Physics Lesson: Pulley Systems Part 3 Dynamics for High School

[wishingstars163]

Hmm when did they start using F(parallel) and F(perpendicular)?? Is F(parallel) = F(gx)

and F(perpendicular) = F(gy)?

[wishingstars163]

This is officially my favorite channel! Thank you so much for explaining these concepts in concise explanations! You guys are my heroes! :')

[PhysicsEH]

@wishingstars163 Thanks for taking the time to let us know you liked our videos. Best comment ever!

[kws2015]

these videos are very helpful for me learning in college

[PhysicsEH]

@kws2015 Thanks for taking the time to let us know you liked our videos.

[PhysicsEH]

@kws2015 Thanks for taking the time to let us know you liked our videos.

[scl8114515]

I'm in college and these videos have been more helpful than my prof. Thank you so much

[playlist13579]

how do you know that the 10 kg object will pull everything down? Isn't there an inclined ramp....so the 5kg object could actually pull the 10kg down?

[wishingstars163]

@playlist13579 The inclination probably isn't steep enough to do that

[PatrickVedlog]

This was really helpful! I'm a high school student in Norway and this really caught my interest!

[AbawoyaH]

thanks soooo much for this... what a nice explanation

[RescuePits1]

kudos to such a CLEAN explanation. 

[nez349]

Isnt F(ii) supposed to be 5gcos30? Because its on the x plane right?

[imthekashmeister]

i want his beard

[PhysicsEH]

@imthekashmeister I want it too (I'm the other guy)

[rip111buddy]

we call F// as Fsinθ and F⊥ as Fcosθ

[mcaruana1]

@rip111buddy Hi. If it works for you then great. Thanks for letting us know.

[MaQWan93machanG]

why do the acceleration of 10kg object is +a instead of -a.. based on my understanding, when object goes down, the acceleration should be NEGATIVE , right? please EXPLAIN me.. and CORRECT my current understanding.. PLEASE,,.

[PhysicsEH]

@MaQWan93machanG You can set either direction as positive. Up does not have to be positive. When you solve pulley problems you must make sure that the sign convention for one object matches the sign convention for the other object. The easiest way to do this is to make the direction of acceleration positive. In some cases that means up is positive and others it means down is positive it just depends on which way you think they will accelerate. I hope this helps.

[yellopanda]

i would thank god, but he isnt real, soo... thank you zach galifinakis physics master !!!

[timmy11zoomsharecom]

Thank-you for making this video it helped me solve a very frustrating problem. just one question, I thought you would add all the equations in the x seperatly and then in the y seperatly.

In the video however, you added the x equation and the y equation together (which is correct) but I don't understand why you would do that

[PhysicsEH]

@timmy11zoomsharecom It does look confusing. What we are really doing is adding the equation for the direction of acceleration for object 1 to the equation in the direction of acceleration for object 2. The 2 objects are related by having the same acceleration, one of which may be in the x dir based on how we drew it's FBDiagram and the other in the y direction for it's FBD. The direction of acceleration is the deciding factor for which equations get added. I hope this helps.

[timmy11zoomsharecom]

@PhysicsEH thanks for clearing things up :) youtube needs more people like you :)

[PhysicsEH]

@timmy11zoomsharecom Thanks for the compliment. Glad to help.

[MiturBinlsderty]

I have one question, how come we add the equations together? What does that mean?

[PhysicsEH]

@MiturBinlsderty Adding the 2 equations works for this type of problem. One equation is for the 5kg object and the other is for the 10 kg object. You put the first equation above the second one (as in the video) and then add the top equation to the one under it to get a new equation. so on the left side the top "T" is added to the bottom "-T" which = zero. If you add all the other variables on the left you get the 10g - Ff-F. Add the right side and you get 15a. Solve for "a" if g = 9.8

[MiturBinlsderty]

why is physics soo hard...

[PhysicsEH]

@MiturBinlsderty So that when you learn it you have something to be very proud of. Keep at it. Best of luck.

[MsLemonade17]

so, should the tension be 54.7 instead of 16.9 since acceleration changed from 8.1 to 4.33??

[PhysicsEH]

@MsLemonade17 Hi. Yes, we missed that. Thanks, I made a note on the video that it should be 55N (rounded off)

[MsLemonade17]

@PhysicsEH oh it should be rounded off, sorry :) you're welcome

[4Rambo7]

@PhysicsEH I don't understand how you guys got 55N in the end....T=10g-10a gives me 17????

[PhysicsEH]

@4Rambo7 Hi. We have a mistake at 4:38 where the acceleration should have been 4.3 m/s^2 and not 8.1 as written on the board. This changes the answer to T=10g-10a so that it is T=10(9.8) -10(4.3) If you solve this you get 55. I hope this helps.

[4Rambo7]

@PhysicsEH thank you your lessons help me a lot

[PhysicsEH]

@4Rambo7 Thanks for letting us know. We like to hear that they help.

[kt11020]

@PhysicsEH Thanks!

[raptors12349]

@PhysicsEH what would u do if the weights r the same

[timsss128]

So... the acceleration should have been 4.3 m/s squared right?

And not 8.1

[PhysicsEH]

@timsss128 Oops. Yes, I have to put a correction in it to fix our mistake. I hope you still found it useful. Thanks for the reminder to fix it.

[sarcasm2182]

i fuking hate physics

[SadegoGG]

@sarcasm2182

Physics is actually extremely easy. The problem is most teachers (Like the one in the video) presentation is terrible and don't properly account for all the assumptions they make. They also randomly introduce formulas in the middle of a problem, which is the incorrect way to approach mathematics.

If mathematics were taught in schools as a language rather than a more advanced way to add, subtract, multiply, and divide it would make physics seem much easier.

[sarcasm2182]

@SadegoGG to be honest I don't hate physics I actually thing physics and all the other type of sciences like chemistry are quite cool and interesting I just hate my ohysics teacher for sucking so much at teaching -__- !!!

he really sucks

[SadegoGG]

@sarcasm2182

Then just go on youtube and learn the lessons he covers in class on here...Which it seems like you're attempting to do.

[ljohnbird]

Love the videos - it's been >10 years since I've looked at any of this, but your examples are great - very clear and easy to follow.

Ditto what the other commentors have said re: calculations ----- 10g - 9.8cos30 - 49sin30 = 65.01295 ----- divided by 15 = 4.33

Since friction is 1/5 the force of gravity (mu=.2) it would be very strange if the decrease in friction made a larger change in total accel than the drop in directly applied gravity.

[Lithiumz]

Well if you used g = 10ms^-2 then => [100-(0.2*50*cos(30)) - 50*sin(30)] / 15. In the bracket you'll get ~66.34, that divided by 15 is ~4.42. Even if you use 9.8ms^-2 as g, you'll get what AllanIsPimp did. I think your calculator wasn't in degrees mode but radians. By the way any chance you'll cover larger portion of physics other than mechanics? Oh, I find the videos more than helpful.

[NeoGear]

@Lithiumz

I got 4.33 as well o.O

[Lithiumz]

nice demonstration but the algebra is wrong.

[PhysicsEH]

@Lithiumz Hi. If there is a mistake, let us know where so we can fix it. I hope you still found the video helpful. Thanks.

[AllanIsPimp]

isnt a= 4.33m/s^2 ??

[AllanIsPimp]

nice videos