What is the force of friction? Any idea! In this article, we will learn the basics of friction, definition, equations or formula, types, along with examples.
As you look around you there are many forces at play doing their own jobs in their respective fields
Take an example of a truck driver driving a truck, when a speed breaker approaches you to hear loud noises and the truck tends to get stopped as he applies the brake.
That you must be wondering. Well, friction force acts opposite to regular motion, and it retards the movement of the moving object.
Let take an example of a bicycle where small disc brake help you stop it there also similar force is applied. These are the examples when braking force was applied but what about the places where it is not applied and still the motion of the object comes to standstill.
This does not involve friction force but as soon as it is moved tangentially over one another force of friction acts and its interlocking property opposes the movement and inhibits the motion.
This opposing force, which operates in the opposite direction of the upper block’s movement, is known as the force of friction or simply friction.
As a result, at every joint in a machine, friction is caused by the relative motion of two components, and therefore some energy is spent in overcoming the friction.
Though friction is regarded as undesirable, it plays a significant part in both nature and engineering, for example,
For the automobile to go ahead, friction between the wheels and the road is required.
The frictional force can be easily calculated from the definition,
F= μ N
Hence, Normal force, N,
Hence, considering this weight, the force of friction formula can be written as,
F= μ mg
Now, if the surface is inclined and if it makes an angle θ, then
Hence, considering this angle, the force of friction formula can be written as,
F= μ mg cosθ
As the frictional force is one type of force, the unit of frictional force will be the same as force.
It is defined as the ratio of the limiting friction (F) between two bodies to their normal response (N). It is generally denoted by μ.
Mathematically, coefficient of friction,
μ = F/N
Its value is different for different materials. As the coefficient of friction is the ratio of two different forces, it will be unitless. For metal between 0.15 to 0.60 while stone 0.40 to 0.70.
We have got the basic equation for frictional force. It is F= μ Rn. Hence, if we know, Rn and μ, it will be easy to find out the force of friction!
Let’s see, how to calculate the frictional force in simple steps?
Step-1: Calculate Normal Force
When an object is kept on a surface, the weight of the object is acting vertically down.
The object is stable and the surface is horizontal in our example. Hence, the normal force will act on the surface vertically upwards to balance the weight, which is acting vertically down.
Hence, Normal force, N,
Now, if the surface is inclined and if it makes an angle θ, then
Step-2: Finding the Value of Coefficient of Friction
The coefficient of friction depends on the type of materials, surface roughness, etc.
In this way, we will get the value of μ.
Step-3: Calculate the Force of Friction
So, we have got the value of N and μ.
Now, to get the frictional force, F
Let’s see a simple example to understand the frictional force.
A copper block of 5kg mass kept on a horizontal cast-iron surface. The copper block is at rest and the frictional factor acts between the copper block and the cast-iron surface is 1.05.
Find out the frictional force.
Hence, frictional force, F
It is the friction that is experienced by a body when it is at rest.
It is the friction force experienced by a body when it is moving that is in motion. Dynamic friction is also known by the name kinetic friction and always less than that of static friction.
It has three types
The friction may further be classified as:
Boundary friction (also known as greasy friction or non-viscous friction)
Fluid friction (also known as film friction or viscous friction)
What is viscosity?
What is oiliness?
1. The frictional force will always acts in a direction exactly opposite to the direction of applied force.
2. The magnitude of the force of friction is exactly equal to the applied force which causes body to move.
3. The magnitude of the limiting friction (F) forms a constant ratio to the normal reaction (N) between the two surfaces.
F/N = constant
4. The force of friction is not dependent of the area of contact, between the two surfaces.
5. The force of friction depends upon the roughness of the surfaces in between.
1. The frictional force will always act in a direction exactly opposite to the direction of applied force.
2. The magnitude of kinetic friction is proportional to the normal response between the two surfaces. However, this ratio is slightly lower than in the case of limited friction.
3. The force of friction remains constant at modest speeds. However, it continues to drop somewhat as the speed increases.
1. The friction force is proportional to the normal load between the surfaces.
2. For a given normal load, the force of friction is independent of the area of the contact surface.
3. The friction force is determined by the material of the contact surfaces.
4. The force of friction is independent of the velocity at which one body slides relative to the other.
1. The frictional force is virtually completely independent of the load.
2. The force of friction decreases as the temperature of the lubricant rises.
3. The friction force is unaffected by the materials of the bearing surfaces.
4. The frictional force varies depending on the lubricant.
Consider a body A on the surface of body B. the applied force P is applied over it while force F is the frictional force that resists its movement as it acts in its opposite direction.
Where Rn is a normal reaction. Under the influence of three forces, the body will be in equilibrium.
As a result, the reaction R must be equal to and opposite to the product of W and P, as well as inclined at an angle to the normal reaction N. This angle is known as the frictional restriction angle.
It is defined as the angle formed by the resulting reaction R with the normal reaction N.
tan φ = F/N = μ N/ N = μ
Significance of this angle is that the effort P will be minimum if its inclination with the horizontal is equal to the angle of friction.
The main function of the clutch is the transmission of power from a prime mover to a shaft. It is placed in between the shaft and prime mover and is needed as machines must start and stopped during loading and unloading.
The load also keeps changing. So instead of always switching on or off the prime mover clutch is used.
While in case of automobiles to change gears fluently without jerk it becomes necessary to disengage the power drive. This device gradually brings up the speed.
Its working principle is – when two rotating discs of high roughness when touch each other transfer the power and when they are away transmission is stopped.
Depending on its use clutches are of various types:
It is a device that is used to stop automobiles or retard after an increased acceleration. Basically, it reduces the speed, this is done by using friction force which is applied by the braking pads on a rotating wheel.
Its designing principle is simple.
The highly rough and abrasive material is used as a braking pad which gets rubbed on a wheel drum or brake plate.
Depending on their construction it has 2 types.
It is branch of engineering which deals with the designing of shapes in such a way that friction on body gets reduced.
Even air offers resistance to a moving body when it travels at high speed thus to reduce this friction aerodynamic shape is given to the vehicle.
The design of high-speed trains, sports cars, and aeroplanes are a common example in which designing a body with reduced frictional force is important.
To keep friction minimum whilst transferring power by maintaining either point or line contact.
A friction bearing is made up of a permanent, non-moving bearing surface, such as machined metal or a pressed-in bushing, that serves as a low-friction support surface for rotating or sliding surfaces.
Lubricating oil is often used in friction bearings to separate the moving component from the mated non-moving bearing surface.
|Desirable Friction||Undesirable Friction|
|This leads to loss of energy but that’s the end goal. Ex breaking vehicle||It leads to loss of energy but that’s not end goal. Ex propulsion of aircrafts, missiles.|
|It leads to wear and tear of object, but here done to remove material. Ex grinding machine||It leads to wear tear of object. Ex machines gears|
|Designing principle for specific gadgets. Ex clutch, brake||It is avoided by use of other substance. Ex lubricant, grease|
A 50 kg metal object on a horizontal desk is pushed by a horizontal force
of 246 N. The frictional factor is 0.5.
Determine whether the metal object will move or not.
From the question, we can write the given data,
What to prove?
We need to check whether the metal object will move or not.
The metal object is kept on a horizontal surface, and obviously, the frictional force is acting between the object and the surface.
Now, there may be two options,
Calculation & Proof
First we will calculate, the frictional force, F
F = μ N
F = 0.5 x 50 x 9.8
F = 245 N
This is the less than the applied horizontal forc, Fh=246 N.
F < Fh
Hence, the metal object will move.
Hence, we have got an idea about frictional force. Any questions, please let us know.
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