Have you ever wondered why a cycle stops if we do not peddle? There must be something acting upon it. That something is actually a force. It is called frictional force. We can define friction in physics as an opposing force between two bodies in relative motion.
Friction enables us to walk, climb, etc., but it also makes us waste a lot of energy in the process, and that’s why we get tired. Friction is a necessary evil. In this article, we try to define friction, look at the causes of friction, the formula for friction, types of friction, and some real-life examples of friction.
Definition of friction force
1. Friction is a force that opposes relative motion between 2 bodies in contact.
2. It acts in the opposite direction to the force applied and parallel to the surface.
3. The friction force depends on the type of material sliding.
4. It may arise due to the roughness of surfaces or even attraction between molecules of the two sliding surfaces.
According to Newton’s first law of motion: A body is in uniform motion in a straight line while remaining in motion unless and until acted upon by an external opposing force.
That means, there is an external force that is stopping the ball. This force seems to be invisible. This is the force of friction.
What is the cause of friction?
Frictional force arises due to the roughness of surfaces. At the microscopic level, we find many irregularities on both surfaces. The above image explains how a frictional force is set up at the microscopic level. It is very difficult to find ideally smooth surfaces. You can read more about the factors that contribute to friction here.
How to measure friction in real life?
Friction is based on the general formula F = μN, where μ is the coefficient of friction. If you know the coefficient of friction of a surface then you can easily find the value of friction. Generally, the normal force is the weight of the object given by mg. Where m is the mass of the object and g is the acceleration due to gravity.
In most cases, the coefficient of friction is not known exactly. Then we require devices to measure the coefficient of friction. It can also be measured using some simple principles of physics, like the spring balance or the pendulum method.
Quiz
Image by Oleksandr Pyrohov from Pixabay
What is the direction of the frictional force?
Frictional force always acts in a direction opposite to the motion of the sliding object and parallel to the sliding interface. The below image explains how the ball in motion comes to a halt due to the force of friction.
Examples of friction in our daily lives
When we walk on wet surfaces, we tend to slip and fall. Have you wondered why? It is because liquids like water decrease the friction of the surface, and hence we lose grip on the surface and fall down.
It is very difficult to find a perfectly smooth surface. But in an ideal case of a smooth surface, there will be no friction. The animation below demonstrates how a frictionless surface will behave.
The force of friction comes into play only when the two surfaces are sliding over each other. The below animation shows a case of action-reaction where a ball strikes against a wall, but there is not much sliding. This is not an ideal example of friction.
Why do we rub our hands together in winter? When we rub our hands together the friction between our hangs generates a certain amount of heat which is enough to keep us warm during winter times.
When two surfaces are sliding over each other there is always a frictional force present. This frictional force gives rise to a small amount of heat. The simulation here explains the heat generation process with the representation of atoms at the sliding interface. Go ahead and slide the blue surface across the green one and see what happens.
Friction is unavoidable in our daily lives. This funny video shows how life would be without friction. You can read our blog on 50 examples of friction in our daily lives to know more. We have listed below the 5 most common examples of friction.
- Walking on a road
- Lighting a matchstick
- A ladder against a wall
- Holding onto objects
- Brakes stopping a car
Heating effect of friction
When two surfaces slide over each other there is a heating effect associated with it. Now, this is a necessary evil. We can use this heating effect of friction to create fire for useful purposes like lighting a matchstick. But, on the other hand, friction can also create unwanted fires like forest fires. This comic video explains friction as a necessary evil in a funny way. You can also learn more in this interactive simulation explaining the heating effect of friction.
Formula of friction
f = μ*N, where N is the normal force and μ is the coefficient of friction.
How can we calculate the normal force?
For an object in motion on the x-axis, the net normal force is zero. The weight of an object mg acts in the normal direction and the normal force acts in the upward direction. So, N = mg is the general case, unless acted upon by any external force in the y-axis or if the object is at an incline.
What are the types of friction?
Friction can be classified based on the motion of the object, state of matter, and mode of contact established. You can read more about the types of friction here.
- Rolling friction
- Sliding friction
- Kinetic friction
- Static friction
- Dry friction
- Fluid friction
- Air resistance
- Quantum friction
- Pipe friction
What is tribology?
The study of friction and its related phenomena is commonly called tribology. Friction was first discovered by Leonardo da Vinci and he is the first known tribologist.
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Research on Friction
AZ91 alloy is a material with excellent strength, corrosion resistance, and good cast-ability. It is used in many die-casting projects. In this article, the authors have studied the frictional properties of the material and also ways of reducing friction. The influence of additives like (Praseodymium) Pr addition and heat treatment on the dry sliding wear behavior for AZ91 alloy is studied. The authors used a pin-on-disc tribometer to measure wear rates and friction coefficients. [Link:https://doi.org/10.3390/cryst8060256]
The LDPE[low-density polyethylene] composites with glass particles have been widely used for low-friction applications. Read this paper to find out how the authors have used this LDPE composite for low-duty friction applications using 3D printing. [link:https://doi.org/10.3390/ma12162520]
For vehicle active braking control systems such as ABS, ASR, or ESP road friction information is very important. Because of the nonlinear system, parameter uncertainties, and signal noises, it is very difficult to estimate the tire-road friction forces and coefficient accurately. Read this paper on how authors have worked on the development and verification of the tire/road friction estimation algorithm for the antilock braking system. [Link:https://doi.org/10.1155/2014/786492]
See also
- Factors affecting friction
- Friction is a necessary evil
- What are the applications of friction in our daily lives?
- How can we increase friction? What are the ways of doing it?
- How can we decrease friction? What are the ways of doing it?
- Quiz on friction
- What is rolling friction?
- What is fluid friction?
- What is static friction?
- 50 Examples of friction in our daily lives
