How Do You Determine When to Use Static vs Kinetic Friction in Physics Problems?

[Coldchillin]

http://img175.imageshack.us/img175/2448/picture1wt8.png

I am having trouble deciding when to use the static and kinetic frictions and what to do about this problem. Thanks for any help!

 

[Doc Al]

If the surfaces slip, then you have kinetic friction; if they don't, it's static friction.

Start by figuring out if it's possible for the block to not slip on the slab.

 

[m2003]

I understand your frustration with frictional problems. The key to solving these types of problems is to first identify the type of motion involved. If the object is at rest or moving at a constant speed, then static friction is the dominant force. On the other hand, if the object is accelerating, then kinetic friction is the dominant force.

In the image provided, it appears that the object is at rest, so static friction would be the relevant force. To solve this problem, you can use the formula F = μsN, where F is the force of friction, μs is the coefficient of static friction, and N is the normal force. The normal force is equal to the weight of the object, which can be calculated using the formula N = mg, where m is the mass of the object and g is the acceleration due to gravity.

Once you have calculated the force of friction, you can use it to determine the minimum force needed to move the object. This can be done using the formula F = ma, where F is the applied force, m is the mass of the object, and a is the acceleration. If the applied force is greater than the force of friction, then the object will begin to move.

I hope this helps with your frictional problem. Remember to always carefully consider the type of motion involved and use the appropriate formulas to solve the problem. Good luck!