TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 So I have have a gravitational pull because I have mass? In space I would attract objects(hypothetically) due to my mass, ... Yes, basically, in both the Newtonian (classical) and Einsteinian (relativistic) theories of gravity, you gravitationally attract objects because you have mass. What the mass is supposedly doing is different for both views (Einsteins being more modern and a better description of nature, but Newtons being simpler and therefore still used in many cases). In the classical view, your mass 'reaches out', instantaneously across any distance in space, and pulls on other masses. In general relativity, your mass warps the spacetime (primarily) in your vicinity, giving matter moving in that area its 'local marching orders' - how it is to move. Simply put, mass warps spacetime and warped spacetime affects the motion of matter. Both views have the strength of gravity falling off according the inverse square law: that is, double the distance and the strength drops to one fourth what it was. However, Einstein says that gravity isn't really a force since it can be transformed away. Consider an spacestation: by being placed into a state of free fall, the occupants feel no gravity (or 'microgravity') even though they are immersed in a strong 'gravitational field' - which is what keeps them orbiting the Earth instead of flying off in a straight line into deep space. Smokinjoe9: ... or must I be spinning and have mass? Spinning is not required. Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 Newton's Laws of Inertia state that force is required to change the motion of matter. The force require to accelerate an object is proportionate to the mass of the object. So, the object being forced is not pushing back? It just takes enough force to overcome the mass/weight of object 2.. The second object is pushing back, according to Newton's third law. Consider a billiard ball at rest on a pool table and being hit by a second billiard ball, dead on (no 'English' or spin, not a glancing blow, etc.). The acceleration produced for the formerly at-rest ball will be equal to the force applied to it divided by its mass. You've got all of that. But what about the second ball that struck the formerly at-rest one? If the first ball didn't 'push back' on the second during the collision, then the second ball's motion would not be changed after the collision: yet it clearly is. In fact, if done just right, the formerly at-rest ball will move away with (essentially) the same speed and direction as the originally moving ball, and the original moving ball will end up at rest (essentially) right where the formerly at-rest ball started. The two will have swapped states of motion. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 Yes, basically, in both the Newtonian (classical) and Einsteinian (relativistic) theories of gravity, you gravitationally attract objects because you have mass. So then 2 rocks placed side by side in space would come together? yes/no? However, Einstein says that gravity isn't really a force since it can be transformed away. Consider an spacestation: by being placed into a state of free fall, the occupants feel no gravity (or 'microgravity') even though they are immersed in a strong 'gravitational field' - which is what keeps them orbiting the Earth instead of flying off in a straight line into deep space. The spacestation is orbiting our planet in our gravitational field not the occupants they are in the spacestation. If they were being pulled by the earth's gravity wouldn't they be stuck to the side of the spacestation? humor me please.... Spinning is not required.I'll get to the spinning later, another stumper for me.... Quote Link to comment Share on other sites More sharing options...
