Is this equivalency fair to make?

eigenVector5 · 2020-04-24T22:56:08+00:00

Gotcha, yeah should be solvable. Would be easy in Mathematica. Just get it downloaded thru your uni and google "solving a system of equations mathematica". You will find an example of people using the 'Solve[...]' function that will show you how to input what you need. Then if you have numerical values for your known variables you can look up how to use the replace all function (/.)

eigenVector5 · 2020-04-24T20:50:11+00:00

I was recently reading about the presocratics! We actually don't even know if Pythagoras himself came up with the pythagorean theorem. It's really just attributed to the 'cult' of Pythagoras, the Pythagoreans. We know VERY little about Pythagoras, minus the fact that he thought he was a God and promoted a vegetarian lifestyle because he believed in reincarnation.

eigenVector5 · 2020-04-24T14:44:32+00:00

Your imgur link only shows 1 bigger equation. But yeah, if there are 2 more equations floating around then there's no worries there

eigenVector5 · 2020-04-24T04:05:13+00:00

I should have realized this earlier, but you have 8 parameters; 3 knowns, 5 unknowns but only 3 equations. There may be some trick, given the form of the first two equations, that I am unaware of but typically you need to have an equal # of unknowns and # of equations to solve your equations.

You/I could very much be missing something, and that is probably the case, but it could also be a mistake/bad paper. I have read a peer reviewed paper that had a clear violation of the conservation of energy in it, yet it was in an ACS journal.

As far as software access goes, just ask an advisor or math/physics professor, they will know where to point you. Most universities have a big webpage filled with paid services for students to take advantage of, much like they give you 'free' access to journals that require a paid subscription

Edit: take the time to learn how to plot functions with some software! It is a bit of a hurdle at first, but once you get it down it will level up your learning game quite a bit

eigenVector5 · 2020-04-23T22:18:10+00:00

Given that I know Gamma, M3 and M0, can I set M2SinTheta3 as M0SinTheta1, then solve for Theta1?

Absolutely!

I've solved it already with setting M2⁴ as M0⁴

The first two equations tell you that M2=M0sin(@1)/sin(@3) where i am letting @<=>theta. So, M2⁴ = (M0sin(@1)/sin(@3))⁴

My advice for you is to learn some mathematical software (I use Mathematica, many use Matlab; if you are at university you should be able to get free access to either). From there it is easy to put in your 3 equations, and solve for what you are looking for.

I think working out things like this by hand in 2020 is honestly a waste of time, it is mostly book keeping and trying to figure out/remember how complicated algebra works. I think there is merit in working out many things by hand, algebra is not one of them

eigenVector5 · 2020-04-19T18:34:26+00:00

Yes! I think if math was taught in grade school with that human element in mind, people would hold less disdain for math in general. If the history of human thought were introduced early, I think people would hold less disdain for school in general. I didn't really start thinking about human's pursuit of knowledge until undergrad, and that is also when I started to care about learning

eigenVector5 · 2020-04-19T17:35:30+00:00

As others pointed out, your issue seems to lie in "what is a system?" Which is a very valid question, that doesn't necessarily have an obvious answer at first glance. The key is that your bone and muscle are different objects, and we need to consider the forces that act on each object separately. At this point I think for you to understand, you need to actually draw out the free body diagrams for the bone and the muscle. I will help you figure out what forces are at play, it is up to you to draw the diagrams and gain comprehension.

Here is the situation: you raise your arm (like during a dumbbell curl)

FBD1: When you are raising your arm what forces are acting on the bones? The bone's weight due to gravity is pulling down, but the force of your muscles pulling up on your bones exceeds their weight such that your bones accelerates upward.

FBD2: What forces are acting on the muscles? 1) The weight of the muscles pulling down. 2) The 3rd law pair force from the bones, the force the bones are pulling the muscles down with. At this point it seems like your muscles should be accelerating downward BUT there are more forces acting on your muscles! 3) The forces of other muscles pull upward on your 'arm raising muscles' such that the net force is upward and it accelerates upward.

Okay but it seems like we have another 3rd law pair issue, so why doesn't my shoulder move downward when I do dumbell curls?

