Static and Kinetic Friction

[joasten]

I've never learned something like that so fast, but when is this supposed to be learned (At what age?)

[Starcross42]

@joasten We present this to advanced High School students in a class know as AP Physics. We mention it at the middle level physics class, but seldom do this level of problem. It isn't difficult math, but it is a long train of though that must be constructed. Watching me do it is easy... doing it yourself is more difficult. If you want to do it yourself you must practice.

[joasten]

@Starcross42 How can i calculate Mk?

[oleboy96]

thank you sooooo much!!!!

You saved my live!!!!!!!1

[TheMrHafooz]

i love this example

[YouEatSht]

i hate my physics teacher. she is so cocky and gets things wrong.. and i feel a teacher shouldn't get things wrong when theyre teaching. then she makes up an excuse and say, i wanted to experiment with you guys and see if you can see what i did wrong.

[Starcross42]

@YouEatSht I'm sorry about your physics teacher. As a teacher it is embarrasing standing in front of the class and making a mistake. You teach all day and you can't help but make a mistake now and then. And after 30 years I don't mind admitting that I don't know everything. In fact, the main emphasis of my class is to think for yourself. Solve problems and learn techniques to help solve ANY problem. but good luck with physics. I have a lot of videos that might help you.

[xDemon2x]

@Starcross42 why is static friction greater than kinetic friction?

[Starcross42]

@xDemon2x If the materials are not moveing then some of the molecules can actually form weak (in some cases, strong) bonds between the surfaces. If they are moving then those things are not part of the mix so there is a bit less force.

[Prillyfied]

better than my physics teacher! thank you!

[kabilan83]

im studying at @starcross42 university :D :D thanks dude

[Starcross42]

@kabilan83 Hey, click on an add now and then. I get paid.

[lllBOLTlll]

I need help on my statics. lets say we have a car and its moving at 5mph and has unknown angle for hill, & friction is .5. I understand how i can solve for everything, except i'm clueless on how to find the N of the car?????? i have to find the angle in the end of it all.

[Starcross42]

@lllBOLTlll I use mgcos theta for N in this problem. I lost cos theta because the angle was zero. Simply keep it for your problem. If you have everything else then solve for theta!

[lllBOLTlll]

@Starcross42 but the car isn't specified on how much it weighs. if i knew how to solve for the weight with two unknowns that'd be great, but i was thinking with speed i can solve acceleration then friction then force then weight but i'm an amateur and can't do it properly. THX for the help though.

[Starcross42]

@lllBOLTlll Sorry. Let's try this. If car is NOT accelerating then Net F = zero

So force down the ramp is mgsin theta and that should be equal to Ff (mu mgcos theta)

Divide and cancel out mg and you end up with mu = tan theta. If the car is parked then mu for static friction, and if it is moving AT A CONSTANT SPEED then mu for kinetic friction. mg will cancel out of both sides.

[dReMiNg09]

thank you. :)

make more video.

it's really helpful

[samzzzzzzzzzzzzzzzzz]

Thank you!

[lanzxy]

Thank you :)

[PockyPuri]

I UNDERSTOOD!! lolol finally I got it, thank you!

[FISHO701]

this helped me aloott :)

RESPECT !!

[SOOFLY92]

it sucks how i have to pay tuition for an idiot 2 be my professor when id happily pay yu 2 make my semester soo much easier while taking physics

[Starcross42]

@SOOFLY92 Tell me about it.

Listen, if you really want to make physics fun then go to my laser videos and click on the adds. Find some great deals on lasers for the lowest prices. Then make the laser show and bring THAT to class. Sometimes physics teachers just don't remember how amazing it is.

and my webpage (listed on my homepage) has a lot of my classroom videos sorted by topic. I'm improving that site regularly. Good luck.

[PureAwesomeChiz]

Very well brought dude XD..the way you handled your explanation actually makes it more interesting...thx for the info

[annakolod]

Thanks so much, you're an excellent teacher !!!

[MeMyselfAND1ix]

what took my teacher to explain for a week ( didn't understand) , took you 5 min and i fully understand. You are aGreat teacher

[SpeedBoost100]

Be my teacher? :)

[Starcross42]

@SpeedBoost100 Thanks.

[FullofAwesomeness101]

I just wrote pretty much my whole research paper about static and kinetic friction from this video!!! Thank you! :D

[Starcross42]

@FullofAwesomeness101 Glad to help.

