# Advice 1: How to find the braking force

Power braking is the force of sliding friction. If the force applied to the body exceeds the maximum force of friction, the body begins to move. The force of sliding friction always acts in a direction opposite to the velocity.
Instruction
1
In order to calculate the force of sliding friction (Fтр), you need to know the time of braking and stopping distance.
2
If you know the time of braking, but not known for its braking distance, you can calculate by the formula:s = υ0⋅t/2, where s is the stopping distance, t – time braking, υ0 is the velocity of the body at the beginning of braking.To calculate the speed of the body at the beginning of the braking you'll need to know the braking distance and time of braking. Calculate it by the formula:υ0 = 2s/t, where υ0 is the velocity of the body at the beginning of braking, s – stopping distance, t – time braking.
3
Note that the stopping distance is proportional to the square of the initial speed before braking and inversely proportional to the magnitude of the force of sliding friction (power braking). That is why, for example, on dry roads (when calculating for cars) shorter braking distance than slippery.
4
Once you become aware of all the values, substitute them in the formula: Fтр = 2m⋅s/t2, where FTR silyl sliding friction (power braking), m is the mass of a moving body, s is the braking distance, t – time braking.
5
Knowing the power of braking, but not knowing his time, you can make the necessary calculations according to the formula:t = m⋅υ0/ Fтр, where t is the time of braking, m is the mass of the moving body, υ0 is the velocity of the body at the beginning of braking, FTR silyl braking.
6
Calculate the force of sliding friction according to another equation:Fтр = μ⋅ Fнорм where FTR silyl sliding friction (power braking), μ – coefficient of friction, Fнорм – force of normal pressure of the pressing body to the support (or mg).
7
Determine the coefficient of friction experimentally. In school textbooks in physics it is usually already indicated in the conditions of the problem, if you do not want to calculate it for some particular body during laboratory work. To do this, place the body on an inclined plane. Determine the angle at which the body starts moving, and then find out the tables or independently calculate the tangent values of the angle α (the ratio of opposite over adjacent). This will be the value of the coefficient of friction (μ = tg α).

# Advice 2: How to find frictional force

Friction – the process of interaction of two bodies, causing deceleration at offset relative to each other. Find force friction means to determine the magnitude of the impact is directed in the direction opposite to the movement, because of which the body loses energy and eventually stops.
Instruction
1
The force of friction is a vector quantity, which depends on many factors: the pressure of bodies upon each other, the materials from which they were made, speed. Surface area in this case is irrelevant, because the bigger it is, the more reciprocal pressure (reaction force bearing N), which is already involved in finding the force of friction.
2
These quantities are proportional to each other and connected with a coefficient of friction μ, which can be considered constant, if greater accuracy of calculations is not required. So to find the force of friction, you need to calculate the product:Fтр = μ•N.
3
Given the physical formula refers to the friction caused by sliding. It can be dry and wet, if between the bodies is present in the liquid layer. The force of friction must always be taken into account in determining the totality of the forces acting on the body in solving problems.
4
Rolling friction occurs during rotation of a body on the surface of another. It is present on the boundary of contact bodies that is constantly changing. However, the force of friction constantly opposes the motion. On this basis, it is equal to the ratio of the product of the coefficient of friction of the rolling and pressing forces to the radius of a rotating body:Fтркач = f•N/r.
5
We must distinguish between the coefficient of friction of sliding and rolling. In the first case is the value with no dimension, in the second it represents the distance between the straight lines that characterize the direction of clamping forces and the reaction forces of the supports. Therefore, it is measured in mm.
6
The coefficient of friction of rolling is usually a known value for common materials. For example, for iron for iron it is equal to 0.51 mm for iron on wood – 5,6, wood on wood – 0,8-1,5, etc. it can be Found by the formula the ratio of the moment of friction by the pressing force.
7
The force of friction of rest you receive at the minimum displacement or deformation. This force is always present in the dry slide. Its maximum value equals μ•N. There is also internal friction within the body between its layers or parts.
Note
Uniform motion of a body is characterized by the balance between the external force and the frictional force.
Search