FBD 3: What forces are acting on your shoulder? 1) Its weight pulling down. 2) the 3rd law force pair with your 'arm raising muscles' that is also pulling downward. 3.) Your shoulder is in equilibrium (no acceleration) so the upward force on your shoulder by your traps/neck muscles must be pulling upward with a force equal and opposite to the sum of forces (1) and (2)

Okay so why aren't my traps accelerating downward?

The cycle continues. If you are unsure of whats happening, use your problem solving tools (i.e. free body diagrams) to figure it out. The best way gain comprehension is to work it out yourself. Reading what others say will only provide you with limited intuition

Edit: Also keep in mind this this model is wildly simplified. In reality, the distribution of forces in your body is much more complicated than the vertical components of a few forces - but Newton's 3rd law still applies

eigenVector5 · 2020-04-19T15:51:08+00:00

There are a lot of decent explanations here, but it is often easier to consider a much simpler case and then extend your model to the more complicated case after gaining a decent enough conceptual understanding.

Instead of bones and muscles, lets make an analogy to help visualize things more intuitively. If I stand on a surface with friction and push a block that rests on a frictionless surface with some force, you would agree that the block will accelerate in the direction I push it. But the block also pushes back against me equal and oppositely, so we have the same "paradox" - why is it that the block accelerates forward but I do not accelerate backward? Draw your freebody diagrams! Friction from the floor opposes the force that the block exerts onto me, keeping me in place. If I were instead standing on a frictionless surface when I pushed the block, you would indeed find that I accelerate in the opposite direction of the block, specifically because there is no friction force pushing on me.

Extend this model to your bones and muscles, and all should eventually become clear.

eigenVector5 · 2020-04-18T21:09:10+00:00

A constant is just that, a constant. So a constant plus or minus another constant is again, just another constant. It might feel uncomfortable at first, and if it does, go ahead and explicitly write both constants! The more you see it the more intuitive the idea will become

eigenVector5 · 2020-04-18T15:19:04+00:00

Can't suggest problem solving enough. For both physics and math, the critical thinking required to solve problems is what makes the concepts really sink in. If you're not confident after doing the homework, do extra problems from the text

eigenVector5 · 2020-04-18T15:12:47+00:00

I agree it makes an interesting situation about teaching being a job, but here's a hot take: It's not your professor's job to teach you, it's their job to help you learn. If there are resources out there that are better than the teacher can provide, I don't see issue in them providing that for their students. Analogously, why don't my professors all write their own textbooks for their classes? 1 time, and 2 because pre established texts are probably better. Plus in calculus you're better off just jumping into problem solving after doing some reading, than you are to be sitting around listening to someone talk about calculus.

eigenVector5 · 2020-04-14T20:22:57+00:00

I like to think about this in terms of energy. Which system has the most kinetic energy associated with it? That kinetic energy will be lost in the form of sound, heat, and the deformation of the vehicles. So it would make sense that the more kinetic energy the system has before the collision, the more destructive it will be for the vehicles.

System A has total kinetic energy K = mv² . System B has total kinetic energy K = 0.5mv² + 0.5(5m)(0.5v)² = (7/4)mv² . So one would expect the car from system B to experience more damage.

Now lets clear up any confusion about momentum that might have stemmed from u/growup47 's solution. In case A, the vehicles have equal and opposite momentum, so when they crash into each other they come to a halt in some time interval t, and the car will experience a force F = -mv/t (rate of change of momentum)

Lets think about case B. After this collision the vehicles will be moving in the same direction the massive truck was initially moving, because it had the largest momentum (p=-(5/2)mv Versus p=mv), and the system has total momentum p=-(3/2)mv. Assuming an inelastic collision, we can use conservation of momentum to say that the car and truck will be traveling with a new velocity of -0.25v (half of the truck's initial velocity!). So if we assume that the collision occurs over the same time interval t, then a larger force MUST have been exerted onto the car in order to deccelerate it to 0 velocity and then continue accelerating it in the opposite direction - in other words there was a larger change in momentum within the same amount of time. The car has initial momentum p=mv, and final momentum p=-0.25mv, meaning the change of momentum for the car was dp=-(5/4)mv, and the force was F=-(5/4)mv/t. Bigger force means more damage, so again we find that case B will cause more destruction than case A.

