Purpose: through the experiments and building the model to involve ftiction.
Model: μs = fstatic, max/N, μk = fkinetic/N, F = fkinetic, a = sinθg - cosθμkg,
sinθ = cosθμS, μk = (a(M+m)+mg)/Mg
μs is the coefficient of the static friction, μk is the coefficient of the kinetic friction, f is friction, N is normal force, and θ is the angle of the borad.
Process: Part 1: Static Friction
We place the block on the flat board and use a string which one side tids on the block, and the other side hang a mass and cross through the pulley.
We weigh the block to get M, and then we keep add mass on the other side of the string until the the block just begin to move. We record the hanging mass. Then, we add a 100g mass on the block and keep add mass on the hanging side until the block just begin moving. Repeat this process five time, record the M and hanging mass m.
Then, we get the datas:
M m
0.18 0.056
0.28 0.085
0.38 0.160
0.48 0.235
0.58 0.320
We plug these datas into LabPro and use the liner fit. Accoring to the model:
μs = fstatic, max/N
The slope of the line is μs. We get the μs = 0.48.
Part 2: Kinetic Friction:
In this experiment, we use LabPro and force sensor to collect data F. First, we calibrate the force sensor by using 0 g and 1000g. Then, we weight the block to get the block's mass M. We put the block on the flat board, and then we pull it with a constant speed. We use the Excel to get the average force F. Then, we add 100g on the block and pull it with a constant speed. Repeat it five times and record the datas.
We get the datas:
M F
0.18 0.52
0.28 0.79
0.38 0.94
0.48 1.24
0.58 1.47
We plug these datas into LabPro and use the liner fit. Accoring to the model:
μk = fkinetic/N, F = fkinetic
The slope of the line is μkg. We get the μk = 0.263.
Part 3: Static Friction From A Sloped Surface:
We place a block on a horizontal flat board, slowly raise one end of the board, tilt it until the block starts to slip. Then, we use our phone to measure the angle of the board θ. θ = 22°
By using the model:
sinθ = cosθμS
We get the μS = tanθ = 0.4
Part 4: Kinetic Friction From Sliding A Block Down An Incline:
We put a motion detector at the top of the incline which steep enough that a block will accelerate down the incline. We measure the angle of the incline θ and the acceleration of the block a by using motion detector.
We get a = 0.82 m/s^2, θ = 25°
By using the model:
a = sinθg - cosθμkg
We get μk = 0.37
Part 5: Predicting The Acceleration of a Two-Mass System:
We place the block on the flat board and use a string which one side tids on the block, and the other side hang a mass and cross through the pulley. Then, we hang some mass which are enough to let the block accelerate. We use the motion detector to measure the accleration of the block a. We weight the block and the hanging mass M and m.
We get a = 2.65m/s^2, M = 280g, and m = 250g.
By using the model, and the μk from last experiment:
μk = (a(M+m)+mg)/Mg, μk = 0.37
We can calculate the ac = 2.71 m/s^2.
Conpare a and ac, we get two very similar result.
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