How to find the coefficient of friction: experimental methods

2024 Author: Angel Austin | [email protected]. Last modified: 2024-01-02 17:39

Friction is the physical process without which the very movement in our world could not exist. In physics, to calculate the absolute value of the friction force, it is necessary to know a special coefficient for the rubbing surfaces under consideration. How to find friction coefficient? This article will answer this question.

Friction in physics

Before answering the question of how to find the coefficient of friction, it is necessary to consider what friction is and what force it is characterized by.

In physics, there are three types of this process that occurs between solid objects. This is the friction of rest, sliding and rolling. Friction always occurs when an external force tries to move an object. Sliding friction, as the name suggests, occurs when one surface slides over another. Finally, rolling friction occurs when a round object (wheel, ball) rolls on some surface.

What all types have in common is the fact that they prevent anyonemovement and the point of application of their forces is in the area of contact between the surfaces of two objects. Also, all these types convert mechanical energy into heat.

The forces of sliding and static friction are caused by microscopic roughness on surfaces that rub. In addition, these types are due to dipole-dipole and other types of interactions between atoms and molecules that form rubbing bodies.

The cause of rolling friction is related to the hysteresis of elastic deformation that appears at the point of contact between the rolling object and the surface.

Friction force and coefficient of friction

All three types of solid friction forces are described by expressions that have the same form. Here's her:

F_t=µ_tN.

Here N is the force acting perpendicular to the surface on the body. It's called the support reaction. The value µ_{t- is called the coefficient of the corresponding type of friction.}

Coefficients for sliding and rest friction are dimensionless quantities. This can be understood by looking at the equality of the friction force and friction coefficient. The left side of the equation is expressed in Newtons, the right side is also expressed in Newtons, because N is a force.

As for rolling friction, the coefficient for it will also be a dimensionless value, however, it is defined as the ratio of the linear characteristic of elastic deformation to the radius of the rolling object.

It should be said that the typical values of the coefficients of sliding and rest friction are tenths of a unit. For frictionrolling, this coefficient corresponds to hundredths and thousandths of a unit.

How to find the coefficient of friction?

Coefficient µ_{tdepends on a number of factors that are difficult to take into account mathematically. We list some of them:}

• material of rubbing surfaces;
• surface quality;
• the presence of dirt, water and so on on it;
• surface temperatures.

Therefore, there is no formula for µ_t, and it has to be measured experimentally. To understand how to find the coefficient of friction, it should be expressed from the formula for F_{t. We have:}

µ_t =F_t/N.

It turns out that to know µ_{t it is necessary to find friction force and support reaction.}

The corresponding experiment is performed as follows:

1. Take a body and a plane, for example, made of wood.
2. Cling the dynamometer to the body and evenly move it over the surface.

At the same time, the dynamometer shows some force, which is equal to F_{t. The ground reaction is equal to the weight of the body on a horizontal surface.}

The described method allows you to understand what the coefficient of static and sliding friction is. Similarly, you can experimentally determine µ_trolling.

Another experimental method for determining µ_{t is given in the form of a problem in the next paragraph.}

Problem to calculate µt

The wooden beam is on the glass surface. By smoothly tilting the surface, we found that the sliding of the beam begins at an angle of inclination of 15o. What is the coefficient of static friction for a wood-glass pair?

When the beam was on an inclined plane at 15o, then the rest friction force for it had a maximum value. It is equal to:

F_t=mgsin(α).

Force N is determined by the formula:

N=mgcos(α).

Applying the formula for µ_{t, we get:}

µ_t=F_{t/N=mgsin(α)/(mgcos(α))=tg(α).}

Substituting the angle α, we arrive at the answer: µ_{t=0, 27.}