AP State Board new syllabus 8th Class Physics Guide 2nd Lesson Friction Textbook Exercise Questions and Answers.
AP 8th Class Physical Science 2nd Lesson Questions and Answers Friction
8th Class Physics 2nd Lesson Friction Questions and Answers (Exercise)
Question 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.
Answer:
a) motion
b) Irregularities or nature
c) heat
d) reduces
e) smaller (lesser)
Question 2.
Four children were asked to arrange forces due to rolling, static and sliding frictions in 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
Answer:
(c) static, sliding, rolling
Friction comes into play when irregularities present in the surface of two objects in contact get interlocked with each other. Static friction comes into play when we try to move an object which is at rest. Sliding friction, comes into play when an object slides over the surface of another object.
In sliding friction, the time given for interlocking is very small, hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Because of this reason, sliding friction is less than static friction.
Similarly, the area of contact in case of rolling friction is smallest as compared to static or sliding friction. This area of contact changes gradually because of rolling. Hence, rolling friction is lesser than both static and sliding friction.
Question 3.
Alida runs her toy car on the 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.
Answer:
(a) wet marble floor, dry marble floor, newspaper and towel.
Force of friction depends on the nature of surfaces in contact. The rougher the surface, the more is the friction between the surfaces in contact and vice-versa. Roughness present in the given surfaces can be arranged in an ascending order as wet marble floor, dry marble floor, newspaper and towel.
Hence, the correct sequence of these surfaces when arranged according to the increase in the force of friction acting on the car is – wet marble floor, dry marble floor, newspaper and towel
Question 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.
Answer:
When a book slides on the writing desk, a frictional force acts between the book and the surface of the desk. The direction of frictional force on the book is opposite on the direction of its motion and acts in upward direction, as shown in the following figure.
Question 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?
Answer:
We are able to walk because of the friction present between our feet and the ground. In order to walk; we push the ground in the backward direction with our feet. The force of friction pushes it in the forward direction and allows us to walk. The force of friction between the ground and feet decreases when there is soapy water spilled on the floor. Hence, it becomes difficult to walk on the soapy floor.
Question 6.
Explain why sportsmen use shoes with spikes.
Answer:
Sportsmen use shoes with spikes because of the better grip given by spikes while running. This is because the force of friction between the shoes and the ground increases with the help of spikes.
Question 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?
Answer:
Force of friction arises because of interlocking of irregularities on the two surfaces in contact. When a heavy object is placed on the floor, the interlocking of irregularities on the surfaces of box and floor become strong.
This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus, to push the heavier box, Seema has to apply a greater force than Iqbal.
Question 8.
Explain why sliding friction is less than static friction.
Answer:
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. Therefore less force is required to over come this interlocking. Because of this reason, sliding friction is less than static friction.
Question 9.
Give examples to show that friction is both a friend and a foe.
Answer:
Advantages of friction :
- We are able to walk because of friction.
- Friction between the tip of the pen and a paper allows us to write.
Disadvantages of friction :
- Tyres and soles of shoes wear out because of friction.
- Friction between the different parts of machines produces heat. This can damage the machines.
Question 10.
Explain why objects moving in fluids must have special shapes.
Answer:
When a body moves through a fluid, it experiences an opposing force which tries to oppose its motion through the fluid. This opposing force is known as the drag force. This frictional force depends on the shape of the body. By giving objects a special shape, the force of friction acting on it can be minimised. Hence, it becomes easier for the body to move through the fluid.
Extended Learning – Activities and Projects
Question 1.
What role does friction play in the sport of your choice? Collect some pictures of that sport in action where friction is either supporting it or opposing it. Display these pictures with proper captions on the bulletin board of your classroom.
Answer:
Activity for home.
Question 2.
Imagine that friction suddenly vanishes. How would life be affected. List ten such situations.
Answer:
If friction vanishes :
- we will not be able to walk on the roads
- vehicles on the roads may slip
- we cannot write on the paper or blackboard
- we cannot stop vehicles by applying brakes
- nails and screws will not work
- no moving object will come to a halt
- objects will not remain standing at their places
- we cannot stand on a floor
- buildings will not remain intact at their places
- no painting and drawings can be made.
Question 3.
Visit a shop which sells sports shoes. Observe the soles of shoes meant for various sports. Describe your observations.
Answer:
Different sports shoes have different kinds of soles eg.
- Running shoes : are equipped with soles that provide cushion, stability, flexibility and traction.
- Field sports : Soccer, baseball, football shoes are spiked or created with varying formations.
- Court sports : Tennis and Volleyball shoes require durable and supportive soles with plenty of traction for gripping on the court. They must provide maximum shock absorption.
- Cycling: Cycling shoes have stiffer soles for efficient energy transfer when pedalling.
4. A toy to play with :
Take an empty match box. Take out its tray. Cut a used refill of a ball pen of the same width as the tray as shown in the figure below. Fix the refill with two pins on the top of the tray as shown in figure. Make two holes on the opposite sides of the tray.
Make sure that the holes are large enough to allow a thread to pass through them easily. Take a thread about a metre long and pass it through the holes as shown. Fix beads at the two ends of the thread so that it does not come out. Insert the tray in the outer cover of the matchbox.
Suspend the matchbox by the thread. Leave the thread loose. The matchbox will start falling down due to gravity. Tighten the thread now and observe what happens. Explain your observation. Can you relate it to friction?
Answer:
The match box will not fall further due to the friction between thread and the match box.
8th Class PS 2nd Lesson Questions and Answers (Lab Activities)
Activity – 1
1. Gently push a book on a table, you will notice that the book stops after some distance. Now push the book from the opposite side, and note your observation.
Answer: Observation : The book stops moving after some time.
Conclusion : A frictional force acts on the book from the opposite direction and slows down the movement of the book, and it finally stops. Force of friction always opposes the motion of an object or prevents a stationary object from moving.
Activity – 2
2. Tie a string around a brick. Pull the brick by a spring balance. Now repeat the same by wrapping the brick with a polythene sheet. Note the reading in the spring balance. Was there a difference in the reading in both the cases?
Answer:
Observation : The force required to pull the brick without the polythene bag was more than that of the brick with polythene bag. This is because the surface of the brick became smooth with the polythene bag. Therefore, less force was required to pull it.
Conclusion : Smooth surfaces offer less friction than rough surfaces. Frictional force depends on the nature of two surfaces in contact.
Activity – 3
3. Make an inclined plane on smooth floor, or on a table. Use a wooden board as inclined floor. Put a mark at any point ‘A’. Now. let a pencil cell move down from this point. Note down the distance travelled by the ball from the bottom of the inclined plane to point where it comes to a stop.
Now, spread a cloth over the floor. Try again with pencil cell and note down the distance.
Answer:
Observation : The distance covered by ball in two cases are different. When there is no cloth on the floor pencil cell covered maximum distance.
Conclusion : The friction offered by different surfaces are different.
Activity – 4
4. Take a few pencils which are cylindrical in shape. Place them parallel to each other on a table. Place a thick book over it now push the book. What is your observation?
Answer:
Observation : You observe the pencils rolling as book moves. You feel it easier to move the book in this way than to slide it.
Conclusion : The rolling friction is smaller than the sliding friction.