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    Jake0024

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    [–] Motorola phone 'brazen copy' of iPhone X Jake0024 -1 points ago in gadgets

    If it sells, it doesn't matter how stupid it is. Everyone will flock to what consumers buy, regardless of how objectively awful it is.

    [–] Checking the map in 3rd lane. (140km/h) Jake0024 1 points ago in IdiotsInCars

    Literally only thoughts about themselves and absolutely nothing about the world around them.

    [–] [USA] [OH] Police speed trap caught me on my bike Jake0024 1 points ago in Roadcam

    But you can get pulled over for riding a bike drunk, even if it has no engine.

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    I know it's the same law being applied in two very similar ways--that's why I compared them. The bike wheel in a chair and spinning figure skater are so similar they are almost always taught together as two examples of the same principle. They're pretty much the canonical demonstrations used in physics classes to teach conservation of angular momentum in every textbook, classroom, and curriculum, from years of pedagogical research around the world.

    Both the figure skater and the person holding the bike wheel are changing angular speed--because both are changing the distribution of mass and need to conserve angular momentum.

    A person on a bike turning a corner doesn't demonstrate those same principles at all. It would be a more appropriate example for teaching friction in 2-D kinematics.

    [–] Democrats have 75% chance of retaking the US House of Representatives Jake0024 43 points ago in dataisbeautiful

    Yep, people will think that means Dems will somehow take 75% of the vote with 100% certainty and then scream bloody murder when Dems actually lose because they only got 55% of the vote.

    [–] TIL Mike Tyson's workout involved getting up at 4am for a 5-mile jog. Then he would do (cumulatively) 2000 sit-ups, 500 pushups, 500 dips, 500 shrugs and about 30 minutes of neck bridges daily. He repeated this 6 days a week. Jake0024 3 points ago in todayilearned

    Kind of a silly question. If they lived at the same time it would have been interesting, but modern athletes are much better pretty much across the board for a lot of different reasons. Look at world records in practically any sport from today vs 50 years ago vs 100 years ago. There's no comparison.

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    I used the comparison because both work by conservation of angular momentum. The angular momentum of the wheel changes (just like the angular momentum in the figure skater's limbs changes), which causes a change in the person/stool's angular momentum in order to conserve total momentum.

    Discussion of forces is unnecessary to explaining the end result when you just simplify the problem by looking at conservation of angular momentum. That's why the comparison to a bike turning a corner is ineffective. Yes there are obviously forces at play, but all they do is explain how the angular momentum is transferred from the bike wheel to the person. The end result is the same even if you treat the forces as a black box.

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    That's the exact same thing I said.

    It's unnecessarily confusing to mention forces. Yes, that's obviously how the momentum is transferred to make him spin, but the end result is the same if you just look at momentum conservation.

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    If it started horizontal (with "brakes open" for the stool so he's stationary until the wheel is spun up) and he flipped it upright, he would spin. If he flipped it over completely so it was spinning horizontally again (with his other arm on top), then he'd be spinning twice as fast.

    That's necessary to conserve the total angular momentum.

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    Which half did you understand

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    I believe your "correction" says the same thing I said originally. Perhaps you should reread it?

    when they pull in their limbs they aren’t spinning as far, they have to spin faster to conserve momentum.

    Angular momentum is I*w, and since I (rotational inertia) is decreasing, w (rotational velocity) must increase. So as I said, the figure skater must spin faster because their body is moving over a shorter distance and momentum needs to be conserved.

    [–] What some of the planets in our Solar System look like in daylight Jake0024 1 points ago in Astronomy

    After the sun and moon, obviously, yes it's one of the brightest objects in the sky. It varies depending on orbits, sometimes it's brighter than any star, sometimes it's like #3.

    Yes, it will be in nearly the same position tomorrow (setting an hour or so after the sun). Planets change position pretty slowly from one night to the next.

    [–] Trying to hijack a car but everything backfires Jake0024 2 points ago in IdiotsInCars

    Everyone likes to imagine they're the star of an action movie I guess

    [–] What some of the planets in our Solar System look like in daylight Jake0024 10 points ago in Astronomy

    It's one of the brightest objects in the sky, so yeah it should be pretty easy to see (and you don't need binoculars)

    [–] Angular momentum Jake0024 2 points ago in BeAmazed

    In the original situation, it starts vertical (call it 0) and flips it horizontally in either direction (-1 or +1). He goes from stopped, to spinning one way, then spinning the other way.

    If he started it horizontally and flipped it over completely, it'd be like going from -1 to +1, so he'd go from stopped to spinning (twice as fast)

    [–] Angular momentum Jake0024 1 points ago in BeAmazed

    No, but he would start to spin if he turned the wheel over so it's spinning horizontally the other way (and twice as fast, since the change in momentum would be doubled versus the original situation).

    [–] Angular momentum Jake0024 218 points ago in BeAmazed

    It’s just conservation of momentum. The wheel is spinning upright, and when he turns it over, he’s making it spin level to the ground, so he has to spin the opposite way, also level to the ground, because that momentum has to come from somewhere.

    It’s the same concept as figure skaters spinning faster when they pull their arms and legs in. Momentum has to be conserved, and since when they pull in their limbs they aren’t spinning as far, they have to spin faster to conserve momentum.