@123 Conservation of energy and momentum is enough to solve an elastic collision easily but it's pretty hard to get the result just from Newton's laws directly.
@ACuriousMind Reminds me of a question in a high school assignment where I spent a really long time messing with the math to try and solve some problem about like a trapeze artist or something. Turns out it was like a 3 line answer when you used energy and not just forces and for some reason I just got laser focused on the wrong way to solve it.
@ACuriousMind Ookay.. Why inelastic collision energy is not conserved (may be loss of energy by producing heat or changing shape of object) but how momentum conserved?
@Azmuth : I've read hundreds of old papers. Some I think are great, some I think are awful. For example, I'm a big fan of Einstein, but I'm not a fan of Penrose.
For Integral you shared. We need mass, resultant of forces $\vec{F}(x)$ , velocity $\vec{v}(x)$ between two points. this is the requirement to solve the problem.
@JackRod Don't remember exactly, but it had something to do with height and velocity, and for some reason I tried to solve like generic dynamics for it. I'm not even sure if there was enough information for it, and I just got sucked in trying to derive all the information I needed.
for newton's second law we need acceleration and mass. What is the problem solving according to second law? What is mostly unknown/problematic parameter here
@Azmuth : yes, I've read the original paper on the EPR. I think it stinks. I'm reading it saying to myself: Albert, what are you doing getting mixed up with garbage like this!
@JackRod No I just mean like I was trying to use the information I had to figure out the last piece of information I thought I needed to solve it, when instead you didn't have to do any of that and use energy instead.
@Azmuth : read the paper by Winterberg, and also read the 1939 "black hole" paper by Einstein, (pdfs.semanticscholar.org/8dd0/…) and there's something that ought to jump out at you.
@Azmuth : It will take you too long, and I will have to go soon. So here's a clue. This is what Einstein said about the event horizon. There's something wrong with it: "This means that a clock kept at this place would go at the rate zero. Further it is easy to show that both light rays and material particles take an infinitely long time (measured in “coordinate time”) in order to reach the point r = μ/2 when originating from a point r > μ/2”.
@123 Try solving questions. We usually use energy when the path of the object is complicated enough, introducing energy concepts makes things easier. Try solving questions.
@123 : you should read about the mass-energy relation: en.wikipedia.org/wiki/… . Gravity converts potential energy into kinetic energy, which is then dissipated, and then you're left with a mass deficit. That means the gravitational potential energy is mass-energy. Then if you read Einstein's E=mc² paper you will reason that mass-energy is internal kinetic energy. So gravity converts internal energy into external kinetic energy.
Can someone here tell me that when a pendulum is tied to the ceiling of an accelerating car does the Bob remain at its place due to inertia and rest of the string goes with the car ?
@Azmuth Okayie.. I there any GooD Book to read work energy theorem which explains my problems related to me in the topic. So, i can further consult with that.
I read Kleppner Kolenkow it was super nice to read.
If we know the Force as a function of position. We can easily determine the path.
K&K explain how to view work-energy as arising from forces we know are position-dependent and have no idea how it's time-dependence is, another book that stresses this is Symon
if I place a sandwich on my left side and a glass of water on my right side, they don t seem to be attracted, as they don t move towards each other (like eg magnets)
If you're surprised that galaxies aren't just balls of matter, remember that satellites orbit the Earth and remain there indefinitely even though there is a force between them and the Earth. (ignoring atmospheric stuff slowing them down)
OK, I think I can just summarize this as: "Yes, there is such a thing as gravitational force but you barely notice it because it is so small. You would see it in a theoretical vacuum room with no frictional force and no earth, because then the two inert masses you placed in it would just move towards each other. If you d have a room of vacuum on earth you d still not see much because the gravitational force towards earth would be much larger than your 2 objects amongst each other"
It's still barely any force regardless of if Earth was there. They would slowly accelerate towards each other; but it wouldn't even be noticeable for awhile assuming we aren't talking quite massive objects.
@JMac If you two heavier objects each 1000Kg and placed carefully horizontal on the surface as lift with up with air jet you will definitely see attraction between them.
@Charlie But can t yiou say that the two masses would be attracted muuch more to the eart than to each other due to the earths mass? Which is why with the earth's presence you d barely see anything
@traducerad Your first statement is correct, the force between the objects and the Earth would be much larger (assuming they are a lot less massive than the Earth) but it does not then follow that you would see barely anything.
If you just let the masses drop towards the Earth and they hit the floor that would of course stop them from moving towards each other due to friction. But the presence of the Earth underneath them doesn't make the force of gravity between them any weaker.
@123 But with such large masses the acceleration between them is also small, even if they are somehow extremely close together. I don't think you would notice 0.00000667 m/s^2 of acceleration even if you somehow had a device that could make two 100,000 kg frictionless and 1m apart
@123 I'm talking about your comment "If you two heavier objects each 1000Kg and placed carefully horizontal on the surface as lift with up with air jet you will definitely see attraction between them." Which you then corrected to 100,000 kg. Even with those masses, you wouldn't notice the acceleration even if you got them 1m apart...
@123 If you somehow had two 1,000,000 kg masses 1 m apart (not sure how you could get them that close) acceleration between them is 0.0000667 m/s^2, you likely wouldn't notice the acceleration even in that impossible scenario. I think you're forgetting the more massive the objects, the less the force accelerates them.
For instance take a sniper that wants to hit a target at 10km, he will see his bullet deviate because the earth and his target moved while the bullet was flying
but no additional/new forces actually acted on the bullet
In my opinion don't check gravitation with heavier masses it could be fatal for earth and moon :p :)) . Try careful and intelligent experiment with smaller masses which could be possible to do.
@123 The way they did it back in the day involved just looking at the movement of planets around us, thankfully you don't have to actually make them smash together to understand the forces at play
@traducerad Well they are both pseudo-forces, yet they typically get called a "force" in physics; and it's generally just understood (and often stressed for centrifugal force) that it's an effect of non-inertial reference frames and not an actual force
@traducerad Inertia. To someone watching from outside, physics says you should keep moving straight forward with the same velocity unless a force stops you. The feel of being pushed away from the circle is really the force pushing in to keep the movement circular instead of allowing it to go in a straight line.
To someone standing watching you on the carousel there is no outwards force. The outwards force you feel is "fictitious" in the sense that you only observe it when you're in the non-inertial frame of reference riding on the carousel.
To put it another way, the actual force is centripetal force for a non-rotating observer; when you're spinning in the circle, that force pushing you in a circular direction feels like you're being pushed back instead, due to the spinning frame.
In a similar way, if you're sitting in a car and a large force is applied to push the car forward, you (a passenger) feel as though you're actually being pushed backwards into your seat, even though the only external force being applied is in the direction of travel of the car.
A big reason it feels so different is because when you're spinning, you're always facing the same direction relative to the circle, so the force always acts on the same part of you; while to an observer, the force is constantly changing direction.
1) you sit on the carousel and spin around. In this case you do feel an actual outward force, aka centrifugal force. 2) you sit on that carouse, spin around AND throw a ball to the guy sitting in front of you on the carousel. In this case there is no force felt or whatsoever when throwing the ball. It will just follow a straight path and while flying your friend will have moved/spun a bit further. You therefor have no force here, just some sort of illusion if you are in that framce of reference
So to me centrifugal force is an actual force, Coriolis is not.
@traducerad Centrifugal force isn't an "actual" force. Just because you feel a force, doesn't make it a true force. It's because a rotating reference frame is always changing direction that gives the appearance of true forces.
Just like if you're in a car that accelerates, it feels like you're being pushed backwards; but the real force acting on you is pushing you from behind.
