regular_john Posted July 23, 2010 Share Posted July 23, 2010 I was never very good at physics, at all. Chemistry and biology I could handle, not physics though. Link to comment Share on other sites More sharing options...
soprano Posted July 23, 2010 Share Posted July 23, 2010 I once dropped my trousers and my birds jaw hit the floor at the same time. Thats giggity gravity. :winkold: Link to comment Share on other sites More sharing options...
CarewsEyebrowDesigner Posted July 23, 2010 Share Posted July 23, 2010 Did she just finish ironing them? Link to comment Share on other sites More sharing options...
soprano Posted July 23, 2010 Share Posted July 23, 2010 Did she just finish ironing them? No but I soon had her pressed against the wall. Link to comment Share on other sites More sharing options...
CarewsEyebrowDesigner Posted July 23, 2010 Share Posted July 23, 2010 Well played sir. Link to comment Share on other sites More sharing options...
packoman Posted July 23, 2010 Share Posted July 23, 2010 Without air resistance 2 objects the same shape would land at the same time. Things fall at the same speed, only air resistance changes it. Link to comment Share on other sites More sharing options...
mjmooney Posted July 23, 2010 VT Supporter Share Posted July 23, 2010 I am reminded of my comment in the cheating/pub quiz thread, where I drew the distinction between "the clever clogs answer", and "the pub quiz answer". The stuff about general relativity is the clever clogs answer, the "both at the same time" bit is the pub quiz answer. It's correct to all intents and purposes. A bit like how Newtonian physics is a practical workable tool for most everday purposes, despite the fact that it is apparently contradicted by quantum theory. Link to comment Share on other sites More sharing options...
TheDon Posted July 23, 2010 Share Posted July 23, 2010 TheDon's wrong, though. If I'm wrong then so is NASA. Are you going to argue with NASA? Link to comment Share on other sites More sharing options...
TheDon Posted July 23, 2010 Share Posted July 23, 2010 I am reminded of my comment in the cheating/pub quiz thread, where I drew the distinction between "the clever clogs answer", and "the pub quiz answer". The stuff about general relativity is the clever clogs answer, the "both at the same time" bit is the pub quiz answer. It's correct to all intents and purposes. You don't even need general relativity for it to be both different. Air resistance isn't anything special. Think of it like dropping things into a bathtub, the lighter object "floats" down slower than the heavier one. It's EXACTLY the same principle dropping something in air, only airs less dense than water, so the slowing effect isn't as pronounced. Anyone that says dropping two things of different weights in will mean they hit the ground at the same time in anything other than a vacuum is wrong, pure and simple. It's only inside the vacuum they're wrong for extremely clever clogs reasons and the difference will be microscopic. Link to comment Share on other sites More sharing options...
Bazdavies79 Posted July 23, 2010 Share Posted July 23, 2010 So, .............if gravity acts on all objects equally. Then why do I weigh more on the scales than my gf? confused.com Link to comment Share on other sites More sharing options...
CarewsEyebrowDesigner Posted July 23, 2010 Share Posted July 23, 2010 Because you have gots more mass. Link to comment Share on other sites More sharing options...
Bazdavies79 Posted July 23, 2010 Share Posted July 23, 2010 Because you have gots more mass. Have you seen her? only joking hun Link to comment Share on other sites More sharing options...
Bazdavies79 Posted July 23, 2010 Share Posted July 23, 2010 As I have more mass gravity is pulling harder on me? So........objects with differing mass are effected differently by gravity? Would two objects with differing mass hit the ground at the differing times in a vacuum? And surely this contradicts earlier posts stating drag and terminal velocity as being the main factors in air? still confused.com Link to comment Share on other sites More sharing options...
YLN Posted July 23, 2010 Share Posted July 23, 2010 Weight has very little to do with weighing scales Link to comment Share on other sites More sharing options...
