Uniform Circular Motion: Crash Course Physics #7

Did you know that centrifugal force isn't really a thing? I mean, it's a thing, it's just not real. In fact, physicists call it a "fictitious force." Mind blown yet? To explore this idea further, this week Shini sits down with us to discuss centripetal force, centrifugal force, and a few other bits of physics to help us understand uniform circular motion.
***
Produced in collaboration with PBS Digital Studios: / pbsdigitalstudios
Crash Course is on Patreon! You can support us directly by signing up at / crashcourse
Thanks to the following Patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:
Mark, Eric Kitchen, Jessica Wode, Jeffrey Thompson, Steve Marshall, Moritz Schmidt, Robert Kunz, Tim Curwick, Jason A Saslow, SR Foxley, Elliot Beter, Jacob Ash, Christian, Jan Schmid, Jirat, Christy Huddleston, Daniel Baulig, Chris Peters, Anna-Ester Volozh, Ian Dundore, Caleb Weeks
--
Want to find Crash Course elsewhere on the internet?
Facebook - / youtubecrashc. .
Twitter - / thecrashcourse
Tumblr - / thecrashcourse
Support CrashCourse on Patreon: / crashcourse
CC Kids: / crashcoursekids

[@crashcourse]

We made quiz questions to help you review the content in this episode! Find them on the free Crash Course App! Download it here for Apple Devices: apple.co/3d4eyZo Download it here for Android Devices: bit.ly/3TW06aP

[@dezent]

She kept me totally focused for nine minutes and twenty six seconds and i learned lots of new stuffs i did not know before!. Really shows that you guys are getting more and more professional.

[@LeRouxBel]

Great, now I lost my key.

[@rat7710]

I lost my ignorance :)

[@carmelogonzales5053]

I use a Knife My key is safe

[@carmelogonzales5053]

That flying Hit my brother and now his gone. Lol i have no Brother.

[@davidcobb2682]

@@carmelogonzales5053 not any more

[@AxisSpark]

2:45 The fact that phys is a required course for Computer science majors with a concentration in game development and crash course incorporates video game references in these videos makes learning all the more enjoyable!

[@mufaddalezzi2293]

just an idea, you should have an app where you can compete in a quiz with a stranger based on the material from your videos. It would help learn better.

[@amnawajahat6418]

quizup

[@jessmoser7322]

or quizizz

[@sharathkumar8422]

This is a brilliant idea to increase revenue and viewer count... CRASH COURSE! LOOK AT THIS!!!

[@kynslayer]

Mufaddal Ezzi quizcourse

[@calebmeeks442]

so a review just do quizlet

[@WriteUnread]

Please god someone fix that Rubik's cube I'm dyin here

[@thelonelydirector]

+Holly Panetta I have bad news for you ;)

[@WriteUnread]

+thelonelydirector :(

[@thelonelydirector]

Blame Hank, he's the one who started playing with the cube in a meeting and now it's forever that way. FOREVER!

[@WriteUnread]

+thelonelydirector :(( my poor order-loving brain can't take this

[@MARK_2130]

When I play rubic's cube sometimes I cheat it

[@drink15]

Hank is looking good!

[@rileypurcell2159]

+leein jeon Hank usually hosts the CCs that are filmed in Montana.

[@djbslectures]

Who the eff is Hank?

[@drink15]

DJBsLectures I hope this is the first video you watched on this channel.

[@djbslectures]

+drink15 store.dftba.com/collections/vlogbrothers/products/who-the-eff-is-hank-poster

[@drink15]

DJBsLectures OOOOOoooooo. Well played sir!

[@krismoe31]

I am at the bottom of motivation atm and I have a physics/chemistry exam in 1.5 weeks. So nice to have easy "lectures" on youtube. Thank you guys!

[@vectoredthrust5214]

"We're just here to make sure the ride is safe, we're not responsible to clean up all the vomit after the ride is over" Bahahaha, I'm sure the engineers agree xD

[@MartinPereira-qn2mt]

+Vectored Thrust That's the rocket builders motto

[@zhto514]

Last video 5 years ago bruh 😃😅

[@fredschwartz3654]

Great video. I'm close to 70 and live in the US, but when I was her age, we pronounced about 73% percent of all those big words differently :-) , Love it. I could listen to this video a dozen times. (and might have to . . . and take notes)

[@simplySwag7567]

I remember when i was back in 8th grade i couldn't understand a thing she said. I jus thought she was one bad teacher with crash course. now in tenth grade, this is the most clear explanation i have found yet. Thanks!!

