9.4. Increasing and Reducing Friction

As you have seen in the previous section, friction is desirable in some situations. Have you ever thought why the sole of your shoe is grooved? It is done to provide the shoes better grip on the floor, so that you can move safely. Similarly, the treaded tyres of cars, trucks, and bulldozers provide better grip with the ground.

Friction is a force that opposes motion, and in many situations, it is necessary and beneficial. For instance, the grooves on the soles of shoes and the tread patterns on vehicle tyres are designed to increase friction. This helps us to walk safely and vehicles to maintain better traction on the road. Without sufficient friction, we might slip and fall while walking or lose control of a vehicle.

Think about the way you walk on a smooth, polished floor versus a rough concrete path. On the concrete, you feel stable because of the increased friction that helps you to grip the surface better. If the surfaces were too smooth like ice, walking would be extremely challenging.

In some situations, however, friction is undesirable and we would want to minimize it. Why do you sprinkle fine powder on the carrom board? You might have noticed that when a few drops of oil are poured on the hinges of a door, the door moves smoothly. A bicycle and a motor mechanic uses grease between the moving parts of these machines. In all the above cases, we want to reduce friction in order to increase efficiency.

While friction can be beneficial, there are also times when we want to reduce it. For example, on a carrom board, fine powder is sprinkled to create a smooth surface that allows the coins to slide easily. Similarly, applying oil or grease to machinery helps the parts to move without grinding against each other, which increases efficiency and performance. Reducing friction in these cases saves energy and helps prolong the life of equipment.

Imagine trying to push a heavy drawer. When it's dry, it might stick and be tough to open. But if you add a little oil to the sliding parts, it opens easily. This is because you've reduced the friction between the drawer and its tracks.

When oil, grease, or graphite is applied between the moving parts of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other. Interlocking of irregularities is avoided to a great extent. Movement becomes smooth. The substances which reduce friction are called lubricants.

Lubricants are materials like oil, grease, or graphite that help reduce friction between surfaces in contact. When these substances are applied, they create a layer that prevents the surfaces from pressing against each other directly. This minimizes wear and tear on the materials and allows for smoother operation of machinery and tools.

Think of a bicycle chain. If the chain is rusty and dry, it creaks and makes pedaling harder. But if you apply some lubricant to the chain, it glides smoothly, making it easier for you to ride. This is because the lubricant reduces the friction between the moving parts of the chain.

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 motion of the rim due to friction. The wheel stops moving.

Brake systems are designed to create a significant amount of friction to stop moving vehicles effectively. When the brake pads are pressed against the wheels, they create a high friction force that slows down and eventually stops the wheel's motion. This ability to control speed and stop is critical for safe driving.

Think about riding your bicycle downhill. If you want to slow down or stop, you pull the brakes, which pushes the pads against the wheel. The friction from the pads quickly reduces the wheel's speed. This shows how we use friction deliberately to increase control over movement.

You might have seen that kabaddi players rub their hands with soil for a better grip of their opponents. Gymnasts apply some coarse substance on their hands to increase friction for better grip.

In sports, athletes often need to enhance their grip to perform better. Kabaddi players use soil to increase friction with their opponents, preventing slipping and allowing for better handling. Similarly, gymnasts use chalk or other coarsely textured substances to increase the friction between their hands and the equipment, helping them to grip securely while performing stunts or routines.

Consider a rock climber who needs to maintain a solid grip on a rocky surface. The climber might use chalk to dry their hands and improve grip strength, which enables them to hold onto tiny ledges. This is a perfect example of how increasing friction can be crucial for success in athletic activities.

Activity 9.4: Take a few pencils which are cylindrical in shape. Place them parallel to each other on a table. Place a thick book over it. Now push the book. You observe the pencils rolling as the book moves. Do you feel it easier to move the book in this way than to slide it? Do you think that the resistance to the motion of the book has been reduced?

This activity demonstrates how rolling objects can reduce friction compared to sliding. By placing cylindrical pencils under a book, you create a situation where the book rolls rather than slides, significantly reducing the frictional force encountered. This principle is applied in various machines to facilitate smoother movement and reduce energy consumption.

Picture yourself trying to move a heavy box by sliding it across a floor. It feels very heavy, right? Now imagine using a tube to roll it instead. It's much easier to push the box using the tube because rolling reduces friction. This idea is why we have wheels on vehicles; they allow for easier movement by minimizing resistance.

You know that air is very light and thin. Yet it exerts a frictional force on objects moving through it. Similarly, water and other liquids exert force of friction when objects move through them. In science, the common name for gases and liquids is fluids.

Fluid friction occurs when objects move through liquids or gases. This resistance, called drag, depends on the object's speed, shape, and the type of fluid it moves through. Understanding fluid friction is essential for designing vehicles, athletes’ gear, and even ships, as we want them to minimize energy loss during motion.

When you're swimming, you may notice that moving through water is harder than moving through air. This is because water is denser than air, which means you experience more fluid friction while swimming. Swimmers often streamline their bodies and wear fitted suits to reduce this friction and move more efficiently through the water.

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