LondonLax Posted July 23, 2010 Share Posted July 23, 2010 As I have more mass gravity is pulling harder on me? So........objects with differing mass are effected differently by gravity? Would two objects with differing mass hit the ground at the differing times in a vacuum? And surely this contradicts earlier posts stating drag and terminal velocity as being the main factors in air? still confused.com Your "weight" (the reading on the scales) is your mass multiplied by gravity. The more mass you have the more weight shows up on the scales, gravity acts the same on everything which is why the two objects fall at the same rate in a vacuum. Link to comment Share on other sites More sharing options...
snowychap Posted July 23, 2010 Share Posted July 23, 2010 ...Einstein's theory of relativity that also says the larger object will fall faster, but I can't remember exactly what part of the theory. Wouldn't it say that none of the objects would actually be 'falling'? Anyway, on a less facetious note, would that be to do with tidal effects? Link to comment Share on other sites More sharing options...
blandy Posted July 23, 2010 Moderator Share Posted July 23, 2010 TheDon's wrong, though. If I'm wrong then so is NASA. Are you going to argue with NASA? The bit you're wrong about is your explanation. What you want is one of the most well known equations, f = ma, the force acting downwards on the heavier object is going to be higher than the lighter object due to the higher mass....The drag on both objects is going to be the same at the start....Each object will stop accelerating when the drag is equal to ma, which happens far faster for the lighter object. In a vacuum, you said (rightly) that they will both hit the ground together. In a vacuum drag =0. Taking the F=Ma equation you mention, your explanation implies that as the drag on both objects is the same (zero) and that the force on the object with the greater mass is greater, and that it will not stop accelerating and therefore will, because of the greater force have greater acceleration and therefore greater velocity....hit the ground first, but this is inconsistent with your assertion that they will both hit the ground together (in the vacuum). I just think it's poorly explained. The acceleration for both will be identical at 9.8 m per second per second, the drag will be the same (zero) therefore their rate of change of position will be the same, and that's why they will hit together in the vacuum. In the real world (paddy's desk) the downwards forces will be as per the vacuum scenario, the drag will be the same for each object, as they are the same size and shape, but for the object with more mass there will need to be more force from drag acting against it to stop it accelerating, so it's terminal velocity will be greater, though this will have negligeable affect unless the objects are dropped from a great height, as neither will reach terminal velocity before hitting the desk/floor. Link to comment Share on other sites More sharing options...
TheDon Posted July 23, 2010 Share Posted July 23, 2010 As I have more mass gravity is pulling harder on me? So........objects with differing mass are effected differently by gravity? Would two objects with differing mass hit the ground at the differing times in a vacuum? And surely this contradicts earlier posts stating drag and terminal velocity as being the main factors in air? still confused.com Two objects with differing mass have gravity exerting different forces on them. The net effect of those forces is the same. It's the classic F = ma a = 9.8m/s, that's constant, acceleration due to gravity. F = your weight (weight is a force due to gravity). m = your mass. You weigh more than her because gravity needs to exert a greater force on your mass to accelerate it at a rate of 9.8m/s, however you're not actually measuring your weight, you're measuring your mass. In a vacuum that's the only force in effect (well, mostly, it's not but the other really don't matter that much) so despite two objects having different downward forces acting on them they'll hit the ground at the same time, as nothing is retarded the motion, they're both accelerating at 9.8m/s. Outside of a vacuum you get drag. Two objects of equal size, shape, but different mass have the same drag co-efficient. The same drag co-efficient means they'll generate the same drag whilst moving through air, which will retard the downward motion. Now the heavier object has a higher downward force acting on it than the lighter (as it needs more force to get it accelerating at 9.8m/s. This means that despite the drag on both being equal, it retards the lighter object more, because it counteracts a larger proportion of the gravitational force. The equation to work out an objects terminal velocity is: Vt = sqrt( (2mg)/(pACd) ) where m = mass g = acceleration due to gravity p = density of the fluid the object is moving through (in this case air) A = area of the object Cd = the drag co-efficient. With two objects of equal size and shape then g, p, A and Cd are all equal. m is the only thing that changes in the equation, meaning a higher mass is a higher terminal velocity. Link to comment Share on other sites More sharing options...
PompeyVillan Posted July 23, 2010 Share Posted July 23, 2010 I must commend TheDon on his use of 'retards' in his previous post. I had no idea it could be used in that context. Link to comment Share on other sites More sharing options...
Qwpzxjor1 Posted July 23, 2010 Share Posted July 23, 2010 I did A Level Physics but this thread is making my head hurt. Link to comment Share on other sites More sharing options...
Recommended Posts