22-Mar-2017: Modeling Friction Forces

In our daily life, we know that everything will have a friction force when contact with other objects. However, we can only roughly know that when we push the objects harder, the frictions become greater. In today's lab, we did five experiences on a block with linoleum in the bottom to detect the relationship between fiction and "push" (normal force) in moving and stable.

Set up:

Experiment 1:

We set up the instruments as the following picture, and addingthe hanging mass piece by piece carefully. When it fell down, we took out the last 5g mass and take that weight as the smallest friction force to make the block move.

Then, we add some weight on the block and repeat the steps we did just now. The result is showed as following. 

Experiment 2:

This time we set up the instrument with force sensor. To make the block get a stable friction force, we pull the board instead of pulling the block (which might give different force because it is hard to provide a real stable force). 

Then, we got the data as following. 

The friction force is around 0.5197 N. 

Experiment 3:

This time we used the slope to calculate the static friction coefficient. We rose the slope slowly and collected the angle when it just began to slide. 

We get the angle is 24˚

Expriment 4:

Using the slope with 24˚, the block will silde down automatically. 

Then, we collected the data. 

Experiment 5:

Eventually, we set up the instrument as following. 

Then, we hanged total 100 gram mass on the hanging mass and get the data. 

Analyze:

For the expriment 1, by the function

We can know the slope of function is the coefficient of static friction, and it equal to 0.4125. 

For experiment 2, because 

We can get the coefficient of kinetic friction is 0.276. 

For expriment 3, drawing the free body diagram we got

because

we got 

In this case, the coefficient of static friction is 0.445. 

For experiment 4

From the graph, we knew that the acceleration is 1.9 m/s^2, then by functions 

we can get 

In this case, the coefficient of kinetic friction is 0.233. 

For experiment 5

In the graph, we can know the acceleration is 1.912 m/s^2

By Newton Second Law, we can get 

Then, the result is 

then, we got a = 1.919 m/s^2, and it is only 0.007 off the real value. 

Conclusion:

In this lab, we used the functions

to detect the real coefficient of friction, and we applied it in a model, which is pretty success. 

Therefore, we can assume those two function is applied for the most situation of contect friction.