Ever wonder why it’s so hard to slide a heavy box across the floor? Or why you slow down when riding a bike? The answer is friction. Friction both helps and hinders us in our daily lives. As much as you may curse it when dragging furniture across the room, friction is actually pretty useful. Without it, you wouldn’t be able to walk, drive a car, or pick up objects.
In this article, we will go through the meaning, types, laws, and the advantages and disadvantages of friction.
What Is Friction?
Friction is the resistance that opposes the relative motion of two surfaces in contact. In short, it’s what stops things from sliding smoothly over each other. For example, when you try to push a heavy box across the floor, friction works against you. But without friction, walking would be nearly impossible. Your feet would slip and slide with every step.
Friction also produces heat through the vibration of atoms. Rub your hands together vigorously, and you’ll feel warmth generated from friction. This is why spacecraft heat up when re-entering Earth’s atmosphere. While friction can be inconvenient, it’s essential for many everyday tasks. Pens and pencils wouldn’t work without friction between the writing tip and the paper. And friction between your shoes and the ground allows you to accelerate, brake, and change direction.
What are the Causes of Friction?
A frictional force acts between two surfaces and resists the relative motion of the objects containing these surfaces. The main causes of friction can be described by three major reasons in relation to the surface of objects:
- Molecular adhesion
- Surface Roughness
- Deformation
When two materials are brought into proximity, a molecular force known as adhesion acts between them. When the materials are abrasive enough to cause significant abrasion, surface roughness becomes a factor in friction. Deformations or plowing action provide much of the movement resistance when one or more of the materials is relatively soft.
While friction enables us to walk, open doors, and drive cars, reducing friction is useful for applications like sliding and transportation. Understanding the causes of friction helps us control it to our advantage.
Types of Friction
Friction comes in many forms that affect our daily lives in both positive and negative ways.
There are four main types of Friction, namely;
- Static friction
- Limiting friction
- Kinetic or dynamic friction
- Fluid friction
Static Friction
Static friction occurs when two surfaces are at rest relative to each other. It resists the motion of objects and helps keep things in place. Static friction is the opposing force that occurs when one body tends to move along the surface of another, but the actual motion has not yet begun. Static friction is a force that self-adjusts to the applied force and is always equal to the net external force. For example, static friction between your shoes and the floor allows you to walk without slipping.
Limiting friction
The force of friction increases as the applied force increases. When the applied force exceeds a particular threshold, the body begins to move. Limiting friction refers to the maximum value of friction beyond which the body does not move. Limiting friction always works in the opposite direction that the body is about to move over the other.
Kinetic Friction
When the applied force on a body surpasses the limiting friction and causes the body to move, the friction acting on the body in the opposite direction of motion is referred to as kinetic friction.
Kinetic friction is further divided into two categories:
- Sliding Friction
- Rolling friction
Sliding friction
Sliding friction occurs when two solid surfaces slide over each other. It resists the sliding motion of objects and converts mechanical energy into heat. For example, sliding friction between brake pads and rotors slows down a vehicle by converting its kinetic energy into heat.
Rolling Friction
When rolling objects like a disc, ring, wheel, or cylinder roll over a surface, the force resisting the body’s rolling motion on the surface is referred to as rolling friction. The loss of energy necessary for the deformation of the objects in contact causes rolling friction. Rolling friction is always directly proportional to normal response N and inversely proportional to rolling body radius (r).
Fluid friction
Fluid friction is the force that opposes the opposite movement of two fluid layers or the relative motion of the fluid layers. Fluid friction is defined as the viscosity of a fluid that resists the movement of fluid layers relative to each other. In general, viscosity is also referred to as a fluid’s resistance and thickness or thinness.
Water is considered to be thin with the lowest viscosity, implying that the fluid friction between the different layers of water is the least when compared to any highly viscous fluid. Fluid friction acts on an object in the opposite direction if it moves across any layer of the fluid.
Fluid friction occurs when an object moves through a fluid (either liquid or gas). It resists the motion of objects moving through fluids and slows them down. For example, fluid friction between air and a skydiver slows their descent.
Friction affects our world in both positive and negative ways. Understanding the different types of friction and how they work allows us to maximize the benefits and minimize the costs.
Advantages and Disadvantages of Friction
Friction has both positive and negative effects on our daily lives. On the plus side, friction allows us to walk without slipping, drive our vehicles, and hold objects firmly in our hands. However, friction also reduces efficiency and causes wear and tear.
