9.4 - Increasing and Reducing Friction

Friction is a force that opposes the relative motion or tendency of such motion of two surfaces in contact. There are situations where friction needs to be increased and others where it needs to be reduced. This subtopic explores the methods to increase or reduce friction and the importance of these methods in various real-life scenarios.

Increasing Friction

In certain situations, friction needs to be increased to ensure better grip, control, or stability. The following methods are used to increase friction:

• Making the surfaces rough: Rough surfaces increase the interlocking between the irregularities of the two surfaces, which increases friction. For example, the soles of shoes are made rough to provide better grip.
• Increasing the force pressing the surfaces together: By applying more force or weight on the two surfaces in contact, the friction between them increases. For example, applying more pressure on the brake pads of a vehicle increases friction with the wheels, helping to stop the vehicle.
• Using sticky materials: Materials like rubber or certain adhesives are used where increased friction is required, such as on the surface of sports shoes or vehicle tires.

Reducing Friction

In many cases, friction is undesirable and needs to be reduced to enhance efficiency or to reduce wear and tear on machines and moving parts. Some methods to reduce friction are:

• Lubrication: Applying lubricants like oil, grease, or graphite between two surfaces reduces the contact between the surfaces, lowering friction. For example, lubricants are used in the engines of vehicles to reduce the friction between moving parts.
• Making the surfaces smooth: Smoother surfaces reduce the amount of interlocking between them, which in turn decreases friction. For example, finely polished surfaces in machinery or the use of smooth bearings reduces friction in machines.
• Using rollers or ball bearings: Instead of sliding, rolling friction is used. Rollers and ball bearings reduce the contact area between surfaces, thus reducing friction. This is commonly used in conveyor belts, wheels of vehicles, and various types of machinery.
• Streamlining: Streamlining is the process of designing objects in a way that reduces air resistance or friction. This is important in vehicles, airplanes, and sports equipment where reducing friction can improve speed and performance.

Formula for Frictional Force

The frictional force $f$ is given by the formula:

$f = \mu N$

Where:

• $\mu$ is the coefficient of friction, a constant depending on the nature of the surfaces in contact,
• $N$ is the normal force, which is the force perpendicular to the surface.

Factors Affecting Friction

The magnitude of friction depends on two primary factors:

• Nature of the surfaces: Rougher surfaces have higher friction, while smoother surfaces have lower friction.
• Normal force: The greater the force pressing the surfaces together, the greater the frictional force.

In real-world applications, both increasing and reducing friction is crucial in different contexts. Understanding how to manipulate friction allows for better control and efficiency in mechanical and daily life scenarios.