In order to calculate the force of sliding friction (Fтр), you need to know the time of braking and stopping distance.
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.
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.
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.
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.
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).
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).