The phenomenon of friction in human life plays both a positive and a negative role. On the one hand, without its presence, movement would be impossible, on the other hand, due to friction, huge losses of energy and working materials occur. In the article, we will consider from the point of view of physics what friction is, as well as how to find the coefficient of friction.
Friction phenomenon
Friction is a contact phenomenon that occurs in the zone of contact between different bodies, and which counteracts any of their mutual movement.
In the mechanics of motion of solids, three types of friction are distinguished:
- acting at rest;
- acting while sliding surfaces over each other;
- caused by rolling bodies.
Standing friction occurs when we apply an external tangential force to a surface on a body to move it. A striking example of sliding friction is the sliding of skis on snow. Finally, friction during rollingmanifests itself when the wheel of the vehicle is rolling on the road.
Formula for determining the force of friction
In physics, the listed types of friction are described by the same formula when calculating the acting forces. This formula looks like this:
Ft=µN.
The friction force Ft is equal to the product of the friction coefficient µ and the support reaction N. When considering the corresponding type of friction, only the value of the coefficient µ, which is a dimensionless quantity, changes.
In the case of static and sliding friction forces, the value of µ is about tenths of a unit. µ depends on the contacting materials, on their surface roughness, and does not depend on the contact area or sliding speed.
For rolling friction, the coefficient µ (it is usually denoted CR) depends on the elasticity characteristics of the rolling body, on its hardness, on the rolling radius and some other factors. For most materials, this rolling factor is in hundredths and thousandths of unity.
Since there are many factors affecting the value of µ, there is no definite mathematical formula for its calculation. Answering the question of how to find the friction coefficient, it should be said that it is measured experimentally.
Determining the coefficient µ
In this paragraph, we will consider two ways of practical determination of the value of µ using the example of sliding and rest friction.
The first way to answer the question of how to find the coefficient of friction,consists in placing a bar on a horizontal plane, to which a dynamometer is attached. The bar and the plane are made of the investigated pair of materials, for example, glass and wood. By moving the bar evenly, holding the dynamometer, you can determine the sliding force Ft. Knowing the mass m of the bar, the coefficient µ is calculated as follows:
µ=Ft / (mg).
The second method is convenient for determining µ for static friction. To do this, you need to place a bar on a horizontal plane. Then, one end of the plane should be slowly raised, tilting it at a certain angle to the horizon. At a certain angle θ, the bar will begin to slide off the surface. By measuring this angle, the coefficient of friction µ can be determined from the equation:
µ=tg(θ).
Measuring µ for rolling friction involves using a more sophisticated setup called an inclined pendulum. The calculation of µ in this case is performed by studying the equations of motion dynamics.