Advantages of Friction
Friction plays an important role in both enabling and hindering motion and contact between objects. Finding the right amount of friction for any given situation is key to maximizing the benefits and minimizing the costs.
Here are the Advantages of Friction:
- It produces heat through resistance to motion. This is useful for starting fires or warming up by rubbing hands together.
- It slows down moving objects, which is important for safety and control. Brakes on vehicles use friction to stop the wheels from turning.
- Friction gives us traction, which is the grip between two surfaces. Without friction, we wouldn’t be able to walk, drive, or do many other everyday tasks.
- Friction between the ground and our shoes allows us to move around without slipping. Similarly, friction between tires and the road enables our vehicles to accelerate, steer, and brake.
- Machines also rely on friction to function properly. Conveyor belts, for example, use friction to transport objects. Many manufacturing processes involve the precise application of friction, like cutting, bending, and shaping materials.
Lack of friction would make the world a slippery and treacherous place. Simple acts like sitting down, grasping objects, and opening doors depend on friction to function properly. Friction is truly essential for mobility and manipulating the physical world around us.
Disadvantages of Friction
While friction enables many useful functions, it also has some downsides, which include:
- It reduces efficiency by transforming useful energy into heat. This results in energy loss. For example, when you rub your hands together quickly, the friction between your hands causes them to warm up. That heat is energy that could have been used to do useful work but was instead lost due to overcoming the friction between your hands. Reducing friction, such as by lubricating surfaces or using ball bearings, allows more of the input energy to be converted into useful work.
- In mechanical systems, friction leads to the wastage of energy through heat and requires extra force to overcome. Minimizing friction, where possible, results in improved performance, less energy usage, reduced heat generation, and lower wear and tear. While some friction is necessary, excess friction should be avoided.
- It causes wear and tear through contact between two surfaces. The rubbing of two surfaces against each other causes gradual damage and deterioration. This results in wear and tear of materials and machine parts.
- It makes motion and transportation more difficult. Heavy friction requires more force and energy to overcome.
- It produces heat. The kinetic energy of moving objects is converted into heat due to friction. This can lead to overheating and damage.
The primary disadvantage of friction is that it reduces efficiency. When two surfaces rub against each other, it requires extra energy and effort to overcome the resistance and move the objects. This wasted energy is transformed into heat, reducing the total amount of useful work that can be done.
What are the Factors Affecting Friction?
The amount of friction depends on several factors:
Surface Area
The larger the surface area of contact between two surfaces, the greater the friction. This is because more surface area means more points of contact and more interlocking between irregularities of surfaces.
Nature of Surfaces
Rough and irregular surfaces provide more friction than smooth surfaces. This is because rough surfaces have more surface area and more points of contact. Smooth surfaces like Teflon provide less friction.
Strength of Intermolecular Forces
Stronger intermolecular forces between molecules of surfaces lead to higher friction. For example, friction between two metals is higher than between a metal and a plastic. This is because metallic bonds in metals are stronger than intermolecular forces in plastics.
Load
The friction increases with an increase in load or applied force. This is because a greater load causes more surface area to come in contact and increases the strength of interlocking between irregularities.
Condition of Surfaces
Dry, clean surfaces provide higher friction than lubricated or greasy surfaces. This is because lubricants like oil and grease fill up the irregularities and reduce the points of contact between the surfaces.
What are the Laws of Friction?
When two surfaces are in contact and moving relative to each other, friction comes into play. Friction opposes the motion of the surfaces and converts kinetic energy into heat. There are five laws of friction to keep in mind:
- Friction is proportional to the normal force exerted between the surfaces.
- Friction does not depend on the area of contact.
- Friction force depends on the type of surfaces in contact.
- The coefficient of static friction is greater than the coefficient of kinetic friction.
- The speed of an object does not change the amount of friction.
Knowing these laws helps in understanding how friction impacts motion and forces. Reducing friction where possible, such as with lubricants, can help improve mechanical efficiency. Understanding friction is key to controlling motion.
Conclusion
So there you have it: friction can be both friend and foe. While it may wear down our tires and the soles of our shoes over time, friction is what allows us to walk, drive, and function in the physical world. Without it, we’d be slipping and sliding all over the place. We’d have no traction or ability to grasp and manipulate objects. Life as we know it wouldn’t be possible. So even though friction causes annoyance and inefficiencies, we should appreciate all the ways, big and small, that it improves our lives and makes the world work. Next time you stub your toe or get a blister, remember it’s a small price to pay for being able to navigate the world.