Classical Physics

Does an object necessarily have to come to a stop before it can reverse it's direction? Take for example a piston attached to a connecting rod, which is attached to a crankshaft. Now--assuming that there is no side play of the piston in the cylinder, and assuming that the connecting rod would not either compress of stretch during the cycle, and assuming that this particular piston was not part of the fireing cycle, would it have to stop at the top before it started down? Remember, the crankshaft does not stop, so once the throw on the crank reaches the top of the stroke it immediately starts down pulling the piston behind it. If there is no clearance in th…

In collision, law of conservation of momentum is applied only if no external force is added. Is weight considered as an external force? I think so. Anyone tell me ?

Hello, I am just wondering, why does the stopping distance of a ball bearing start to decrease after the angle of the slope exceed 45o I really don't understand why.... Thanks.

When you throw a stone vertically it reaches a maximum height and so for an instant (I'm told) it has zero velocity. How long is this instant?

I have a question about inelastic collisions. Would a perfectly (or nearly perfect) inelastic collision be able to break an object itself or another object it touches?

http://www.earthtimes.org/articles/show/986.html http://welcome.to/cnn.com/2004mn4.html diameter 0.4 kilometer estimated mass 75 million metric tonnes estimated energy 1.4 GT (1.4 gigatons TNT) the estimated probability of a hit is only 2.2 percent and is projected for 13 April in 2029 is this of interest? the name of the asteroid is 2004 MN4 I will get some more information on it in case anyone is interested. (seems unlikely that, after further observations, it will pose a significant risk) [edit: I could not confirm the estimate of 2.2 percent and now find it dubious. the NASA website I checked seems to have revised its estimate just i…

If I throw a ball straight up into the air, is it still accelerating when its velocity is 0 (at the peak of its trajectory)? I say yes...but I just want to be sure

how does this motor work? like what repels what? whats magnetically north/south? motor from the outside: the round disk rotates remove that metal disk to reveal electronics: close up of that: the copper are making electromagnets, also notice the permament magnet at the end of each electromagnet, its small but there that metal disk: picture taken of the bottom side of it that rests on the electronics so is normally not seen... its metalic, notice the magnet running around the outside of it

How much energy would it take to dump something on the sun? So basically what does it take to bring something in lower orbit, low enough to make it eventually drop on the sun? Using other planets/moon allowed.

Ive got an electronics exam in the morning, can somebody explain to me the meaning of 'gain', in terms of transistors?

we all know lightning does not strike in straight lines, it zig-zags around.... why is this? is it because of variable composition in the air? like one part will have less resistance so it'll take a d-tour via that part or what? if that was the case surely the additional distance travelled would counteract this lower resistance and thus remove the advantage of the taking that route? (once i get an answer to that i've got a question on sparks too!)

firstly the title is not the 'whole picutre' ! as a slight side-track from the Motor Physics thread, i wondered how a single magnet could have varying polarities. like i understand the phsyics of a normal bar magnet, but in this case we have a bar magnet (in a circular shape) which goes 'north, south, north, south' 4 times, resulting in 8N + 8S so a total of 16N+S (where N = north and S = south!). so if you look in this image: you can see the magnet i am referring to running around the outside of the metal 'disc'. if you take a normal bar magnet labelled N and S and take one end, e.g. N and run it around the outter circular magnet it is attracted/repell…

Can anyone offer a reason why the force due to gravity decreases as the inverse square of a distance as opposed to some other function. For instance, sound waves propogate in a spherical manor, thus sound intensity decreases as a function of the surface area associated with that sphere. The gravitational field extends in a kind of "infinate sphere" so it seems reasonable that force due to gravity might decrease in a similar fassion but it doesn't. Why?

what does the Break mean in BHP?

Yeah, I've just had my first lessons in kinetic energy (Newtonian mechanics) at high school some time ago. However, quite soon I noticed that for a massless object going at c, the kinetic energy is 0. And so, I went "aha, so that's why you don't need to kick photons around to make them move". However, this made me think: how come photons have energy then? Is it only proportional to the wavelength, and if someone tells you the wavelength of a photon you can tell the energy in it right away? Or should I just go and use ONLY the relativistic mech. way to calculate Ek and get a correct result, as I have no idea how to do it. )

I have a question about the physical interaction of objects (not physical properties, but forces that move thing), what do we call that? Also, what does the third law of motion (action-reaction) have to do with the earth, a wall, a floor, a table and moving through a medium (like air)?

Problem of the week: I have a marble that is immersed in water. Volume of the marble is 10cm^3, its density is 1g/cm^3, and of course the acceleration due to gravity is 9.8m/s^2. 1)Find the Net force acting on the marble?

I was wondering if anyone had any information about the forces in a car crash at different speeds. I am also looking to find info about how much force opposing magnets can have on each other. I am trying to figure out how big of a magnet you would need to have in two cars if they crashed to signifigantly increase the chance of survival... I know it sounds crazy, but we get a lot of points for creativity in this project

I'm having problems understanding this question, particularly part B. Any hints to send me in the right direction or explanations on the proper method to solve would be appreciated. My textbook doesn't seem to have an example quite like this one.

Hi, I am new here and I have a question. It's about speed, motion and light. When you pick up something, a bottle for example, and you shake it back and forth quickly, it is harder to see because it is moving quickly/with blurs. Why does it do that? What is that called? Does it have to do with turbulence? And would this work in a vacuum (or some similar thing)?

INSULTINGLY STUPID MOVIE PHYSICS Haha, some people have way too much time

What's a atomic clock? I heard that there are radium in them. And it's very precise

An interesting question popped up in a conversation the other day. Would the centripetal (centrifugal) force experienced near the equator caused by the rotation of the earth slightly counteract gravity and make you and everything else feel lighter? And also make you feel heavier nearer the poles? Its been a long time since I studied physics for my A-levels and I've forgotten most the equations. I know that velocity at the equator is around 1000 mph which is high but angular velocity is relatively low. I cant remember which of these is the more impotant factor. If you are lighter at the equator,does this cause any other interesting effects? such as people living at the equ…

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Hello everyone... Sound propagates in air at 340m/s by the sucessive compression/expansion of the highly compresible gas medium due to soundwaves; ¿ How do solids propagate sound with such diminished compressibility ? ¿ What is the typical range of sound progagation speed in plain soils ? Much faster ? And further ? and with less attenuation ? ¿ Are earthquakes detected by microphony or motion transducers or both ? There was once a web site and group dedicated to sense underground noises, I would appreciate any clues to locate it. Thanks, Miguel