[@neilsanders8163]

No idea is original, everything stems from something. To brake it down the more you understand the basics, the easier all the new stuff gets. You can't have the newest phone with out starting with the Nokia brick A.K.A THE OG (the struggle was real).

[@TGC40401]

You spin me right round... Thank you for your time.

[@Sleepy_Fox]

😂 nice one 😂

[@killersquirrel9]

I just failed my ap test this week, really could have used this earlier rip

[@crashcourse]

+Yale Benson I mean... I usually know when I've failed an exam.

[@killersquirrel9]

+CrashCourse ya... Not answering half of it was my first clue

[@leaderoftaehyungnation9766]

Can't you re sit the test?! 😪

[@frankschneider6156]

+Dan Gilbert Learning sometimes helps .. just a thought

[@ZVPieGuy]

This video wouldn't have helped you on the AP at all.

[@seantimchew]

Bless you guys, this has practically saved my GPA. So much easier to understand than what's taught in school

[@meredithmcdonough5885]

currently watching this 3 hours before my AP test. god bless your soul

[@dm_nimbus]

Why is Crash Course always awesome? Is there some quantifiable element?

[@mjpanicali]

+James Craver CC Physics is 2.7 less quantum units of awesomeness than CC Government and Politics (no eagle punching is negative factor).

[@Byamarro2]

+James Craver Now I know from where Kurzgesagt seeks for materials, haha

[@bananaman7458]

Kurzgesagt is awesome!

[@dm_nimbus]

+Bananaman Agreed (I'm a patron with a bird profile pic; not actually affiliated with them)

[@imaaduddinshaikh221]

It smells like months of hard work Famm

[@TheWizardYoshi]

Circular motion was my favorite section of physics last year, awesome video!

[@nachannachle2706]

It's interesting to notice that as we go further into these videos, the explanations make more and more (intuitive) sense. That's is great course outline work, folks!

[@SotraEngine4]

This will save me in the physics exam in 12 days

[@rainick]

+SotraEngine4 Sounds like you need a better physics class.

[@dragonjade8853]

SotraEngine4 same

[@oogabooga8447]

this will save me on the physics exam in 16 hours. and i have the flu.

[@ExplodingPinapple]

2:47 Oh hi there, Link! How are you?

[@betatree]

Damn these physics crash courses are super clear! I hope it'll help a lot of people struggling with their mechanics class :)

[@zachariahfurlotte]

Hey guys, awesome videos ! You guys have been teaching me material non stop all the way from grade 10 Advanced Biology to first year university Psychology and I just wanted to thank you for all your dedication and hard work ! I just transferred from a BSc to BEng and am studying to become a Material Engineer so I'm taking several physics courses in the spring/summer and am exactly where you guys are right now(Video Wise) ! P.S. I think I've gotten almost all my friends to watch your vidoes if they need help ! :D Thanks for all the dedication guys !

[@Kaalyn_HOW]

The key turning 'experiment' is basically how discus throwers don't knock out anyone standing beside/behind them.

[@brennahasselmann8075]

I love that you explained how the variables in each equation made sense in reality, that's the one thing that was keeping me from understanding

[@perpetualpolymath5961]

1.Lets prove a = v^2/r if v = (2 x pi x r)/T 2.v= (2 x pi x r)/T 3.using chain rule 4.dv/dr x dr/dt = dv/dt = a 5.therefore dv/dr x v = a 6.dv /dr = (2 x pi) / T 7.dv/dr x v = ((2 x pi)/T) x ((2x pi x r)/T) 8.dv/dr x v = (4 x pi^2 x r)/T^2 9.dv/dr x v = (((2 x pi x r) / T)^2 )/r 10.we know that v = (2 x pi x r) / T 11.therefore 12dv /dr x v = v^2 / r 13.hence 14.a = v^2/r 15. Q.E.D if anyone is confused at 9 a quick expansion shows that line 9 equals line 8.

[@saeedbaig4249]

"4.dv/dr x dr/dt = dv/dt = a 5.therefore dv/dr x v = a" I can't see the leap of logic u made from 4 to 5. When u say "dv/dr x v", r u saying that v is dr/dt? I that it v was dc/dt (where c is circumference).

[@perpetualpolymath5961]

Sideeq Mohammad Simple chain rule is at work here. dv/dr x dr/dt =dv/dt , think of it like the dr's cancelling but the actual proof for chain rule is quiet long. we know dr/dt is basically the rate of change in distance and we all know that is velocity.dr can be exchanged for dx here thus dr/dt = v hence dv/dr x v = dv/dt = a.

