Basic science question...

[[xeno]Julios]

The basic idea as far as I understand it is that the classical vector addition theorem is wrong. It works for most practical purposes, but it isnt 100% correct. And the larger the numbers you're dealing with, the more off you get.

In other words, any time you want to combine (for lack of a better term) two velocities, you can't just add them up. Two velocities cannot simply be added together. An explanation below is provided.

interesting. So in reality, he was still moving 3/4 of c with respect to train right?

[Chupacabra]

right

[Chupacabra]

Ahhh, I was wondering when the first physics-knowledgeable person would appear.

he is the one that asked the question at the beginning of this thread!

referring to me?

i'm not a physics guy. my dad is a physicist and recommended to me gamow's book so i've been flipping through it

[[xeno]Julios]

Ahhh, I was wondering when the first physics-knowledgeable person would appear.

he is the one that asked the question at the beginning of this thread!

referring to me?

i'm not a physics guy. my dad is a physicist and recommended to me gamow's book so i've been flipping through it

what i meant was that it seemed that hax thought you were physics-knowledgeable based on the fact that you answered the "riddle".

But i pointed out to him that you were the one that posed the riddle in the first place.

(of course, this does not mean you are not physics-knowledgeable)

[Chupacabra]

oh lol

[Nightshade]

yea, but doing the limit of 1/x as x--> infinity is not quite the same as just dividing by infinity is it?

Correct, because what you're doing is finding a bounding value that the function approaches as x infinity, not right AT infinity. Whatever that would mean.

[Nightshade]

By the way, I really think that you need to be in mechanical engineering to do this sort of physics, since its not in any of the obligatory science courses at my school, I'm taking a "Physics For Engineers" optional course (gotta take 3 optional courses) and because of this course I've decided not to go into engineering in university

No, you don't need to be in an ME program. That material is covered in a first semester physics course.

Why didn't anyone here think about it then?

Because not everyone here that's taken physics has perfect recall. Doesn't mean that you need to be studying mechanical engineering to study basic physics.

[[xeno]Julios]

ok so would it make sense to say that the proportion of the sphere in contact with surface would be that very bounding value?

or can you not apply that sort of value as a "quantifier"?

[Geebs]

No, you don't need to be in an ME program. That material is covered in a first semester physics course.

Why didn't anyone here think about it then?

Because not everyone here that's taken physics has perfect recall. Doesn't mean that you need to be studying mechanical engineering to study basic physics.

Too damn right, I've completely forgotten most of my mechanics.

You couldn't quickly remind me why gravity's exerting torque in this situation? Is it due to centre of gravity being r away from point of contact with slope?

[Nightshade]

Recall: Torque = radius X force applied (that's a vector cross product).

[menkent]

did anyone ever answer the original question? you just have to keep in mind that from the point of view of the asshole leaning against the lamppost the train will appear to have vastly contracted in length. so once you've readjusted the velocity taking into account the contracted distance, <i>then</i> you can do your vector addition.
a more ammusing thought experiment that involves the same part of special relativity is this: a guy is standing on top of a train that's travelling at relativistic speed when lightning strikes both ends of the train as it passes someone outside his frame. the guy on top of the train sees the strikes as simultaneous (one rather more blue than the other, i'd imagine), but the person stationary with respect to the train sees the lightning hit the back of the train before it hits the front of the train.

edit: fuck, Chupacabra already bothered to google for the actual equations. carry on. :icon10:

[menkent]

Too damn right, I've completely forgotten most of my mechanics.

You couldn't quickly remind me why gravity's exerting torque in this situation? Is it due to centre of gravity being r away from point of contact with slope?

i'm not sure gravity is exerting the torque itself... but it's basically because the slope isn't level so you get some component of the force from gravity or friction or whatever parallel to the surface (ie- perpendicular to the radius) that causes a non-zero crossproduct.

[MidnightQ4]

Anyone else wanna try to explain this?

I didn't read the rest of this thread, but the inertia of the sphere is lowest so it can actually accellerate fastest due to gravity (i.e. there is less turning resistance to its rest state because more of it's mass is closer to the center.) The ring should be the slowest, as it's mass is at the outside, farthest from the center, giving the highest inertia.

So tell me, amiright?

[menkent]

So tell me, amiright?

basically, yes.

[Guest]

Anyone else wanna try to explain this?

I didn't read the rest of this thread, but the inertia of the sphere is lowest so it can actually accellerate fastest due to gravity (i.e. there is less turning resistance to its rest state because more of it's mass is closer to the center.) The ring should be the slowest, as it's mass is at the outside, farthest from the center, giving the highest inertia.

So tell me, amiright?

Yes, you're exactly right. I've explained it all though, so if you didn't read what I've explained, then congratulations, you're the first person to get it.

[MidnightQ4]

cool, ya I didn't read your explination, but I did pay attention in physics class

[tnf]

this thread has done nothing but remind me that i've forgotten too much about physics.

I took 1.5 years of calc based physics in college, and a statics class and some astrophysics crap (but I was a biology/chem major), and I've covered all of the math involved in both the first and the following questions in this thread. but i'll be damned if the shit came to me right off the bat. re-reading all of the posts here is now making all sorts of dim light bulbs in the far reaches of my head start to flicker again....

if i had been teaching AP physics i would have been able to answer this. heh.

[Guest]

What does AP stand for? I know its advanced, but I don't understand what the acronym means.

[tnf]

advanced placement. students take them to prepare for AP tests that will give them college credit (depending on how well they do) in the specific subject.

[Guest]

oh, so all the geeks take it?

[tnf]

no. athletes, geeks, people who want good looking college applications.

[Guest]

I see. I wonder what I would be like if I lived in the US. I'd probably be on a football team in highschool trying to get a college scholarship and dating cheerleaders. Oh well, instead I'm here.

[Nightshade]

No, I can say with almost absolute certainty that you wouldn't.

[Guest]

No, I can say with almost absolute certainty that you wouldn't.

You've never seen me. If I actually was into sports, I would be pretty good.

[tnf]

i hear that a lot from people who arent into sports.

thinking back to the glory days of high school football and basketball, i recall seeing that attitude in guys who figured they should turn out. they'd show up the first day of practice with all the confidence in the world (because they knew they were good due to their performance in pick-up games and whatnot) and leave crushed after a practice because the level of play and competition was so far beyond what they were used to...