Different Methods of Increasing and Reducing Friction

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What are the ways of Increase and Decrease Friction

In some cases friction is useful to us. In such cases we even want to increase friction to make it more useful to us. Friction can be increased by making the surface of an object ‘rough’. The surfaces of objects can be made rough in many ways depending on the situation where these objects are to be used. Before we discuss the methods of increasing friction, we should know the meaning of the terms ‘grooves’ and ‘treads’. A long and shallow cut or depression in the surface of a hard material is called groove. A series of patterns made into the surface of a tyre (to provide grip on the road) is called tread. Friction can be increased by the following methods.

1. Grooves Are Made in the Soles of Shoes to Increase Friction and Prevent Slipping

If we observe the soles of our shoes, we will find that some grooves have been made in the soles by the makers of shoes (see Figure). The grooves are made in the soles of shoes to increase friction with the ground (or floor) so that the shoes get a better grip even on a slippery ground and we can walk safely (without the risk of slipping).

2. Treads are Made in the Tyres of Vehicles to Increase Friction and Prevent Skidding of Vehicles on Wet Roads

When a road is wet (as during rains), there is a layer of water on the roads. The presence of water on the surface of road reduces friction between the tyres of vehicle and the surface of road due to which tyres lose their grip on the road. The reduced friction between tyres and road increases the chances of skidding of vehicle on wet road (especially when brakes are applied suddenly). Due to this it becomes difficult to control the running vehicle on a wet road. The treads on the surface of tyres are designed in such a way that they push away water from under the tyre (as the tyre rolls over a wet road) (see Figure).

When water is pushed away from the surface of road beneath the tyre, friction between road and tyre increases and improves the tyre’s grip on the wet road. The risk of skidding of a fast running vehicle is very much reduced. Thus, the treaded tyres of cars, buses, trucks, motor cycles, scooters and bicycles provide better grip on the road (especially on wet and slippery road). The treads of tyres do not help much in dry weather.

3. Spikes are Provided in the Shoes of Players and Athletes to Increase Friction and Prevent Slipping

The players and athletes have to run fast. So, greater friction is required between the soles of their shoes and ground to prevent slipping. To increase friction, spikes are provided in the soles of shoes worn by players and athletes (see Figure). Spikes are the pointed nails which get into the ground and increase friction between shoe and the ground. This prevents the slipping of player or athlete on running.

4. Gymnasts Apply Some Coarse Substance on Their Hands to Increase Friction for Better Grip

Kabaddi players rub their hands with dry soil to increase friction and get a better grip on their opponent players (so that they may not slip out of hands).

5. Machine Belts are Made of Special Materials to Increase Friction and Drive Machine Wheels Properly

In many machines (like flour mills), belts are used to drive wheels for running the machines. Greater friction is required between the belts and machine wheels so that the belts can drive machine wheels properly without slipping off the wheels. To increase friction, the machine belts are made of special materials having rough surfaces.

Methods Of Reducing Friction

In some cases friction is harmful to us. In such cases, we wish to reduce friction so as to make it less harmful to us. For example, friction between the moving parts of machines causes a lot of wear and tear to the machine parts. It also leads to the production of undesirable heat and loss of energy. So, we should make efforts to reduce the friction (or minimise the friction) so as to prevent much damage. Friction can be reduced by the following methods.

1. Friction Can be Reduced by Making the Surfaces Smooth by Polishing

We know that friction is due to the roughness of surfaces. So, if we make the surfaces smooth by polishing, then friction will be reduced. For example, a slide in the park is polished to make its surface smooth and reduce friction. Due to reduced friction of a polished, smooth slide, children can slide down easily (see Figure). However, even highly polished objects look rough when seen through a microscope, so there is always some friction even on polished objects.

2. Friction Can be Reduced by Applying Lubricants (like Oil or Grease) to the Rubbing Surfaces

Friction between two surfaces in contact with each other is due to the interlocking of uneven surfaces having irregularities on them [as shown in Figure]. When oil or grease is applied between the moving parts of a machine, a thin layer of oil (or grease) is formed between the two rubbing surfaces.