[@saeedbaig4249]

Mo Killem Ok Im familiar with chain rule now but, as an aside, shouldn't dr/dt=0? After all, dr/dt is the rate of change of the RADIUS with respect to time. But the length of the radius NEVER changes in uniform circular motion.

[@perpetualpolymath5961]

Sideeq Mohammad It doesnt change in magnitude however it changes in direction and hence it does have a rate of change.After all displacement is a vector.

[@saeedbaig4249]

Mo Killem O ok sanks 4 clearing dat up

[@christinarobyn9820]

I'm in university physics and these videos are incredibly helpful! Thank you

[@OmicronVega]

@Dr. Shini Somara You're just the whole package. I could listen to you could talk physics for hours. :)

[@realmenchangediapers]

Why did I live to the age of 34 before I found out that centrifugal force doesn't exist??

[@Eveseptir]

+realmenchangediapers It exists relatively speaking.

[@HaydenHatTrick]

Yeah, I get annoyed when I try and explain physics to people and they refuse to use fictitious forces. Because "their not real" Actually, you can think of fictitious forces as forces experienced due to being confined to a surface during motion. Because that is an entire field of math in its own, simply using forces produced relative to the object on the confining surface is stupidly efficient and true to what you actually experience.

[@SidPhoenix2211]

i found that out in a Horrible Science book, when I was in sixth grade

[@tutocfproductions7065]

So if it doesn't exist, why do we build things based on it and they work perfectly?

[@h20falcon59]

we don't centrifugal is just a name we give the machines we base them on centripetal forces, if for instance centrifugal force did exist, we wouldn't be able keep satellites in orbit they would go further and further away from the earth, and those centrifugal machines, have an arm attached to a giant pole in the center for a reason. :)

[@LucasCamargosRamos]

1:21 I was pretty concentrated on the video and thought I was just about to pass out. Well played. 10/10.

[@sondirobianto1548]

please make crash course programming

[@noirerequiemii101]

That'd be a dream. But VERY LONG

[@fossilfighters101]

+

[@undergroundskeptic2916]

YES

[@ShamsaShakir]

+

[@chlojo]

We now have Crash Course Computer Science. That's pretty good

[@DistortedMatt]

Too bad this was posted after the AP Physics Mechanics test! Still a great video and I am happy that Crash Course isn't afraid of covering a math heavy subject like physics.

[@Autotunethyeveryday]

CRASH COURSE IS IMPORTANT ALWAYS

[@jassenbuerano]

man, you guys should have done this last year, it's literally perfect for AP physics review.

[@FrumpybutSuperSmart]

Everything in this one made sense! I think I'm learning things.

[@ahorrell]

She has the best hair of any Crash Course host, WAAAAAAAAY better than Craig from Crash Course politics.

[@thenellecornejo3724]

time to re-watch this 5 more times

[@TheSYLOH]

"I'm getting dizzy just think about it" She said as she cut to a graphic of SPINNING GEARS.

[@reebam8914]

You videos have helped me so much in Physics. I couldn't find any reliable, informative and yet interesting video like these ones. I can't thank you enough. I'm more than thankful to you. 😊😊😇😇

[@buenchiko007]

this came at the right time to reinforce what i already knew about circular motion in a cool, graphical way for my exam tomorrow. Thanks for this upload!

[@harmonyofnature4747]

Homegirl in the video is really beautiful and very well spoken

[@BeHappyTo]

+Harmony of Nature almost distracting

[@Nemoticon]

+Harmony of Nature Dr. Shini Somara... I believe she's Indian.

[@user-bl8cm9pw8i]

Hi this video was so amazing keep up the good work love you all so much

[@sexysexminecraft]

"They knew a big part of space flight involved acceleration" -biggest understatement in history.

[@AliKhan-ox3mr]

So What is the REAL big part of space flight?

[@AliKhan-ox3mr]

So What is the REAL big part of space flight?

[@TakaG]

+CrashCourse Small tip. The editing is too fast. You are not giving the viewers any time to take in what they just heard before going into the next sentence or point. Leave a small breather. Just a second may be enough. Don't rush things, especially with scientific subjects like this one.

[@j26walker]

It's called crash course for a reason.

