State one way of increasing the friction between two surfaces by ncrt
Answers
HERE ARE FOUR METHODS FROM NCERT:
1
Create a “rougher” or more adhesive point of contact. When two materials slide or rub against each other, three things can happen: small nooks, crannies, and irregularities on the surfaces can catch on each other; one or both surfaces can deform in response to the motion; and, finally, the atoms within each surface can interact with each other.[2] For practical purposes, all three of these effects do the same thing: generate friction. Picking surfaces that are abrasive (like sandpaper), deform when pressed (like rubber), or have adhesive interactions with other surfaces (like tacky glue, etc.) is a straightforward way to increase friction.
Engineering textbooks and similar resources can be great tools when picking which materials to use to generate high friction. Most standard building materials have known "friction coefficients" — that is, measures of how much friction they generate with other surfaces. Sliding friction coefficients for just a few common materials are listed below (higher coefficients indicate greater friction):
Aluminum on aluminum: 0.34
Wood on wood: 0.129
Dry concrete on rubber: 0.6-0.85
Wet concrete on rubber: 0.45-0.75
Ice on ice: 0.01
2
Press the two surfaces together harder. One fundamental principle of basic physics is that the friction an object experiences is proportional to its normal force (for our purposes, this is basically the force with which it presses into the object it's sliding against).[3] This means that the friction between two surfaces can be increased if the surfaces are pressed into each other with greater force.
If you've ever used a set of disc brakes (for instance, on a car or bike) you've observed this principle in action. In this case, pressing the brakes pushes a set of friction-generating pads into metal discs attached to the wheels. The harder the brakes are pushed, the harder the pads get pressed into the discs and the more friction is generated. This can stop the vehicle quickly, but can also release lots of heat, which is why a set of brakes is usually quite hot after heavy braking.
3
Stop any relative motion. That is, if one surface is in motion with respect to another, stop it. Up until now, we've focused on kinetic (or "sliding") friction — the friction that occurs between two objects or surfaces as they rub against each other. In fact, this friction is different from static friction — the friction that occurs when one object starts to move against another. Essentially, the friction between two objects is greatest right when they start moving against each other. Once they're already in motion, friction decreases. This is one of the reasons why it's harder to start pushing a heavy object than it is to keep moving it.[5]
Try this simple experiment to observe the difference between static and kinetic friction: place a chair or another piece of furniture on a smooth floor in your house (not rug or carpet). Make sure the furniture doesn't have protective "foot pads" or any other sort of material on the bottom that might make it easy to slide across the floor. Try to push the furniture just hard enough so that it starts moving. You should notice that as soon as the furniture starts moving, it immediately becomes slightly easier to push. This is because the kinetic friction between the furniture and the floor is less than the static friction.
4
Remove lubrication between the two surfaces. Lubricants like oil, grease, petroleum jelly, and so on can greatly reduce the friction between two objects or surfaces. This is because the friction between two solids is generally much higher than the friction between those solids and the liquid between them. To increase friction, try removing any lubricants from the equation, using only "dry", un-lubricated parts to generate friction.
To see the friction-reducing potential of lubricants, try this simple experiment: Rub your hands together as if they're cold and you want to warm them up. You should immediately notice them heat up from the friction. Next, put a fair amount of lotion in your palms and try the same thing. Not only should it be easier to rub your hands against each other quickly, but you should also notice much less heat.
There are two methods of increasing friction: one is by making the surfaces rough and the other by increasing the mass of the object that is moving. For example, the tyres of vehicles have treads (these are the 'designs' that you can see on the tyre surface), which increase the friction between the tyre and the road.