Angular Momentum - Physics 101 / AP Physics 1 Review with Dianna Cowern

Lesson 15 (Angular Momentum) of Dianna's Intro Physics Class on Physics Girl. Never taken physics before? Want to learn the basics of physics? Need a review of AP Physics concepts before the exam? This course is for you!

Exercises in this video:
1. A box and a sphere are sliding and rolling, respectively, down a ramp. If they start from the same height, and we ignore friction on the box, which will reach the ground first?
What if it were a full soda can and an empty soda can?

2. A sphere of mass 4kg rolls down a ramp, starting with a height of 5 meters from the ground. How fast is the sphere rolling when it gets to the ground?

3. If every person on Earth ran around the equator in the same direction, what would their total angular momentum be? Use 65 kg as the average mass of the 7.8 billion people on Earth, and let them run at 5m/s.

4. Given 8 x 10³⁷ kg•m² as the Moment of Inertia of Earth, by how much would all those people running change the angular speed of the Earth?

Special thanks to Kari Byron for her wonderful shoutout at the end of the video! You can follow her on Twitter @KariByron and Instagram @therealkaribyron.

Credits:
Dianna Cowern - Executive Producer/Host/Writer
Jeff Brock - Lead Writer/Course Designer
Laura Chernikoff - Producer
Kaitlyn Today - Video Editor
Sophia Chen - Researcher/Writer
Erika K. Carlson - Researcher/Writer
Hope Butner - Production Assistant
Levi Butner - Videographer
Lauren Ivy - Set Design
Vanessa Hill - Consulting Producer
Aleeza McCant - Illustrator
Rachel Allen - Illustrator
Consultant - Kyle Kitzmiller
Lucy Brock, Samantha Ward - Curriculum Consultants
Cathy Cowern - Transcription

[physicsgirl]

Since the question has come up in the comments: for the ramp problem, we're turning friction off for the square, but back ON for the sphere, so it can roll. Yes you are all correct, it would not roll without friction! :) 9:58 - "And then WITH friction, the spherical cow is going to roll."

[iiserite_das_rahul_]

Probably my comment will get But I just want to say that I saw her videos which were 8 years And the way she made progress is truly From a few subscribers to 1.76M From 2 mins small experimental videos to 30 mins descriptive videos...
This is how she made her
You always deserve a 👍 from
Well keep it up .... Will wait for the next vdo

[ElectroBOOM]

HELLO! Thanks for the great course! May I make a comment about the demo of 15:20 of weird water movement (if I understood your video correctly)? The reason water seems to move forward to the motion of the water pipe is not due to increased speed of water to maintain the same angular momentum. If that was true, then in around 16:12 where the water almost curls back to the same radius it would return to the same spot too. When water leaves the pipe, water droplets start moving in a straight line and won't continue rotating with the pipe. And where they end up in a few moments related to the nozzle makes you think they went ahead, while all of them were just moving straight. An animation would explain it more clearly! So what we see is an illusion of water moving ahead of the spin while it is not. HAVE FUN!

[hakanyurtluk]

Just a little correction:
When water goes outside from the pipes and at the same time they are turning around, water will have a tangential speed to front and radial speed to the outward. Because of this reason, they will have a direction near to the front. However as it is seen in the video, they curl back. BUT! this is an illusion. Actually, they are not curled back. Just as an example let's think about not radial but the tangential speed. For a simplification we have two water particles. The first water particle will have a tangential speed when it leaves the pipe and goes forward. Then, the second water particle also goes forward but it will leave the pipe after the first one. Because pipes are turning, the second particle will leave the pipe from a further position. As the two particles just goes on a straight path, the second particle will have a path near to the front compared to first particle. As we think about all particles this way, first left particles looks behind and it seems like while the pipes are turning, water curls back.

As a result, this is the reason of illusion why water just goes on a straight path but not curls back actually.


And also in order to avoid from some misunderstood:
The pipes that has water output to the middle works in the same way. Water particles follows straight lines and as the pipes are turning, they are seems to behave like they are approaching to front and turning outside. There is no words to explaining them with using angular momentum. It is already correct. As it is mentioned in the video, angular momentum is conserved. Also, as I mentioned here, water particles will follow the straight path and they will not curl anywhere, so it is normal that there is no reason to have change in angular momentum.

So also just think about this way.

Have a nice day :)

[K_ingh]

Thank you diana for doing these science lessons, I don't need them anymore but you really help out many people with these videos.

[cagataycakirtas]

I have a question, is this course going to continue after high school material is over or are you planning to start another course including calculus and higher-level subjects?

[rahmanbikmukhametov]

The “trick” with pipes and water has even more cool physics! Try to explain the curve of the water flow from the rotating frame of view - here how you come to the non-inertial reference frame and related inertial forces

[tylerdean]

I have an AP physics test tomorrow, Im really thankful for this series as I can review a bunch of stuff that I haven't done in a while.

[aislinnswag]

this video was recommended to me out of nowhere.
I'm a freshmen who is not even able to take physics.
I'm now going to learn physics from you because I do want to take it and if I take it now I can ace it later.
big brain moves.

[migfed]

I really appreciate your effort and this is exactly the kind of stimulus that youngsters need, this is going to be key for millions of young minds to step forward and pick up a STEM career.

[umanglunia]

These videos are so well paced. Love this series!!

[roraraptor]

Thank you for sharing your knowledge with the world like this! You’re a treasure! 💖

[timothyphillips]

You got me with Rodney Mullen (Yes, I am a skater), now I've been learning physics thanks to you.Sending you a virtual high five and a big thank you from Australia.Tim ♥️s Dianna.

[Jono_Music_andstuff]

"Done being Humerus" 🦴 . Good one 🤣🤣

[taranjeet]

Hey diana, just don't stop these lessons, because I love your background😅( but your explanation is equally good)

[deepakjoshi]

The water pipe experiment is amazing! ❤❤❤👌👌👌👌

[ApolloMcDonnean]

Just found this channel. I wish there were more people like you. The world have surprisingly uneducated youth...
Best of luck.

[seanmostert]

I can’t thank you enough for sharing your wealth of knowledge and taking the time to simplify this for everyone

[trxpicalsxph]

wow i just asked alexa who her favorite youtuber is and she said u! so i decided to check out ur account and its so cool! :D

[RobertSmith-pwio]

EXCELLENT again Professor! You bent my brain from the very beginning of this video! Thank you very much.