reduce the friction and carry out heat.
When an object moves in fluid, fluid friction opposes the motion. So, to reduce the friction between object and fluids, the object is given special shape known as streamlined sha
