Friction - Class 8 - Science
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Back Questions - Friction | NCERT | Science | Class 8
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
(a) Friction opposes the relative motion between the surfaces in contact with each other.
(b) Friction depends on the nature and texture 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.
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
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Sign up nowAlida runs her toy car on a 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
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Sign up nowSuppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of the frictional force acting on it.
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Sign up nowYou spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?
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Sign up nowExplain why sportsmen use shoes with spikes.
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Sign up nowIqbal 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?
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Sign up nowExplain why sliding friction is less than static friction.
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Sign up nowGive examples to show that friction is both a friend and a foe.
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Sign up nowExplain why objects moving in fluids must have special shapes.
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Sign up nowExtra Questions - Friction | NCERT | Science | Class 8
Sometime, a crackling sound is heard while taking off a sweater during winters. Explain.
When a sweater is removed, friction occurs between the woollen fibers of the sweater and the skin. This friction generates static electricity, causing the sweater to become charged. As a result of this charging, one can often hear a crackling sound. This sound is the result of the discharge of built-up static electricity.
A hockey player pushes the ball on the ground. It comes to rest after travelling a certain distance because:
A. The ball moves only when pushed.
B. The opposing force of friction acts on the ball.
C. The player stops pushing the ball.
D. No unbalanced force acts on the ball.
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Sign up nowFor the toppling of the hexagon as shown in the figure, the coefficient of friction must be
A) $>0.21$
B) $<0.21$
C) $=0.21$
D) $<0.21$
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Sign up nowQ: You are a sixth-year graduate student at a large university in the final months of your dissertation research on novel photonic materials. You are worried about your next appointment and have applied for several postdoctoral positions in this field plus a few tenure-track assistant professorships at universities where you would like to work. To your surprise and pleasure, you are invited for an interview for a tenure-track appointment at your undergraduate alma mater, a prestigious research institution in a city where you already have connections and would love to live.
In the question-and-answer period following your seminar on your research, the department chair asks for detailed information about the novel material preparation technique developed in your graduate research and used extensively in your experiments. Your group is working on a patent application, and its members have agreed not to provide details until a paper currently being prepared is submitted for publication. Your thesis advisor will be giving the first major presentation on the technique at a major international conference in a couple of months.
You answer that you and your colleagues are in the process of writing it up for publication and a patent application, and you would be glad to send them an early preprint when it is available. The question-and-answer period continues and concludes uneventfully and pleasantly. After the seminar, in your private interview with the Chair, he pushes harder for this information, remarking that the Department seeks team players willing to share information with department colleagues and referring to your undergraduate roots and the need to prove you are one of them to be a viable candidate for the position.
s:
- What are the interests of the various players?
- Where are there conflicts of interest?
- What are your options? What should you do?
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Sign up nowLong Questions - Friction | NCERT | Science | Class 8
This chapter discussed the force of friction and its effects on different surfaces. Can you illustrate with suitable examples how friction plays a crucial role in our day-to-day life? Discuss its advantages and disadvantages.
Friction plays a crucial role in our daily life. For instance, friction between our shoes and the ground allows us to walk or run without slipping. Similarly, friction between the tyres of a vehicle and the road helps in movement, turning, and stopping the vehicle efficiently. Gymnasts apply coarse substances to their hands to increase grip while performing, again highlighting the importance of friction. Despite its benefits, friction also has downsides, which denotes it as a 'necessary evil'. It leads to wear and tear of objects such as soles of shoes and machinery parts, causing wastage. Also, friction can create undesired heat, as seen when we rub our palms together vigorously or run a mixer for an extended duration.
The force of friction varies depending on the type and nature of the surfaces in contact. Describe with examples how friction changes based on whether the surfaces are smooth, rough, or lubricated. How can one type of friction be converted into another to increase efficiency in machines or reduce wear and tear?
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Sign up nowShort Questions - Friction | NCERT | Science | Class 8
Why is it easier to roll a heavy object than to slide it over another?
It is easier to roll a heavy object than to slide it over another surface because the force needed to overcome rolling friction is less than the force needed to overcome sliding friction. This is because when an object rolls, the contact points on its surface do not get enough time to lock into the contact points on the other surface, reducing the friction.
How does the surface of an object affect the force of friction between it and another surface?
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Sign up nowWhy does an object in motion stop when no external force is applied on it?
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