Frictional Force Material: Definition, Types, Formulas, Examples

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Friction is a type of physics that is widely applied in everyday life. Force can be interpreted as an interaction that when working can cause changes in conditions or motion of objects. Force is affected by a push or a pull.

Force is related to Newton's Laws so the derived SI unit for force is defined by the symbol N. Any type of interaction can cause an object that has mass to change its motion. The force against friction is divided into two types, namely static and kinetic.

List of contents

Definition of Friction

Definition of Friction

Friction is a type of force that is often encountered in everyday life. This force will arise because of the touch between the plane and the object. Friction that occurs will cause movement of objects.

The amount of friction produced can be determined from the texture of the two surfaces that are in contact with each other. If the surface is rough, then the friction that occurs will be greater. If it is smooth then the friction is getting smaller.

This happens because the surface will inhibit or smoothen the friction of the tangent planes. Rough surfaces can make objects become blocked making it difficult to move.

On a slippery surface, objects move faster and the amount of friction that occurs is smaller. The harder an object to move, the greater the friction will be. Friction prevents objects from moving.

Friction always has a direction that is opposite to the direction of motion, meaning that it is opposite to the direction of motion of an object. If a ball moves to the right, friction is to the left. For example, when a car is parked, the thrust is to the right, the friction is to the left.

If defined simply, friction occurs due to two surfaces of objects that meet each other. The friction that occurs on the objects in contact has a value that is not the same. The magnitude of the friction value can be caused by certain factors.

Read: Newton's Laws 1, 2, 3

Static Friction Formula

Static Friction Formula

This type of friction works when the surfaces that meet do not slide over each other. It can be interpreted that this force acts on an object that is given an external force (F) such as a pulling or pushing force to an initial object that is at rest until it will move.

This type of static friction occurs between two solid objects that are not moving relative to each other. This force occurs when an object slides down an inclined plane. Here's the calculation formula.

fs = s x N

Explanation:

fs: amount of static friction (N)

s: coefficient of static friction (N)

N: normal force (N)

Kinetic Friction Formula

Kinetic Friction Formula

Kinetic friction is also known as dynamic. This force will occur when two objects that are moving relative to each other rub against each other.

The coefficient of kinetic friction is usually always smaller than that of static friction even though it occurs in the same material. Kinetic friction acts on objects that are in motion. Check out the following calculation formula.

fk = k x N

Explanation:

fk: magnitude of kinetic friction (N)

k: coefficient of kinetic friction (N)

N: normal force (N)

Read: Power Formula

How to Determine the Rest of an Object's Motion

How to Determine the Rest of an Object's Motion

After understanding the formula for kinetic and static friction, the next thing to understand is knowing whether an object is at rest or in motion. To determine this, you can compare the static frictional force on an object with the external force (F). Here's the information.

  • If the external force compared to static friction is the same, it means that the object will move (F = fs).
  • If the external force compared to static friction is smaller, it can be concluded that the object is at rest (F < fs).
  • If the external force is greater than static friction, it means that the object is moving (F > fs).

Example of Application of Friction Force

Example of Application of Friction Force

Friction is one of the most common styles, even closely related to daily activities. Check out some examples of its application below.

  • When the vehicle is moving, there will be friction between the asphalt and the wheels.
  • When erasing or writing, there will be friction between the pen or eraser and the paper.
  • When rubbing the palms of the hands to warm the body, there will be friction between the hands.
  • When running, there is friction between the ground and the feet.
  • When pushing a chair, there will be friction between the floor and the chair.
  • When pushing the table on a rough surface, the greater the friction generated. Whereas on a smooth surface or a table with wheels, the friction that occurs will be smaller.
  • When you're mopping, there will be friction between the mop and the floor.

Read: Gravity

Sample Questions and Discussion

Sample Questions and Discussion

In order to better understand the discussion of friction, it takes questions to hone skills. That way the calculation of the magnitude of the force generated can be calculated properly. Check out some examples of the questions below.

Example 1:

On a rough surface there is a block with a mass of 10 kg. If it is known that the static friction s = 0.4 and the coefficient of kinetic friction k = 0.3, what is the friction of the block if it is pulled using a force of 20 N?

Discussion:

Is known:

m = 10 kg

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s = 0.4

k = 0.3

F = 20 N

Asked: f

Answer:

The first way is the normal force first.

FY = 0

N – w = 0

N = w

N = mg

N = (10) (10)

N = 100 N

After that find the static friction.

fs = s x N

fs = 0.4 x 100

fs = 40 N

It is concluded that F < fs means the block is still at rest. It can be calculated by Newton's first law as follows.

F = 0

F – f = 0

F = f

f = 20 N

So it can be concluded that the amount of friction acting on the block is 20 N.

Example 2

A block weighing 25 kg is on a rough floor. It is known that s = 0.7 and k = 0.3. The block is given a tensile force of 160 N horizontally. Calculate the amount of friction experienced by the block.

Discussion:

Is known:

m = 25 kg

s = 0.7

k = 0.3

F = 160 N

Asked: f

Answer:

The first step is to find the magnitude of the normal force (N):

FY = 0

N – w = 0

N = w

N = mg

N = (25) (10)

N = 250 N

Look for static swipe first:

fs = s x N

fs = 0.7 x 250

fs = 175 N

Since F > fs, the block is in a moving position. For that, find the following magnitude of kinetic friction.

fk = k x N

fk = (0.3) (250)

fk = 75 N

It is concluded that the friction experienced by the block is 75 N.

Kinetic and static friction have different criteria and calculations. By understanding how to calculate it, working on practice questions can be done more easily and quickly. This certainly can improve understanding of the material.

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