PHYSCIS Writing assignment

Calculations

1. Using the mass of the block and the average force of kinetic friction from Data Table 1, calculate the coefficient of kinetic friction from Equation 1:

Ffr(k) = uk FN. Therefore mk = Ffr(k) / FN

.87N= uk (4.11N)

uk= .87N/4.11N

uk= .211N

2. Using the mass of the block and the average force of kinetic friction from Data Table 2, calculate the coefficient of kinetic friction for the wood block sliding on its side. Record your results and see how it compares with the value of Uk obtained

from Data Table 1.

Uk = Ffr(k) / FN

Uk= .88N/ 4.11N

Uk= .214N

It is very similar, which leads me to conclude that sliding friction is proportional to the mass of an object, not the surface area.

3. From the data in Data Table 3, 4, and 5, compute the coefficient of static friction, Us, for the

glass surface on wood, the sandpapered surface on wood, and wood on carpet, etc., from

each of your three trials. Calculate an average value of Us. Record your results in your own

data sheets.

Glass                           

Us = Ffr(s) / FN

Us= .6N/4.11, 6.N/4.11N, .5N/4.11N

Us= .15N, .15N, .12N

Us average= .14

Sandpaper

Us = Ffr(s) / FN

Us= 1.7N/4.11N, 1.8N/4.11N, 1.7N/4.11N

Us= .41N, .44N, .41N

Us average= .42N

Carpet

Us = Ffr(s) / FN

Us= 2.4N/4.11N, 2.4N/4.11N, 2.3N/4.11N

Us= .58N, .58N, .56N

Us average= .57N

4. From the data obtained in Data Table 6 calculate Us for wood on wood from each of your three

trials.

Us = tan θ = sin θ max/ cos θ max or Us = tan θ = height/base

Trial 1= tan 22.3= .41 or 25/61 = .41

Trial 2=tan 22.1= .41 or 26/64 = .41

Trial 3= tan 22= .40 or 25.5/63= .40

5. Calculate an average value of Us. Record your result on the data sheet.

(.41+.41+.40)/3 = .41

Questions                                                                                                          

A.  Howdoesthecoefficientofstaticfrictioncomparewiththecoefficientofkineticfrictionfor

thesamesurfacesand areas?

The coefficient of static friction is always larger than kinetic friction for the same surfaces and areas. This is because it takes more force to get an object moving than to keep it moving.

B.   Why is it important to reduce frictionduring the operationof machinery?

If you reduce friction during the operation of machinery you will increase the energy efficiency of the machine which will allow you to get more work done without having friction act against you.

C.   How does grease or oil affectthe coefficientof friction?

Oil and grease are used to decrease the friction between two objects. This allows machines to operate more efficiently by reducing energy lost.

Summary- Overall I conducted an experiment to find out how much friction different surfaces had sliding over each other, and also wanted to find out if it took more force to get something moving or keep it moving. I learned that it takes more force to start something moving than to keep it moving, and also learned friction is proportional to mass of an object and texture rather than surface area. I also learned about how to calculate what degree an object will break free of friction if I know the coefficient of static friction, and how to find the coefficient given the height and length of a ramp that a block starts moving on.