[zezo7hdk]

greetings*

[zezo7hdk]

thankss so much this really helped me alot!! greatings from qatar :)

[99miyah]

Thank you so much! This is very helpful. Do you have any videos covering other chapters of this textbook?

[Papu1234]

Can you solve the coefficent of kinetic friction by just knowing the mass and force of kinetic friction? I hope you understood what I was trying to say, I have a little problems expressing this question in english since its not my first language.

[atlass8]

that HAHA!! at 2:26 made me laugh out loud, n the way i waz stressin out tryin to understand this topic.. but after the laugh i cheered up n everythin seemed easy lol

[t3habaddon]

I learned more in your simple video then I did in a week with my teacher. Thanks.

[x20Mike07x]

Nice and simple to understand. Well done :-)

[TundraMike1]

Thank you so much!!! Are you still doing these videos. I see this one was in 2006. I am currently taking Physics but they didn't have it in house so I am having to take it online and struggling. I was wondering if I could ask you some questions every once and a whille

[NYSPINNERDAN]

This helped me understand static friction! Thanks so much!

[farhanafzal4786]

u r gr8

[Jorawar69]

Turned out I knew it all already but nonetheless I have to say that's a very good video, far better than most teachers who have the advantage of standing in front of their students.

[RolloJay]

thank you

[cfrazlit]

you are a great teacher.

[gehwe]

Dude, seriously. I would love for you to replace my current teacher. Your 5 minutes took up her 2 and a half hours.

[Starcross42]

Sorry man. Everyone has strengths...

[bllvv]

PLEASE replace my physics teacher!!

It took me about two weeks to understand what you've taught in a matter of five minutes. Your students are very lucky.

[princessmaldita23]

how come that when you get the mass and acceleration the unit is not canceled out???for example 30N/9.8m/s2= 30.6 kg ?...can you pls. explain to me...hellppp..because i cannot understand our lesson..=(

[Starcross42]

The N stands for Newtons (Yes, I knew that YOU knew that but other people reading this might not). A newton is a unit of force which is found by multiplying a mass times acceleration. If you divide that by units of acceleration (9.8m/s/s) then you will be left with units of mass... (kg).

So 30N / 9/8m/s/s could also be written (this will be messy) as 30 kg m/s/s / m/s/s. All those m/s/s will cancel out leaving you with kg. Hope that helps.

[cryptblood1986]

@princessmaldita23

N = (# x kg x m/(s^2))

therefore

(30 x kg x m/(s^2))/(9.8m/(s^2))= will be 3.10kg

the m/(s^2) cancel out leaving you with the kg answer above.

[SirAMedd]

Wow I love Physics

[McPlaz]

omg i'm in 4th grade what the hell am i doin?

[Starcross42]

Every 4th grader should be able to do this... by the time they are in 10th grade.

[jn30]

good point!

[jexx10]

physics is so fun, thank you!! :D

[fatshadow92]

Physics*

[fatshadow92]

thank you so much!

by the way what book are you guys using? because we are chapter 4 to with friction

we are using the Holt Phyiscs book that has a light bulb on it

[Starcross42]

Sernway Faughn, but most of the books are VERY similar. I helped to write a text book and we got a LOT of flack because we wanted to do things differently.

[GameKingFaiz]

Thank you!

[Starcross42]

glad it helped.

[Starcross42]

The force of friction is equal to the normal force (weight x cosine of the angle) times the coefficient of friction.

[rpottsch]

thanks man!

[BonanzAA]

THANK YOU SOOO VERY MUCH!!! I'm struggling with Physics and I'm glad you've posted a lot of videos. I have a test coming and your videos will help me a lot for sure!

[yeloopanitsirhc]

Wow thanks, you're so good at what you do :D

[mcdebaca]

Thanks a lot for your videos.

Your work is really appreciated.

[Starcross42]

Glad you like them. Thanks for the kind words.

[mmmporkchopmmm]

omg thank you so much for teaching me, our teacher is out for 6 weeks, and we are on our own cuz the sub doesnt know what shes doing

-thank you so much!

[Starcross42]

Have you seen my other videos?

If you have a specific question I can create a specific video for you.

[speedmetal0789]

try and keep the camera still

[Starcross42]

It's mounted on an extension arm over my work area. I'll try and brace it better.