27-Sep-2014: Coefficients of friction stuff

a) Static friction with cup and water

1. set up the equirement as shown in the pictures. Add water in the cup until the one of the block starts moving. Weight the mass of the water and block. 

2. Putting one more block on the blocks before and repeat the last step. Repeat four times until the number of block is four.

 Record the data of the mass of block and mass of the water each time.

type the data in logger pro and caclculate the Normal force and Tension for each time. Use linear fit steacher the graph. The slope of the graph is the coefficient between the table and blocks. As shown below, the =0.257.

 b) kinetic friction with force sensor

Pull the force sensor and recored the data.

The slope of the graph shows the acceleration  which is 1.77m/s^2.

And the normal force of those four blocks is 5.71N. then a=(T-N)/m

 c) static friction from angle to get sliding

Set up the equirement as shown. Raise up the higher end of the track little by little until the block starts moving. Measure the angle between the track and table θ . 

Do a free body diagram.

mg*sinθ-mg*cosθμ=ma

μ=(g*sinθ-a)/g*cosθ=0.373

 d) kinetic friction from sliding block on a steep ramp

Set up the equirement as shown. Recored the data.

Make a FBD, the mass of the block is 100g, the mass of the block is 128g. The angle is 28degree. Acceleration shown in the Velocity Vs. time grap( the slope ) is 3.59ms^2
then a=(Mg-mg*sinθ-mg*cosθ*μ)/(M+m)
μ=(Mg=mg*sinθ-a(M+m))/mg*cosθ=0.373

e) predicting acceleration of a two-mass system—one

on a friction ramp, the other hanging.

Use the same formula in d) a=(Mg-mg*sinθ-mg*cosθ*μ)/(M+m) perdict the acceleration is a=2.92m/s^2