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| Thread ID: 88253 | 2008-03-21 01:01:00 | Physics Question... | John W (523) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 651236 | 2008-03-22 22:55:00 | These deceptively simple questions....of course the plane will fly.... At school, I used to hate these sort of questions in applied maths where they used to talk about ideal this, or perfect that, and the problem either bore little resemblance to real life, and real effects were glossed over or not even mentioned. It was not until later when when deeply immersed in the analytical design of real life hydro-mechanical systems, servo systems, jet engines, etc that so-called school level "applied maths" started to make sense, but perhaps we were not taught too well. Anyway, as TGoddard says, it all depends...... 1.Friction... consider that if there was no friction, would the ball roll at all, or would it just slide??? Also if there was no friction would the ball ever stop at all??? 2.Consider, a sphere touches a plane at a point, the point has no area, therefore if the ball has weight, the contact stress may be infinite, or is it ? So now the physics of contact stresses, or 'Hertzian Stress' have to be considered. The surfaces deform and work will be done deforming the surfaces, bringing into consideration the properties of the materials such as the elastic modulii and internal damping. 3.More on friction... If the ball and incline are in a fluid medium, either a gas or a liquid, then there will be resistance to motion. If the ball does rotate, or even if it just slides, fluid will be entrapped to a greater or lesser extent between the ball and the plane. The fluid will act as a lubricant, hence the physics of lubrication of bodies in contact come into play.... "hydrodynamic lubrication" and "elastohydrodynamic lubrication". I expect there are a lot of other considerations too :rolleyes: Wow, had to put my joint aside and give a 60's reply to this one..."Heavy man" Ken (No :hippie: emoticon) |
kenj (9738) | ||
| 651237 | 2008-03-23 07:27:00 | I suppose the question comes down to one of : does the ball reach the end of the ramp at the same time for both ramps? If so, the ball on the curved ramp will have a higher exit speed and therefore more momentum given it travelled a greater distance over the same time period. If the ball on the curved ramp reaches the other end first then again it has the higher speed and momentum. It will depend on the shape of the curve but my money is on the ball that is on the curved ramp travels further. | andrew93 (249) | ||
| 651238 | 2008-03-23 11:46:00 | conservation of energy says that the ball will have the same energy from falling x distance no-matter what shape the ramp was - but only in an *ideal* situation of no friction etc etc as Terry P so comprehensively put. so without friction the balls will never stop. with rolling resistance only, the longer (curved) ramp loses. with the sudden jolt at the base of the straight ramp though, you'd have to consider all sorts of things. |
motorbyclist (188) | ||
| 651239 | 2008-03-23 12:13:00 | Wow, had to put my joint aside and give a 60's reply to this one..."Heavy man" Ken (No :hippie: emoticon) I am not really sure but I do know that my left ball is lower than my right ball. The friction usually arrives slightly higher I hope. I have not tested the ramp at this time. Where do I get one at this time of night? |
Sweep (90) | ||
| 651240 | 2008-03-23 18:47:00 | I am not really sure but I do know that my left ball is lower than my right ball. The friction usually arrives slightly higher I hope. I have not tested the ramp at this time. Where do I get one at this time of night? :lol: :lol: :lol: |
kenj (9738) | ||
| 651241 | 2008-03-23 20:33:00 | conservation of energy says that the ball will have the same energy from falling x distance no-matter what shape the ramp was - but only in an *ideal* situation of no friction etc etc as Terry P so comprehensively put. so without friction the balls will never stop. with rolling resistance only, the longer (curved) ramp loses. The inclined ramp will have a constant acceleration and an easy calculated exit speed. The curved ramp will have a higher initial acceleration which will reduce as the ball traverses the ramp. Whether this results in a higher exit speed remains to be seen. Check this out : the ball travelling the shorter distance does not necessarily get to the end-point first (see part 2) : tycphysics.org Counter-intuitive but maybe the same concept applies here... Andrew |
andrew93 (249) | ||
| 651242 | 2008-03-24 04:43:00 | Force=mass x acceleration. The acceleration due to the gravity is 981cm/sec/sec. someone else can do the calculation, but I anticipate that the balls will finish equally distant from the start point as they will have identical mass and acceleration as they are falling the same vertical height. :D | Richard (739) | ||
| 651243 | 2008-03-24 10:36:00 | The inclined ramp will have a constant acceleration and an easy calculated exit speed. The curved ramp will have a higher initial acceleration which will reduce as the ball traverses the ramp. Whether this results in a higher exit speed remains to be seen. Check this out : the ball travelling the shorter distance does not necessarily get to the end-point first (see part 2) : tycphysics.org Counter-intuitive but maybe the same concept applies here... which example? that race with the dip is a completely different scenario. ok, assuming both ramps are firctionless etc etc, the identical balls falling identical heights must have the same kinetic energy, and provided they do not spin/roll, will be travelling at the same speeds upon exit of the ramps, however, this doesn't mean to say they will leave the ramps at the same times. if there is friction to make them roll, the rotational inertia etc will come into play and the geometry of the ramps will be an issue - BUT, we could still figure it out Force=mass x acceleration. The acceleration due to the gravity is 981cm/sec/sec. someone else can do the calculation, but I anticipate that the balls will finish equally distant from the start point as they will have identical mass and acceleration as they are falling the same vertical height. :D yes, but for whoever does the calculations, PLEASE use SI units:dogeye: it makes things so much easier |
motorbyclist (188) | ||
| 651244 | 2008-03-24 21:06:00 | Sorry about that motorbyclist. I went to school too many years ago. :blush: | Richard (739) | ||
| 651245 | 2008-03-25 03:03:00 | yes, but for whoever does the calculations, PLEASE use SI units:dogeye: it makes things so much easier Wow! The accolades! The pomp! The Fame! The notoriety! The Autographs I can sign! . . . and to think that you requested that they use SJ units!!!! Thanks! :clap :banana :thumbs: |
SurferJoe46 (51) | ||
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