Physics 4.7.4a - Friction Practice Problems 1 - 2

Two practice problems dealing with friction.

[andrewkeilbart]

Thank you so much for your help! My physics teacher never bothered to show how to rearrange the formula to get a= g times the coefficient of friction, so I was trying for hours and I was never able to find out. But when I found this video, it was clearly laid out and explained, you are an excellent teacher, you saved my life just before my unit test!

[mvayne]

Thank you very much. I dont have the greatest physics prof in the world so much of what i learn is out of class. It would be a lot tougher if people like you didnt care to help us out with these type of videos.

[nutella]

Ahh thanks to this video, I just had a light-bulb moment. Much appreciated ;) You have lovely, legible handwriting and articulate explanations :D

[derekowens]

@99miyah Yes, that would be a very good way to set this problem up. You can define "to the right" as being the positive direction, and then the force of friction would be negative. That would be a pretty intuitive way to think about it.

[derekowens]

Yes, there will be a forward force on you, but right now we are concerned with the forces on the car, and only those forces. The forces on the car are the ones which determine the motion of the car. In fact, if the car hits you, the force on the *car* will be backward, not forward!

[tiang]

I wasn't born yet when the time he send this video

[derekowens]

@Itswalrus Yes, that will convert from km/h to m/s. That's a helpful shortcut.

[derekowens]

@brjesusfreak That's the acceleration due to gravity, in metric units.

[derekowens]

@owaisoz I do, lots of them! I just don't post them all here. Students who enroll in a class get access to all of the videos for the class.

[CadmiuM]

You have to start somewhere. Oppenheimer, Feynman, and Einstein even asked this question at one point or another.

[nasreenasif]

sir if the car is deacceelrating wont the acceleration be negative

[ewaschenko]

@UCSDMRod I think it comes from 10^3=1000, and 1h=60, 3.6 or something like that. It should always work.

[nasreenasif]

you sir are a life saver thank you so so much

[ewaschenko]

When converting km\h in meters can you just divide the number by 3.6? 90/3.6=25

[auspicious]

Can we say that the net force equals - f, because we determined that the positive direction is to the right, and the frictional force is opposing the car's motion?

[anantakhanal]

coefficent of static friction is greater than kinetic friction ? why

[owaisoz]

why dont u have videos about work, mechanical energy, and its conservation, momentum and collisions ?

[homebirding]

I don’t understand why A is negative in the second question, is it because you’re slowing down?

[TaraLynn]

I appreciate everything youve done here, but the symbol for the coefficient of friction is pronounced mew, not moo

[thefamilysmiley]

Let’s convert it and make it more confusing no thanks