[@TakaG]

j26walker The things I have listed have little to do with actual crash courses and more with video editing. Many videos, especially on youtube, are edited poorly and way to quickly with awkward pace shifts. Giving small breathers helps the viewers digest what they just saw and heard. And keeping a proper pace and changing it at the right moments also helps with conveying information and mood. This applies not only to educational videos, but movies and everything else as well. An appropriate rhythm is important. That's the difference between the Transformers bad edits and the Avengers great ones. ;) That said, Crash Course usually does a very decent editing job. This video was way too quick paced though.

[@amsed7942]

Takako Jin I mean you can pause the video

[@bhaktisagar4089]

Jst watch it more den 1 time

[@dragonjade8853]

If on phone, try slowing any video down to .75. It helps

[@Sentinalh]

That was a lot of math, but I think I got it. Also Shini is beautiful.

[@kolbeowen3052]

1:22 the editing though

[@mantasreika]

She is so good!

[@thegaspatthegateway]

thank you thank you for the visual representation! (color coding the variables / connecting the variables with a line was also a nice touch :) )

[@riyam02]

Brilliant course with this one, and a very intelligent instructor. It's well broken down, and conceptually it just makes sense in under 10 minutes.

[@Ashley__Elyse]

This video explained Uniform Circular Motion in nearly ten minutes better than my teacher in almost a week. Thank You!

[@alanbannister1874]

I love how they have the ‘Feynman lectures on Physics’ on the shelves. Great books.

[@alexismonster64]

I was whating for this one for a while

[@crashcourse]

+Alexis Trodglen Hope you enjoy it!

[@maximusdizon7267]

you were what??? whating...ok well then ...😑

[@Brandyalla]

+Master Max JEDI Maybe it's shorthand for "waiting for whales"

[@maximusdizon7267]

OK I didn't know that lol

[@tennicktenstyl]

Didn't understand anything, sugar still gathers in the center of my tea cup.

[@HaydenHatTrick]

That would be due to centripetal motion (a force going towards the center of rotation). The only difference is that the system is more complex.

[@samsonclement7604]

When you stir the cup, water is forced outward because of centrifugal force, the same sensation you get when riding a carousel. This makes the pressure higher towards the edge of the cup. Close to the bottom of the cup friction between the fluid and the cup forces the swirling motion of the water to slow down and this in turn makes it possible for the pressure difference to establish a current towards the center of the cup that is stronger than the centrifugal force.

[@yeet6764]

@@samsonclement7604 I thought she said centrifugal force doesn't exist

[@davidsweeney111]

In classical mechanics, a reactive centrifugal force forms part of an action-reaction pair with a centripetal force.

[@MauricioMartinez0707]

You see that sounds right but everyone keeps saying it doesn't exist. But yes in my head it's similar to the normal force

[@MrSun-gk5kl]

I'm studying for my senior year physics exam so I'm no expert but I'm 99.99% sure this vid is correct on the centrifugal force being a fictitious force

[@mjsaedy6637]

Not true, the action/reaction pair do *not* affect the same object: the centripetal force applied to the object is the tension force from the string, the object exerts a reaction force *on the string* , this reaction force has no interest to us since we are studying the rotating object not the string. To realize why the Centrifugal force is not real, just examine what happens when we cut the string: there is no more Centripetal force so the object moves along a straight line that is a tangent to the circle (in the direction of the Velocity at the moment the string was cut). If there where an actual Centrifugal force, the object should have moved in a straight radial line *perpendicular to the tangent* , which is not what happens in real life.

[@onglinwei2418]

Centripetal force is actually a resultant force so there's no centrifugal

[@franksmith9027]

@@mjsaedy6637 You say:"Not true, the action/reaction pair do not affect the same object:" Of course they don't, if they did they would cancel each other out. When you swing a ball on a string your hand exert a centripetal force on the ball which reacts by exerting a centrifugal force on your hand and it is obvious these forces pass through the string. You thus have an action/reaction force pair that obeys Newton's Third Law.

[@Malfunct1onM1ke]

Hooray for the guy who ends up cleaning up all the vomit \ o /

[@IceMetalPunk]

Uniform circular motion is fun. Rotational dynamics, though...I could never get my head around that. I understood relativity perfectly fine, but as soon as we started discussing torque, I was so lost. It didn't help that I had a professor whose answer to "where did that equation come from" was just to write more equations on the board with little to no added explanation...

[@joekenyon1599]

that's been my teacher pretty much all year lol.

[@lema1425]

after having no idea what’s been going on in physics for a week and having a test on this tomorrow, it just made complete sense.

[@TheRealADHDavid]

Dr. Shuster is a teacher at my High-school :D

[@rileypurcell2159]

?

