Cool example of gravity

[GPIDEAL]

Are you moving right now? Probably you would say no but in fact you are on the surface of the earth that is rotating making you go at something like 400 m/s, revolving around the sun at around 30,000 m/s, our solar system revolving around the galaxy at 222,000 m/s and our galaxy is moving at some other ridiculous speed.

Simply put, movement is relative to how you observe it.

Put in a more simplistic example, if you are sitting still in your car you are also moving at the same speed as your car.

Excellent basketcase.

Would another example be a parachutist falling but being filmed by the other parachutist next to him?

It doesn't seem like you're falling until one of them pulls the ripcord, then they appear to fly up but it's the cameraman who hasn't deployed his chute yet and speeds down past the other guy.

I recently bought a science magazine (Popular Science special edition - can't recall), which feature was about Time (I think the cover simply said TIME or something to that effect - no not the news magazine lol).

They went through one example of time dilation, but it still perplexes the mind.

 

[basketcase]

Imagine that! A camera underwater gets the same sort of pix in zero G, as on Earth! Proves pixels have no mass I guess. And something mebbe about surface tension.

The ISS is not really zero G so the mass argument wouldn't hold. It's just the station is 'falling' towards the earth at the same rate as everything in it so things float in a relative sense. Also objects aren't pushing against each other in the way we experience mass on earth.

On earth g=9.8 m/s^2. On the ISS it is around 8.8. Not really that much of a reduction.

 

[basketcase]

I think Newton would beg to differ.
...
Perspective is relative but we can prove mathematically that the earth didn't move towards the ball.

Actually Newton would disagree with you. He'd just say that because of its mass the movement of the Earth is so insignificant you can't measure it. As far as Newtonian mechanics goes it's a significant distinction.

 

[basketcase]

...
They went through one example of time dilation, but it still perplexes the mind.

The idea of mass under modern physics also blows my mind. Good thing I'm an engineer and only have to deal with the practical aspects of physics.

 

[MRBJX]

Brian Cox, Carl Sagan 2.0?

not a chance

 

[GPIDEAL]

They are travelling along a straight line in spacetime, which is curved by gravity, under pure inertia with no force acting on them. This is a consequence of relativity, where you can take any object in space and use it as the frame of reference for the rest of the universe.

If there's no force acting upon them, how can they be travelling along space-time? OR is it only the inertial force from the earth's spin that is acting upon them to make them 'fall' towards the earth (much like test pilots in a giant centrifuge experience multiple G forces on their bodies)?

 

[GPIDEAL]

[video]http://useloos.com/mediaplayer/?itemid=34212[/video]

God bless Galileo.

 

[jazzpig]

Actually Newton would disagree with you. He'd just say that because of its mass the movement of the Earth is so insignificant you can't measure it. As far as Newtonian mechanics goes it's a significant distinction.

At the risk of sounding stupid here it goes.
If the earth is moving, however insignificant, towards a specific "falling" object, that would mean that a "falling" object on the opposite side of the planet would not
make contact with the earth, seeing that the earth is moving away from it in the direction of the other "falling "object.
Hope it's clear.

 

[RandyAndy2]

If there's no force acting upon them, how can they be travelling along space-time? OR is it only the inertial force from the earth's spin that is acting upon them to make them 'fall' towards the earth (much like test pilots in a giant centrifuge experience multiple G forces on their bodies)?

If I remember my high school physics correctly, a force acting on an object would cause an acceleration according to F=mA. Therefore an object can travel at a constant velocity without a force acting on it (of course a force would be required to get it to that constant velocity).

 

[GPIDEAL]

If I remember my high school physics correctly, a force acting on an object would cause an acceleration according to F=mA. Therefore an object can travel at a constant velocity without a force acting on it (of course a force would be required to get it to that constant velocity).

Right, but subject to a vacuum or no resistance. You get a gold star.

But this doesn't answer my question about why the feather and ball are travelling in the first place, as stated by Fuji.

 

[GPIDEAL]

At the risk of sounding stupid here it goes.
If the earth is moving, however insignificant, towards a specific "falling" object, that would mean that a "falling" object on the opposite side of the planet would not
make contact with the earth, seeing that the earth is moving away from it in the direction of the other "falling "object.
Hope it's clear.

But we know that doesn't happen. That falling object in China (if you will) will be pulled by gravity too.

 

[oldjones]

The ISS is not really zero G so the mass argument wouldn't hold. It's just the station is 'falling' towards the earth at the same rate as everything in it so things float in a relative sense. Also objects aren't pushing against each other in the way we experience mass on earth.

On earth g=9.8 m/s^2. On the ISS it is around 8.8. Not really that much of a reduction.

Science wins; I wasn't arguing anything, just looking at the pix. Which looked much like what you'd see if you put the camera in a sink. Although here on Earth you'd have to hide whatever your 'astronauts' were pushing against to look like they were floating in zero-G, we've all seen (maybe even done) that before.

<Insert remark about the relativity of looking out from a weightless watery universe and seeing nothing unusual, whereas looking from the outside in … >

 

[IM469]

Actually Newton would disagree with you. He'd just say that because of its mass the movement of the Earth is so insignificant you can't measure it. As far as Newtonian mechanics goes it's a significant distinction.

Yes the earth will have the same 'pull' but the comment was 'No one standing on the earth has anyway of proving the Earth......didn't move towards the ball and feathers until they collided.'

The shear size of the earth makes it such that if the ball & feathers was fixed in space such that only the earth could move, it would take billions of years to accellerate enough to reach the ball & feathers. Also picture a plane trying to land on the opposite side of the world as the earth accelerates 32 ft/sec2 away from the plane towards the ball & feathers.

 

[basketcase]

At the risk of sounding stupid here it goes.
If the earth is moving, however insignificant, towards a specific "falling" object, that would mean that a "falling" object on the opposite side of the planet would not
make contact with the earth, seeing that the earth is moving away from it in the direction of the other "falling "object.
Hope it's clear.

Clear but wrong.

If you dropped a really large mass on one side and a small mass on the other side of the earth, each of those masses experience a gravitational force towards the earth and therefore accelerate towards it.

The Earth experiences two forces and will accelerate in the direction of the net force. Since one force is much longer then the Earth will move a fraction of a mm towards the heavy one and away from the light one. The only difference is that he light mass will hit the Earth a fraction of a second later (and because of the huge mass of the Earth those fractions are both so small that they are practically unnoticeable).

Now if you manged to precisely match two identical objects at exact opposite sides of the Earth taking into account all of the irregularities then the forces would cancel out and the Earth wouldn't move (except relative to the objects).

 

[GPIDEAL]

Clear but wrong.

If you dropped a really large mass on one side and a small mass on the other side of the earth, each of those masses experience a gravitational force towards the earth and therefore accelerate towards it.

The Earth experiences two forces and will accelerate in the direction of the net force. Since one force is much longer then the Earth will move a fraction of a mm towards the heavy one and away from the light one. The only difference is that he light mass will hit the Earth a fraction of a second later (and because of the huge mass of the Earth those fractions are both so small that they are practically unnoticeable).

Now if you manged to precisely match two identical objects at exact opposite sides of the Earth taking into account all of the irregularities then the forces would cancel out and the Earth wouldn't move (except relative to the objects).

Why would the Earth move towards these two masses (especially the larger one, albeit a fraction of a mm)? I thought you said that those masses would accelerate towards the earth due to gravity?