This layer of oil separates the two rubbing surfaces a little bit due to which their interlocking is reduced to a large extent [see Figure], Since the applying of oil (or grease) helps in avoiding interlocking between the two rubbing surfaces to a large extent, friction is reduced and movement becomes smooth. In fact, when oil or grease is applied to the moving parts of a machine, then their surfaces do not rub directly against each other, they rub through a layer of oil or grease (which is very smooth).

The substances which reduce friction are called lubricants. Oil, grease, graphite and fine powder are lubricants. The applying of lubricants (such as oil, grease, etc.) to a machine is called lubrication. A lubricant (like oil) reduces friction by helping the surfaces slide over each other smoothly. Thus, friction can be reduced by lubrication. Machines are lubricated with oil or grease to reduce friction. A well lubricated machine runs more smoothly and lasts longer.

A bicycle mechanic and a motor mechanic uses grease between the moving parts of these machines to reduce friction and increase efficiency. Sometimes the hinges of a door make rattling noise when we open or close the door (due to increased friction caused by rusting). When a few drops of oil are poured on the hinges of a door, the friction is reduced and the door moves smoothly (without making any noise). We sprinkle fine powder as ‘dry lubricant’ on a carrom board to reduce friction. Please note that though we can reduce friction but we cannot make it zero (or nil) even if the surfaces are highly polished or large amounts of lubricants are applied. Friction can never be entirely eliminated.

In some machines, it may not be advisable to use oil, etc., as lubricant. In such machines, an air cushion between the moving parts is used to reduce friction. For example, the frictional drag from the sea on a hovercraft is reduced by a cushion of compressed air (A vehicle or craft which travels over land or water on a cushion of air provided by a downward blast, is called a hovercraft).

3. Friction Can be Reduced by Using Wheels to Move Objects

It is quite difficult to move a heavy suitcase by dragging it on the ground because the sliding friction between the heavy suitcase and the ground is very large. Now, if this heavy suitcase is fitted with small wheels (called rollers), then it can be pulled very easily. This is because when we attach wheels, then sliding friction is converted into rolling friction. And rolling friction between the wheels of suitcase and the ground is much less.

Thus, friction can be reduced by attaching wheels (or rollers) to a heavy suitcase (or any other heavy object which is to be moved). Due to very small rolling friction, even a child can pull a heavy suitcase fitted with small wheels (or rollers) (see Figure). From this discussion we conclude that friction can be reduced by attaching wheels to move the objects. So, wheels are often used to reduce friction. In fact, all the moving vehicles (like bicycles, cars, buses and trucks, etc.) are fitted with wheels to reduce friction with the road (so that they can move easily).

Before we go further, we should know the meaning of the device called ‘ball bearing’. Ball bearing is a device which consists of a ring of small metal balls (see Figure). The small metal balls of a hail bearing can roil freely. Ball bearings are designed to make the moving parts of a machine to roll over each other rather than slide. The ball bearing is introduced between the two surfaces which have to rotate over each other. For example, the axle is fixed on the inner side of a ball bearing and wheel is fixed to the outer side of the ball bearing. The ball bearing reduces friction by making the two surfaces (axle and wheel) to roll over each other. This happens due to the rolling action of small metal balls present inside the bail bearing.

4. Friction Can be Reduced by Using Bali Bearings Between the Moving Parts of Machines

We have just studied that friction can be reduced by using wheels. Even a wheel produces some friction where its central hole (or hub) rubs with the axle [see Figure]. To reduce friction still further, wheels are mounted on ‘ball bearings’. The ball bearing is fixed between the hub of wheel and axle.

When the wheel revolves, the balls of ball bearing roll and reduce friction [see Figure (b)], So, the use of ball bearing makes the wheel roll smoothly over the axle. Since rolling friction is much smaller than the sliding friction, sliding friction is replaced in most of the machines by rolling friction by using ball bearings. Thus, in most of the machines, friction is reduced by using ball bearings. For example, the wheels of a bicycle turn on sets of ball bearings. These ball bearings reduce friction because they roll rather than slide. Ball bearings are used between the hubs and axles of machines such as bicycles, motor cars, and ceiling fans, etc., (to reduce friction).