Lesson 2: How Rough It Is

The coefficient of friction (µ) is a measure of the roughness of a surface. The larger the value of µ, the rougher the surface. Can you determine which factors affect the value of µ and which have no effect?

Doing the science

1. You must have completed Lesson 1 prior to conducting this lesson. You must have the data from Lesson 1, Table 1 for this lesson’s calculations.
2. Use the following equation to convert the masses (m) (1.0 and 2.0 kilograms) from Lesson 1 into weight, which is the force (f_g) due to gravity (in newtons). Record the forces in Table 1.
   f_g = mg where (g = 9.80 m/s²)
3. Copy the data from Lesson 1, Table 1 for the columns of Force Before Mass Begins Moving (f_b) and Force While Mass Is Moving (f_m) into Table 1 below.
4. To find the coefficient of static friction (µ_s), divide f_b by f_g. This value is called the static friction coefficient because the mass is not yet moving. Calculate and record µ_s for each mass (1.0 and 2.0-kg) in Table 2.
5. To find the coefficient of kinetic friction (µ_k), divide f_m by f_g. This value is called the kinetic friction coefficient because the mass is now moving. Calculate and record µ_k for each mass (1.0 and 2.0-kg) in Table 2.