Difference Between Static Friction and Kinetic Friction

Introduction

When you try to push a really hefty block, nothing happens. What do you believe is preventing it from moving? The friction force is what overcomes the force you apply. Friction, also known as frictional force or the force of friction, is the force that resists the relative motion or tendency of two surfaces in contact.

Friction is a type of contact force. It has a higher strength for rough and dry surfaces and a lower strength for smooth and moist surfaces. The friction force acts tangentially along with the two bodies' contact. Friction exists in a pair and is caused by surface imperfections.

Static Friction vs Kinetic Friction

The primary distinction between static and kinetic friction is that static friction acts on a body when it is at rest, whereas kinetic friction acts on a body when it is in motion. The value of static friction varies, but the value of kinetic friction remains constant.

Difference Between Static Friction and Kinetic Friction in Tabular Form

Parameters of Comparison	Static Friction	Kinetic Friction
Definition	The force of friction that acts between two moving surfaces is referred to as static friction.	The force of friction that acts between two moving surfaces is referred to as kinetic friction.
Magnitude	Static friction is a variable force with magnitudes ranging from zero to one. The limiting friction is the greatest value of static friction.	Kinetic friction is a constant force with a smaller magnitude than limiting friction. Its size cannot be 0.
Formula	Because it is a variable force, its formula is not fixed, however the limiting friction formula is as follows: Limiting friction = static friction coefficient Normal force	The kinetic friction formula is as follows: Kinetic friction = kinetic friction coefficient Normal force
Comparison of coefficients of friction	The static friction coefficient is always greater than or equal to the kinetic friction coefficient.	The kinetic friction coefficient is less than or equal to the static friction coefficient.
Examples	A man pushing a stationary heavy block. A young youngster lying over a stationary trolley.	A rolling ball on a table. a person ice skating

What is Static Friction?

The friction or force acting on motionless objects is referred to as static friction. Static friction is defined as the force operating on a stationary object to keep it from moving. It is a self-adjusting force. The limiting friction spans from zero to the maximum static friction force. Limiting friction is the frictional force applied right before the body moves. It has the following formula:

fl = μs × N where,

1. fl is the limiting friction
2. μs is the coefficient of static friction and
3. N is the normal reaction force.

When an external force is applied to a body, the static friction value initially equals the external force applied and increases as the external force increases. The body is on the verge of moving when the external force equals the limiting frictional force. When the external force exceeds the limiting friction, the body begins to move.

A force opposes the motion of any solids or liquid layers. This force is created when two materials slide over one another. Friction can be found all around us. For example, as we walk, our feet make touch with the ground. When we walk, the backward movement of our feet creates a force on the ground while the forward foot travels.

When we exert this force on the ground, the ground exerts an equal and opposite force on our feet. This is consistent with one of the laws of motion. Because of the presence of friction, we can come to a complete halt while running over steep terrain. One thing to remember about friction is that it always acts in the opposite direction of the relative motion, resulting in help in slowing down and eventually halting.

Some of the Major Types of Friction Which are Classified.

• Static friction
• Sliding friction
• Rolling friction
• Fluid friction
• Dry friction
• Skin friction
• Internal friction
• Lubricated friction

Liquid friction: this type of friction is also known as fluid friction. It occurs when viscous liquids come into touch with one another.

Fluid Friction

Fluid friction is the friction that arises between the multiple layers or films of a liquid. This sort of friction typically occurs between the layers of a viscous fluid or between two viscous fluids.

Lubricated Friction

We know that lubricants, mainly oil, are used in many machines to reduce wear and tear on machine parts. Lubricated friction is the frictional force that occurs between this lubricant and the two surfaces of any solid. Lubricated products are used in many devices to reduce friction.

Skin Friction

When a liquid flows across the surface of a solid, a frictional force exists between the liquid and the solid surface. Skin friction is the name given to this form of friction. It is also known as a 'drag.'

Internal Friction

It occurs not just between two solid surfaces, but also between the surfaces' internal components. These are the elements that serve as the foundation for the surfaces. This is why it is often referred to as internal friction.

Frictional force exists not only between external surfaces, but also among the elements that make up a substance. A solid, for example, is made up of elements. Friction between elements occurs when the configuration of a substance, or solid in this case, is modified from its previous configuration. In other words, it occurs when the body suffers deformation.

Dry Friction

Dry friction is the frictional force that occurs when two solid surfaces make contact. This form of friction can be divided into two categories. Kinetic friction and static friction are the two types. When two strong substrates interact, dry friction occurs.

Kinetic Friction

Kinetic friction is the dry friction between two moving surfaces that are sliding over or rubbing against each other. Kinetic friction can also be referred to as sliding friction or dynamic friction.

Kinetic friction occurs when two moving surfaces or solid objects rub or slide against each other. This is also known as dry friction. When the surfaces or substances are not moving, or are static, and the friction between them is static friction. The Kinetic frictional force is activated as soon as something begins to move.

