NCERT Solutions For Class 8 Science Chapter – 12 Friction
Q1. Fill in the blanks.
- Friction opposes the _______ between the surfaces in contact with each other.
- Friction depends on the ______ of surfaces.
- Friction produces_______.
- Sprinkling of powder on the carrom board ______ friction.
- Sliding friction is _________ than the static friction.
Answer:-
- Motion
- Nature
- Heat
- Reduces
- Less
Q2. Four children were asked to arranged forces due to rolling , static and sliding d=frictions in a descending order. Their arrangements are given below. Choose the correct arrangement.
- Rolling,static,sliding
- Rolling,sliding,static
- Static,sliding,rolling
- Sliding,static,rolling
Answer:-
C is the correct option.
Q3. 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
- Wet marble floor, dry marble floor, newspaper and towel.
- Newspaper , towel and dry marble floor , wet marble floor.
- Towel,newspaper,dry marble floors, towel , newspaper
- Wet marble floor , dry marble floor , towel , newspaper.
Answer:-
The force of friction acting on the car different surfaces in increasing order will be wet marble road,dry marble floor , newspaper and towel Therefore (a) is the correct answer.
Q4. Suppose your writing desk a titled a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Answer:-
The frictional force will be opposite to the directions of motion.
Q5. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you walk on the floor? Why?
Answer:-
It would make it more difficult for us to walk on the marble floor since the frictional force work would further decreases and thus our grip on the floor while walking would become even lesser.
Q6. Explain why sportsmen use shoes with spikes.
Answer:-
Sportsmen use shoes with spikes to increase the grip between their feet and the ground by increasing the friction with the help of spikes. This aids them while running on the ground
Q7. Iqbal has to push a lighter box and Seema has to push similar heavier box on the same floor Who will have to apply a larger force and why ?
Answer:-
Seema would have to apply a larger forces as she would have to overcome a greater frictional force. The frictional force between two surfaces exists due to the interlocking of the irregularities on the surface. The magnitude of this frictional force depends on how tight his interlocking is which in this case depends on the weight of the boxes which is more in case of Seema.
Q8. Explain why sliding friction is less than static friction.
Answer:-
Sliding friction is less than static friction as the frictional force between two surfaces depends on the interlocking between the irregularities on the surface. This interlocking in case of sliding decreases as the contact points does not get enough time to interlock properly thus reducing the frictional force.
Q9. Give examples to show the friction is both as friend and foe.
Answer:-
Friction acting as a friend:
- It aids us to walk and cars to move on the roads.
- Fire can be ignited using functions.
Friction acting as s foe:
- It causes the efficiency of engines to decreases and also damages machinery.
- Friction cause soles of shoe and tries to wear off.
Q10. Explain why objects moving in fluids must have special shapes.
Answer:-
When an object is moving through a liquid there is an opposing force offered by the liquid against the motion of the object. To reduce this opposing force object must have special shapes.