In fact, all vehicles are designed to have shapes which reduce fluid friction. Common examples are the use of ball bearings between hubs and the axles of ceiling fans and bicycles (Fig. 9.16). Friction in order to increase efficiency. Friction is caused by the irregularities on the two surfaces in contact. Even those surfaces which appear very smooth have a large number of minute irregularities on them (Fig. 12.5). Irregularities on the two surfaces lock into one another.
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In some machines, it may not be advisable to use oil as lubricant. An air cushion between the moving parts is used to reduce friction. We deliberately increase friction by using brake pads in the brake system of bicycles and automobiles. When you are riding a bicycle, the brake pads do not touch the wheels. But when you press the brake lever, these pads arrest the more information motion of the rim due to friction. You might have seen that kabaddi players rub their hands with soil for a better grip of their opponents.
It can help determine the coefficient of friction between different materials. 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.
- Similarly, water and other liquids exert force of friction when objects move through them.
- In some machines, it may not be advisable to use oil as lubricant.
- Does it depend on the smoothness of the surfaces?
- In some situations, I oppose the motion in other situations, I facilitate the motion but, I always oppose the relative motion between two moving surfaces.
- Now spread a piece of clothover the table.
- (a) Friction opposes the _____________ between the surfaces in contact with each other.
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Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force. In sports such as ice skating and skiing, friction is minimized to enable smoother movement, enhancing performance. Visit a shop which sells sports shoes. Observe the soles of shoes meant for various sports. If an object started moving, it would never stop if there were no friction.
h Class Physics 2nd Lesson Friction Questions and Answers (Exercise)
Does it depend on the smoothness of the surfaces? (d) Sprinkling of powder on the carrom board _______________________friction. Yes, traction is affected by friction. Friction between a surface and an object can either increase or decrease the traction, depending on the circumstances. More friction typically means better traction, while less friction can lead to reduced traction. To download Printable worksheets for class 8 Mathematics and Science; do check myCBSEguide app or website.
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How can increase friction on a moving object?
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Since the rolling friction is smaller than the sliding friction, sliding is replaced in most machines by rolling by the use of ball bearings. Common examples are the use of ball bearings between hubs and the axles of ceiling fans and bicycles (Fig. 12.16). It is obvious that when objects move through fluids, they have to overcome friction acting on them.
The frictional force also depends on the shape of the object and the nature of the fluid. The frictional force exerted by fluids is also called drag. As you have seen in the previous section, friction is desirable in some situations.
You must have seen worn-out steps of foot over-bridges at railway stations. 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. In some situations, I oppose the motion in other situations, I facilitate the motion but, I always oppose the relative motion between two moving surfaces. Put some lubricant, and I become small there.
Put a mark with a pen at any point A on the inclined plane. Now let a pencil cell move down from this point. How far does it move on the table before coming to rest? Now spread a piece of cloth over the table. Make sure that there are no wrinkles in the cloth. (a) wet marble floor, dry marble floor, newspaper and towel.
When the box starts sliding, the contact points on its surface, do not get enough time to lock into the contact points on the floor. The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction. On the other hand, the force required to keep the object moving with the same speed is a measure of sliding friction.