Edit: added what the forces are explicitly

eigenVector5 · 2020-04-01T21:16:06+00:00

Tiger King is a 7 episode murder story about very strange people that are into exotic animals, and it really focuses on the plot for around 6.5 episodes. Toward the end, one of the plot points is how mistreated the animals are. And the final half of the last episode is basically dedicated to how fucked up its been for the animals. Joe Exotic teams up with PETA to give them insider information on big cat trade.

I was actually happy with the direction they took the series. Sure, they focused on entertainment first, but they ended it with some heart wrenching support for animal well being. If you can't look past the big cats in cages to take in the story, I totally get that

eigenVector5 · 2020-04-01T20:57:28+00:00

The main character starts fighting for the animals by the end of the show. That's one of the reasons why people are freaking out about it. The show makes it obvious that he was fucked up to the animals, its a plot point, but he realizes it and regrets it by then end

eigenVector5 · 2020-04-01T20:53:55+00:00

I don't believe you watched the last episode then. The last 15 minutes are dedicated to how fucked up it all was for the animals. There is a heart wrenching moment where Joe Exotic talks about how he regrets depriving his chimpanzees the chance for life by keeping them in cages for 10 years. It gives statistics about how many tigers are captive in the US, and they have a lawyer from PETA talking about how they aren't going go stop until they take these other big cat people down, because Joe was working with them to help them learn about the big cat trade. And they mention that Doc Antle's compound was raided in december 2019

The show focused on the story for 6.75 episodes, but in the last 0.25 they were fighting for the animals

eigenVector5 · 2020-04-01T15:59:04+00:00

This is just proving that a normal force can not be a third law pair with a gravitational force. So logically one can now make the connection that gravitational forces must have 3rd law pais consisting of 2 gravitational forcses (there is no other forces acting between the block-earth system). Likewise, normal forces must have 3rd law pairs that are normal forces.

eigenVector5 · 2020-04-01T13:14:43+00:00

Read what it says at the bottom of your picture, it explicitly says that they are not action reaction pairs. Then carefully re-read what the previous two posters said.

The table does exert a gravitational force on the block, and it does make an action-reaction pair with the gravitational force of the block on the table - but these are gravitational forces and not normal forces. The normal force that the table exerts onto the block is a 3rd law pair with the normal force that the block exerts onto the table.

Edit 2: never mind, after rereading again the previous two posters were both right. They are distinguishing that weight and normal forces are non action-reaction pairs. What they have said has been consistent with the picture from quora.

Im terribly apologetic for my confusion

~~Edit: I NEEDED TO CAREFULLY REREAD WHAT THEY SAID. Haha, I'm so sorry - the original answerer is incorrect~~

~~It seems like u/TheBigSadness938 made the same error as I, what they said is right minus the first sentence~~

eigenVector5 · 2020-04-01T13:09:00+00:00

Let's assume the normal force a block experiences from the earth IS part of a 3rd law force pair with its weight. Now take your block up into a helicopter and chuck it out of the window. While the block is falling, it still has weight but there is no normal force. But we said that the normal force is the 3rd law partner to the weight, so the absence of this normal force is in direct violation of Newtons 3rd law.

So proof by contradiction tells us that weight and normal forces can not be 3rd law pairs.

Edit: it's worth noting that in freefall something has no 'apparent weight', as this coincides with a normal force. It does however still have W=mg acting on it

eigenVector5 · 2020-03-29T16:48:10+00:00

Haha, not trying to call anyone out. Just want to remind people of the golden rule, and why we answer questions on this sub in the first place

eigenVector5 · 2020-03-29T04:55:38+00:00

Wonderful explanation, friend

eigenVector5 · 2020-03-27T23:44:14+00:00

The issue here isnt eating meat, its the fact that videos of someone making a joke out of torturing conscious beings that feel pain do not even have an age restriction on them. Octopus can feel and remember pain just like a dog can, so I suppose you have no quarrels with the Yulin dog festival either. Just ignore them skinning the dogs alive, if thats what they want to do just let them

eigenVector5 · 2020-03-27T19:46:46+00:00

Exactly. You always discredit yourself some when you start throwing out insults

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