[@MIQofDMC]

+Riley Purcell 9:39 consultant - Dr. David Schuster

[@rileypurcell2159]

+MIQofDMC Oooohhhh. Lucky you!

[@rohitreddy6794]

Best channel for physics

[@alexjordan8838]

I love physics and all, but her voice is beautiful

[@MusiCaninesTheMusicalDogs]

And so are her eyes.

[@Ray-ye8gz]

Honestly, those physics videos are really helping me out! In fact, A lot :-)But you need to repeat the video and focus a lot on what Shini is saying.

[@12Rman21]

did you just squeeze in dimension analysis at the end there? That might deserve a little more attention since it's a super usefull tool for checking any calculation you are doing. And it gets only more important the more complicated your equations get.

[@robinhooper7702]

There is one thing I am not able to understand and that is speed and distance traveled in a circular motion, in the sense I'm to convey here. Take the second hand of a clock as reference. Measure from the outermost point of the second hand and the distance it travels in one minute, and now measure the distance of the innermost point, from the same second hand. The distance traveled will be very much different to each other, but it takes the same amount of time to completely travel in a complete circle returning to its' starting point. So, you can see that the distance traveled by the innermost point must be traveling very much slower because it cover less distance in the same amount of time. I just don't get it. I thank you all, in advance, for your feedback.

[@olizelda]

GREAT! I did you little key demonstration in my backyard, and now I've LOST my HOUSE KEY in the grass!!

[@rmatkins16]

I'm so glad they've sorted out the heights of the lights behind her, it's all my brain could focus on before!

[@lukasdanarm]

This so helped me. I have a circular motion test in physics tomorrow and this really saved me.

[@josephmontoya942]

glad these videos are clearer now

[@ashutoshkumawat3690]

Your eye contact is appreciable along with your stuff...it kept me focussed.

[@eichi7618]

Ahh, wish these physics topics were already finished lol, woudve helped so so much in my physics exam just like how much it has helped me in bio and chem! Found the biology 8402 igcse paper 1 so easy mostly because of CrashCourse!

[@AhmadAli-sh1xv]

She really has a clear way of explanation compared to a lecture but i feel that is from the fact that she has the time and the ability to use accurate graphics, though I also think that is why she could go at such a quick pace, though that also makes me want to see more calculus in the show, you know introduce the basic parts then get more technical and mathematical. Though maybe I am asking for too much. although I am using although and though to much.

[@wingedlionn]

screaming if i had seen this video a week ago i wouldnt have failed my physics a level lmao

[@LagMar100]

Overall great video and examples! thank you CC team! :)

[@daroastftw7579]

Thank you so much! In our intro to uniform circular motion, we rushed through some derivations, and the concept wasn't really explained. Thank you for putting words to variables and numbers!

[@Jewboyjacob]

WTF!!! A thought y'all had this whole physics series!!! My Physics Exams Tomorrow!!

[@mosajid7861]

Same but my exams in an hour

[@shoeeey5319]

I love these videos, they're so useful for my exams! thank you!

[@arjunabraham9035]

These videos would have been so useful on Monday.

[@caitlynemily892]

honestly these videos are the only thing saving my ap physics grade

[@ynnna21]

Increase speed along circular path or decrease the radius results in higher acc

[@alberttorres4830]

That g-constant acceleration of Earth is the differential of the two circular motions of Earth. Vo=velocity of orbit : Vr=velocity of rotation. So: (Vo/(Vr × g))=d-constant'the rate the Sun's pull stoops or deviates to Earth's center to create g. (Vo/(Vr × d))=g-constant'free-fall.

[@IceCreamMilkshake777]

oh yeah and please do momentum and angular velocity and angular momentum pleaseeeeeeee

[@liz_3d]

5:10 Isn't this simply Newton's Third Law though ? The ride itself pushes against you so your body has an equal opposite force, this is the force that you feel pushing you against the wall...

[@febijaimon7466]

+Lizgony That's what I was thinking

[@FHCPhysicsAcademy]

Well, Newton's 3rd Law occurs between 2 objects. Yes. The wall pushes against you while you push against the wall - the 3rd Law. But what's pushing YOU against the wall? Nothing, really. You would move in a straight line - if not for the wall pushing you toward the centre of the ride. This is why that outward force is deemed fictitious.

