Friction Lab Troubles: Finding Static & Kinetic Friction

[ariana0923]

My problem is with this lab on friction...it is a virtual lab, as I attend a virtual high school. I've put in numerous hours and can't seem to figure out what is wrong. You see, we need to determine max static friction and kinetic friction using this program. For all the objects EXCEPT the dog and crate, I did this. But for those 2, there was never a point where the friction dipped...in another words, kinetic never got lower than static, which I KNOW is incorrect.

My teacher tried to show me, but now I can;t seem to replicate what she did...she said that kinetic is when the net force=0, both the applied and frictional forces are equal, BUT the object is still moving. Is that correct?

If you could please explain to me how to use this program to find static and kinetic friction, I would GREATLY appreciate it.


http://phet.colorado.edu/simulations/sims.php?sim=Forces_in_1_Dimension



I do have screen shots to show what I am getting...they explain better:

http://i38.tinypic.com/16kchsp.jpg



Where am I going wrong??

Thank you so much!

 

[LowlyPion]

Welcome to PF.

With the dog - the coefficient of static friction for all that shaggy hair is the same as for the coefficient of kinetic friction and is only .1. Once you apply 25N to the dog, that puppy will be in motion. You won't see any sudden changes in force from friction as it switches from static to kinetic.

The filing cabinet is heavier and the coefficient of static friction is greater (.3), kinetic is .2, so it takes more force to get it started 200*.3*9.8 = 600 and then once moving it drops back to 200*.2*9.8 = 400.

 

[thomate1]

Dear student,

I understand that you are having trouble with the virtual lab on friction and are unable to determine the max static and kinetic friction for the objects in the simulation. I can assure you that your efforts and time spent on this lab are not wasted, as understanding friction is an important concept in science.

Firstly, let me clarify that kinetic friction is the force that opposes the motion of an object when it is already in motion. On the other hand, static friction is the force that prevents an object from moving when it is at rest. In order to determine the max static and kinetic friction for the objects in the simulation, you need to understand the concept of the coefficient of friction.

The coefficient of friction is a measure of how much force is needed to overcome the friction between two surfaces. In the simulation, you can see that the coefficient of friction is represented by the Greek letter "mu" (µ). This value is different for different materials and surfaces. In order to determine the max static and kinetic friction, you need to find the point where the applied force is equal to the maximum frictional force, which is µ x the normal force.

To do this, you can use the following steps:

1. Start by selecting an object and placing it on the surface.
2. Adjust the applied force using the slider until the object starts to move. Take note of the value of the applied force.
3. Increase the applied force gradually and observe the object's motion. At some point, you will notice that the object is moving at a constant speed. This is the point where the applied force is equal to the maximum frictional force.
4. Take note of the value of the applied force at this point. This value will be equal to the maximum static friction for the object.
5. To determine the kinetic friction, decrease the applied force gradually until the object starts to slow down and eventually stops. Take note of the value of the applied force at this point. This value will be equal to the kinetic friction for the object.

Repeat these steps for each object in the simulation. It is normal for the kinetic friction to be lower than the static friction, as the object is already in motion and less force is needed to keep it moving.

I hope this explanation helps you to understand how to use the simulation to determine static and kinetic friction. Remember, practice makes perfect, so keep trying and don't hesitate to ask your teacher for further clarification. Good luck with your virtual lab