Even those surfaces which appear very smooth have a large number of minute irregularities on them (Fig. 9.5). We see that the friction is caused by the interlocking of irregularities in the two surfaces. It is obvious that the force of friction will increase if the two surfaces are pressed harder. You can experience it by dragging a mat when nobody is sitting on it, and when a preson is sitting on it. Make an inclined plane on a smooth floor, or on a table. You may use a wooden board supported by bricks, or books.
When we attempt to move any surface, we have to apply a force to overcome interlocking. On rough surfaces, there are a larger number of irregularities. So the force of friction is greater if a rough surface is involved.
Sample Paper all are made available through the best app for CBSE students and myCBSEguide website. Question 2.Ram and Shyam while returning from school saw a labour pushing hard to move a heavy box. (b) Friction depends on the _____________ of surfaces.
Factors such as friction, air resistance, and gravity can also influence the object's change in speed. 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. Friction comes into play when irregularities present in the surface of two objects in contact get interlocked with each other.
Friction Class 8 Extra Questions Very Short Answer Questions
- (b) Friction depends on the _______________________of surfaces.
- Have you ever thought why the sole of your shoe is grooved?
- As you have seen in the previous section, friction is desirable in some situations.
- Imagine that friction suddenly vanishes.
- In science, the common name of gases and liquids is fluids.
- (a) Friction opposes the _______________________between the surfaces in contact with each other.
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Have you ever thought why the sole of your shoe is grooved [Fig. It wears out the materials whether they are screws, ball bearings or soles of shoes (Fig. 9.8). Spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring which gets stretched when a force is applied to it.
What could you do to either increase or decrease the amount of friction?
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. The frictional force on an object in a fluid depends on its speed with respect to the fluid.
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You must have seen attaches and other pieces of luggage fitted with rollers. Even a child can pull such pieces of luggage (Fig. 12.14). Friction can never be entirely eleminated. No surface is perfectly smooth. Some irregularities are always there. (b) Friction depends on the _______________________of surfaces.
It provides the necessary grip between your shoe and the ground to propel you forward. Imagine that friction suddenly vanishes. Give examples to show that friction is both a friend and a foe. (a) Friction opposes the _____________ between the surfaces in contact with each other.
In fact, when a machine is operated, heat generated causes much wastage of energy. We shall discuss the ways of more information minimising friction in the following section. The match box will start falling down due to gravity.