[@__nog642]

When you are spinning, the ride itself (the seat you're sitting on) is connected to the center, and it experiences tension force as centripetal force. You, however, aren't directly connected to the center of the ride so there is no tension force pulling you inwards. Your inertia makes you move in a straight line tangent to the circle. However, the wall of the ride is in the way, and exerts an equal and opposite force on your body, keeping you from going in a straight line, and that normal force is centripetal force for you. So basically what you feel isn't normal force, it's your inertia. Normal force is what's keeping you on the circular path.

[@liz_3d]

Neil, my friend, you deserve a cookie ! Nay! Make that TWO cookies ! :D

[@OP_-pk9hm]

Lizgony No sir that's the misconception about centripetal force it doesn't exist. It feels like it but the ride isn't the reason for flying off or feeling pressed.

[@marvcyclone4167]

got a test next period, wish me luck

[@sidrabarry1921]

These are so great to watch after going through text! Great way to reinforce the information, thank you!

[@rakshaaiyappan8193]

Hey there, thank you guys for these awesome videos!

[@leopoldopascuaii3007]

Thank you Crash Course Physics.

[@jennihaataja932]

"So engineers tested potential astronauts by putting them in a human centipede."

[@AStrangeTree]

I've taken Calc, but not physics. Sometimes it's hard to wrap my head around what they're saying, I have to make sure to pay attention and visualize a lot in my head, rewinding from time to time, but in the end, it's nice to come away with a little better understanding than I had.

[@TheTrueTeX1]

Love the fact, that you took Link for the depiction! :D

[@artofthescreenshot2574]

Physics aside the intro is LIT. Love this channel.

[@FHCPhysicsAcademy]

It's important to remember that the centripetal force is really not a force in and of itself either. It's the NET force once you consider the vector sum of all the forces acting on an object moving uniformly along a circular path. Remember that, in Newtonian dynamics, it's the net force that causes an object to accelerate. Since the acceleration is centripetal, it would follow that this acceleration is directly associated with the centripetally acting NET force. Y'know?

[@rkpetry]

Sidebar note: Years ago NASA put together a Course on nomenclature (how to know what scientists are saying) and the curator included the common physics term, jerk, the change in acceleration, but, I pointed to this very example where uniform change in acceleration is 'swing' not 'jerk,' (Pump, don't jerk the swing)... Centrifugal is not the only pseudo-moment.

[@MrJonathanStag]

So is the centripital force akin to the normal force in that inertia is pulling the object away from the center, but centripital force is pulling it in similar to how pushing on a table puts an equal force on your hand?

[@MartinPereira-qn2mt]

so then earth radius = 6300000 m and acceleration is 9.8 m/s, if we want to orbit earth it would be 9.8=v²/6300000 v=7858 m/s or 28286 km/h or 17576 mph (at sea level)

[@Brandyalla]

+Martin Pereira howthingsfly.si.edu/ask-an-explainer/do-all-satellites-have-fly-same-speed-so-not-leave-their-orbit "The International Space Station has a Low Earth Orbit, about 400 kilometers (250 miles) above the earth's surface. Objects orbiting at that altitude travel about 28,000 kilometers per hour (17,500 miles per hour)." =applause=

[@guddysingh8072]

A spaceman in training is rotated in a seat at the end of the horizontal arm of length 5 metre. If he can withstand accelerations upto 9 g, then what is the maximum number of revolutions per second permissible? (Take g = 10 ms^-2) (A) 15.5 rev/s (B) 1.35 rev/s (C) 0.675 rev/s (D) 6.75 rev/s

[@spencerwadsworth913]

'Centrifugal force' actually does exist. It is called fictitious because the rotating reference frame is not inertial. However the tendency of objects in a rotating reference frame to accelerate radially outwards , which is what we are calling 'centrifugal force' is very real. It isn't technically a 'force', because 'radially outwards' is not a valid vector direction in a rotating reference frame, but the phenomenon still exists, and from the rotating reference frame, it behaves exactly as a force does.

[@luismartinez-ue4fv]

if the teachers of the world give the classes like this video, i would never miss one. Love CrashCourse

[@davidconnolly1130]

My physics mark: brought to you in part by Crash Course Physics

[@ashleya1601]

We're just about to start this in class, HELPED SOOO MUCH!!!

[@echodots]

I swear I had to replay this one 4 times just to figure out what was the difference between the analogy of the car versus the key lol. I love watching things that make me go grab a pen lol.

[@PragmaticCulture]

Crash Course for the win helping me study for physics.

[@benth162]

I am very please to see a woman explaining things that used to be mainly in the domain of men. Very well done young lady, my hat is off to you. BRAVO !