Static Friction

Friction is absolutely everywhere. Static friction is described as a force that resists an object's movement along a path. Finally, visualize it with a simple example. Consider the movement we all do on a daily basis: walking. We are always in contact with the floor while working.

When we move it backward, the motion puts pressure on the floor, which causes us to shift our feet forward. If one wants to prevent friction, one must first understand one fundamental factor: friction operates in the opposite direction of relative motion. This phenomena can be used to slow down and eventually stop the action.

What is Kinetic Friction?

Kinetic friction is the force of friction applied to a body while it is moving. It is an ever-present force. Kinetic friction is the opposition of two objects' relative motion. It always works in the opposite direction of the applied external force.

The kinetic friction can never be greater than the limiting friction. The kinetic friction formula is as follows:

fk = μk × N where,

1. fk is the kinetic friction
2. μk is the coefficient of kinetic friction and
3. N is the normal reaction force

Kinetic friction is also known as sliding friction or dynamic friction. The coefficient of kinetic friction, denoted by k, is often less than the coefficient of static friction, denoted by s. New models are beginning to suggest that kinetic friction can be bigger than static friction, but what we are currently studying is that kinetic friction is always less than the limiting friction, which is static friction's topmost limit.

Kinetic friction is a force that exists between moving surfaces. A moving body on the surface is subjected to a force in the opposite direction of its movement. The size of the force is determined by the kinetic friction coefficient of the two materials.

Friction is simply the force that holds a sliding object back. Kinetic friction is a natural phenomenon that interferes with the mobility of two or more objects. The force acts in the opposite direction of the object's desire to slide.

When we need to stop a car, we need brakes, which is where friction comes into play. When walking and wanting to come to a complete stop, friction is to be thanked once more. But when we have to halt in the middle of a puddle, things get more difficult because friction is reduced and cannot help as much.

Overcoming static friction between two surfaces reduces both the molecular (cold welding between asperities) and, to a lesser extent, the mechanical (interference between the asperities and valleys of the surfaces) obstacles to movement. Once movement begins, some abrasion occurs, but at a considerably lower degree than during static friction, and the relative velocity between the surfaces allows for insufficient time for additional cold welding to occur (except in the case of extremely low velocity).

With the majority of the adhesion and abrasion eliminated, the resistance to motion between the surfaces is reduced, and the surfaces are now moving under the influence of kinetic friction, which is substantially lower than static friction.

Laws of Kinetic Friction

There are four laws of kinetic friction:

1. First law: The force of kinetic friction (Fk) between two surfaces in contact is directly proportional to the normal reaction (N). Where k is a constant known as the coefficient of kinetic friction.
2. Second law: Kinetic friction forces are independent of the shape and apparent area of the surfaces in contact.
3. Third law: It is determined by the nature and material of the surface in question.
4. Fourth law: It is unaffected by the velocity of the object in touch as long as the relative velocity between the object and the surface is not too great.

Equation for Kinetic Friction

An equation is the best way to describe friction force. The friction force is determined by the friction coefficient for the kind of friction being considered, as well as the amount of the normal force exerted on the item by the surface. The frictional force for sliding friction is given by:

Fk = μkFn

F n is the normal force, equal to the object's weight if the issue includes a horizontal surface and no additional vertical forces are present (i.e., F n = mg, where m is the object's mass and g is the acceleration due to gravity). The newton is the unit of frictional force since it is a force (N). The kinetic friction coefficient is not unitary.

The static friction equation is nearly identical to the sliding friction equation, with the exception that the sliding friction coefficient ( s) is substituted with the static friction coefficient ( s). This is best thought of as a maximum value since it increases up to a point and then begins to move if you apply more force to the object:

Fs ≤ μsFn

Main Differences Between Static Friction and Kinetic Friction in Points

1. Static friction keeps a body at rest, whereas kinetic friction slows a moving item.
2. The force of static friction varies, but the force of kinetic friction is constant. Furthermore, static friction is a force that may be adjusted.
3. While static friction can be zero, kinetic friction can never be.
4. The magnitude of static friction ranges from zero to limiting friction, whereas kinetic friction is constant and smaller than limiting friction.
5. Static friction increases with increasing force applied up to a limit, whereas kinetic friction is constant, yet both are directly proportional to normal force.

Conclusion

We just cannot comprehend how the world would have been without frictional force. The frictional force generated by the earth allows us to walk. We couldn't even grip things if frictional force didn't exist.

Static friction is the force that holds a body at rest and its magnitude varies with the change in the external force up to a certain limit, whereas kinetic friction is the force that slows a moving object and its magnitude is constant. When two bodies in touch are at rest relative to each other, static friction occurs, whereas kinetic friction occurs when the two bodies in contact are in motion relative to each other.