Queso Posted May 21, 2005 Report Share Posted May 21, 2005 So then 2 rocks placed side by side in space would come together? yes/no? yes. The spacestation is orbiting our planet in our gravitational field not the occupants they are in the spacestation. If they were being pulled by the earth's gravity wouldn't they be stuck to the side of the spacestation? humor me please.... i'm not exactly sure, but i think it has something to do with the pressure inside. just like when you're in an airplane flying sideways, making a turn...yet the gravity still makes it seem like you are sitting up, when in reality you are sideways to earths gravity. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 The second object is pushing back, according to Newton's third law. Consider a billiard ball at rest on a pool table and being hit by a second billiard ball, dead on (no 'English' or spin, not a glancing blow, etc.). The acceleration produced for the formerly at-rest ball will be equal to the force applied to it divided by its mass. You've got all of that.Got it. The ball moves because of force.. But what about the second ball that struck the formerly at-rest one? If the first ball didn't 'push back' on the second during the collision, then the second ball's motion would not be changed after the collision: yet it clearly is. In fact, if done just right, the formerly at-rest ball will move away with (essentially) the same speed and direction as the originally moving ball, and the original moving ball will end up at rest (essentially) right where the formerly at-rest ball started. The two will have swapped states of motion.Don't got it..and here is why..The energy from the moving ball is transfered when the at rest ball is hit. There was no force greater than the mass/weight of the at rest ball exerted by it...Not so with the moving ball... Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 Pendulum If you swing a weight on a string, it will go back and forth in regular periodic motion. Once it got started, such a pendulum would move back-and-forth forever if it was not for internal friction in the string and air resistance. and gravity? or is that a given? The pendulum is doing work against gravity when the bob swings upward: that is, it's kinetic energy is being converted into gravitational potential energy. But energy is not being lost from the system because of that. The situation in regards to gravity is symmetrical in that the bob gains the same amount of energy in the downswing as it lost in the upswing - the magnitudes of kinetic-to-potential and potential-to-kinetic are the same, in regards to gravity's affects. So gravity itself does not cause the pendulum to come to a stop. What happens is that energy is lost from the system due to non-conservative forces, such as friction (air resistance being a special type of friction). This reduces how high the bob can swing, and since friction occurs - in both directions - during each swing, the bob climbs less high for each swing. Eventually it doesn't have enough energy to climb up at all, and so ends up at the lowest free energy state of the system, which is at the dead center bottom of its swing. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 So then 2 rocks placed side by side in space would come together? Your answer, Yes... Then do to earth's gravity when 2 objects are placed side by side on earth they don't come together? Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 Smokinjoe9: 2 rocks places side by side in space do not attract they just sit there, correct? I mean if I set them side by side(sitting still) in space they will not come together, right? They would come together (assuming the net effect of all other forces acting on them - like the graviational attraction of another mass, like the moon or our sun - is of smaller magnitude that their graviational attraction). Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 Your answer, Yes... Then do to earth's gravity when 2 objects are placed side by side on earth they don't come together? Compare the mass of the entire Earth with one of your little rocks: HUGE difference. And the force of gravitational attraction is proportional to the product of the two objects' masses. So the pull that the Earth exerts a rock is enormously larger than the pull the one of the rocks exerts on each other: their attraction for each other is completely swamped out by the Earth's influence. But note that scientists can show that 2 objects side by side hear at the surface do attract each other gravitationally. I believe it was Cavendish who did this first: they took solid metal spheres and supsended them from wires: they could measure the change in the angle of the devices caused by the "sideways" gravitational attraction between the two lead spheres. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 The pendulum is doing work against gravity when the bob swings upward: that is, it's kinetic energy is being converted into gravitational potential energy. But energy is not being lost from the system because of that. The situation in regards to gravity is symmetrical in that the bob gains the same amount of energy in the downswing as it lost in the upswing - the magnitudes of kinetic-to-potential and potential-to-kinetic are the same, in regards to gravity's affects. So gravity itself does not cause the pendulum to come to a stop. What happens is that energy is lost from the system due to non-conservative forces, such as friction (air resistance being a special type of friction). This reduces how high the bob can swing, and since friction occurs - in both directions - during each swing, the bob climbs less high for each swing. Eventually it doesn't have enough energy to climb up at all, and so ends up at the lowest free energy state of the system, which is at the dead center bottom of its swing. I understand air resistance(hand out the car window), Ok, energy in the downswing caused by gravity, yes/no.....Energy in the upswing against gravity, right? I am working on these theories(that's why the questions), even if you don't believe me..This helps... Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 TeleMad: However, Einstein says that gravity isn't really a force since it can be transformed away. Consider an spacestation: by being placed into a state of free fall, the occupants feel no gravity (or 'microgravity') even though they are immersed in a strong 'gravitational field' - which is what keeps them orbiting the Earth instead of flying off in a straight line into deep space. Smokinjoe9: The spacestation is orbiting our planet in our gravitational field not the occupants they are in the spacestation. If they were being pulled by the earth's gravity wouldn't they be stuck to the side of the spacestation? If the occupants were being pulled by a DIFFERENT STRENGTH of the Earth' gravity then they would. But the spacestation and everything in it experiences the same downward graviational pull, because they are all the same distance from the Earth's center of mass, so they are all effected to the same degree. They all fall towards the Earth is the same arc, so the occupants don't get pushed to one side or the other. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 But note that scientists can show that 2 objects side by side hear at the surface do attract each other gravitationally. I believe it was Cavendish who did this first: they took solid metal spheres and supsended them from wires: they could measure the change in the angle of the devices caused by the "sideways" gravitational attraction between the two lead spheres. Interesting...there could be many reasons for the angle, just a couple, relaxation in the wire, tempurature,I am not doubting the test, I will have to see the results, I am just thinking....Sounds like a good test to make... Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 Don't got it..and here is why..The energy from the moving ball is transfered when the at rest ball is hit. There was no force greater than the mass/weight of the at rest ball exerted by it...Not so with the moving ball... Sorry, I don't understand what you are getting at in this part: "There was no force greater than the mass/weight of the at rest ball exerted by it..." The at-rest ball is hit by the moving ball. The moving ball transfers some (or all) of its kinetic energy to the other ball, causing the other ball to move with a particular accleration, according to Newton's second law. Because the formerly at-rest ball 'pushes back' against the moving ball, in accordance with Newton's third law, the moving ball's velocity changes noticeably. Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 If the occupants were being pulled by a DIFFERENT STRENGTH of the Earth' gravity then they would. But the spacestation and everything in it experiences the same downward graviational pull, because they are all the same distance from the Earth's center of mass, so they are all effected to the same degree. They all fall towards the Earth is the same arc, so the occupants don't get pushed to one side or the other. Got it, more studying.... Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 Sorry, I don't understand what you are getting at in this part: "There was no force greater than the mass/weight of the at rest ball exerted by it..." The at-rest ball is hit by the moving ball. The moving ball transfers some (or all) of its kinetic energy to the other ball, causing the other ball to move with a particular accleration, according to Newton's second law. Because the formerly at-rest ball 'pushes back' against the moving ball, in accordance with Newton's third law, the moving ball's velocity changes noticeably.The ball at rest cannot create force, it can however have mass/weight, therefore the ball at rest cannot "push back"...The moving ball's velocity changes due to contact with another mass/ball, not by the force of the other ball??? I understand once the moving ball comes in contact with the at rest ball, then the at rest ball will cause resistance and accelerate because of mass. how does it push back, it has no force and only resists force? Quote Link to comment Share on other sites More sharing options...
TeleMad Posted May 21, 2005 Report Share Posted May 21, 2005 TeleMad: But note that scientists can show that 2 objects side by side hear at the surface do attract each other gravitationally. I believe it was Cavendish who did this first: they took solid metal spheres and supsended them from wires: they could measure the change in the angle of the devices caused by the "sideways" gravitational attraction between the two lead spheres. Smokingjoe9: Interesting...there could be many reasons for the angle, just a couple, relaxation in the wire, tempurature,I am not doubting the test, I will have to see the results, I am just thinking....Sounds like a good test to make... The results were as predicted by Newton's equation F = G(mM) / d^2 and were attractive. The only force known that would cause this type of relationship - for macroscopic, non-charged objects - is gravity. "The experiment was carefully repeated with different masses at various separations. In addition to providing a value for G, the results showed that the force is attractive, proportional to the produce mM [that is, my M1 * m2], and inversely proportional to the square of the distance r." (College Physics: Fifth Edition, Serway & Faughn, Harcourt College Publishers, 1999, p195-196) Quote Link to comment Share on other sites More sharing options...
Smokinjoe9 Posted May 21, 2005 Author Report Share Posted May 21, 2005 The results were as predicted by Newton's equation F = G(mM) / d^2 and were attractive. The only force known that would cause this type of relationship - for macroscopic, non-charged objects - is gravity. Got it, but sadly if gravity is the cause we need to know what gravity is????I like it, I am still not throughly convinced, the math seems right, but is based on some theoretical data(gravity etc..) i am starting to hate science :note: Quote Link to comment Share on other sites More sharing options...
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