Answer is here …
https://www.youtube.com/watch?v=b_8LFhakQAk
Not what I expected.
wait.. why didn’t he submerge the ping pong ball?
it wouldn’t have made any difference arts. as explained it is still part of the system.
comment Let us reason this way: when you hold and submerge the metal ball, you feel that it is getting lighter. That difference goes to the scale.
ChrispenEvan said:
it wouldn’t have made any difference arts. as explained it is still part of the system.
ok.. because it’s fully inside the beaker and not being ‘supported’ by anything other than the system?
yeah
The steel ball pushes against the water.
i’m sure that if you hung the steel ball from a scale it would show it to be lighter when it was submerged than when not.
Well, it turned out just as i expected it would.
As to ‘why’: i won’t even begin to comment, because such things inevitably show that i was right, but my line of reasoning was wildly incorrect.
captain_spalding said:
Well, it turned out just as i expected it would.As to ‘why’: i won’t even begin to comment, because such things inevitably show that i was right, but my line of reasoning was wildly incorrect.
I’m dumber than you guys cause I don’t know
i reckon if it was measured the amount the scale moved would be equal to the difference between the weight of the ball and the weight of the water it displaces.
Having an eye for things uncentred and unlevel, which had me getting the ruler out, and the pivot is 3-4mm further to the right, on my screen.
Doesn’t this explain it?
http://physics.weber.edu/carroll/archimedes/principle.htm
http://physics.weber.edu/carroll/archimedes/principle.htm
eureka!
;-)
Do I have to use my last few cents and do a recharge, or is someone going to tell me? The ping pong ball beaker goes down?
https://www.youtube.com/watch?v=b_8LFhakQAk
——————————————————
No fair. The ping pong ball was a floating…
http://physics.weber.edu/carroll/archimedes/principle.htm
————————————————————
Nup but yes…
The displacement being equal, the pong ball not being crushed, the level will be level.
Thanks for coming.
https://www.youtube.com/watch?v=_rEQAPsNdh4
—————————————————————————
This also is an excellent demonstration of Archimedes law..
Enjoy.
I’ve only looked at Bill’s post.
If they both displace the same amount of water, it shouldn’t make any difference. I may well be wrong. I’m not so good at the fizziks.
Watches video
Bugger me. I really am crap at fizziks
Goes off to read more
OK.
It makes sense now.
Ta for my daily leaning :)
Arts said:
wait.. why didn’t he submerge the ping pong ball?
It was too hard to, once he’d already put the water in. But you respect his authority when he’s says it doesn’t matter don’t you?
Soso said:
Arts said:
wait.. why didn’t he submerge the ping pong ball?
It was too hard to, once he’d already put the water in. But you respect his authority when he’s says it doesn’t matter don’t you?
(shrugs) just glue it to the bottom
But you respect his authority when he’s says it doesn’t matter don’t you?
———————————————————
Of course.
But how much does a suspended ping ball ball weigh?
Mr Ironic said:
But you respect his authority when he’s says it doesn’t matter don’t you?
———————————————————Of course.
But how much does a suspended ping ball ball weigh?
About the same as an orange in the dark.
About the same as an orange in the dark.
———————————————————————
So that confirms it.
The suspended ball has a negative weight.
Ta.
The suspended ball has a negative weight.
wtf is a negative weight?
ChrispenEvan said:
The suspended ball has a negative weight.wtf is a negative weight?
Buoyancy.
ahhhh. so there is a proper word for it.
;-)
ahhhh. so there is a proper word for it.
;-)
———————
You cave so easily.
Arts said:
wait.. why didn’t he submerge the ping pong ball?
He isn’t conducting the same experiment as shown in the diagram in the OP.
I’ve only glanced at the rest of the thread, but it seems that people are defending the result demonstrated in the video.
The video and the diagram are different experiments, because the Ping pong ball is not submerged in the video. Had the Ping pong ball been submerged as an initial condition, the volume of water in the containers would be different to the volumes that the dude in the video started with.
Maybe… Even as I was typing I was losing confidence in this interpretation.
also if the ping pong ball was affixed to the bottom of the container its buoyancy would be exerting an upward force on the container and thus making it lighter.
PermeateFree said:
Doesn’t this explain it?http://physics.weber.edu/carroll/archimedes/principle.htm
No, because the Ping pong ball in the OPs experiment purposefully circumvents the effects of Archimedes Principle by forcefully submerging the Ping pong ball.
ChrispenEvan said:
it wouldn’t have made any difference arts. as explained it is still part of the system.
Based on the diagram in the OP, it makes a difference to the initial amount of water in the pp-ball beaker.
In the situation shown in the diagram, the scales would stay level.
That is a very poorly demonstrated experiment.
He has assumed the answer at the outset.
No marks.
transition said:
Do I have to use my last few cents and do a recharge, or is someone going to tell me? The ping pong ball beaker goes down?
Transition,
In the video they start with two equally full beakers of water on a balance. He floats a ping pong ball in one beaker, and suspends the steel ball in the other.
What he is demonstrating in the video is that the water in the second beaker takes some of the weight of a suspended steel ball (as in, the steel ball has some degree of bouyancy, even if not enough to see it float).
esselte said:
transition said:
Do I have to use my last few cents and do a recharge, or is someone going to tell me? The ping pong ball beaker goes down?
Transition,
In the video they start with two equally full beakers of water on a balance. He floats a ping pong ball in one beaker, and suspends the steel ball in the other.
What he is demonstrating in the video is that the water in the second beaker takes some of the weight of a suspended steel ball (as in, the steel ball has some degree of bouyancy, even if not enough to see it float).
Also meant to say in there somewhere, in the video the balance tips to one side when the steel ball is suspended in it, with the Ping pong ball floating in the other beaker.
What if it’s on a conveyor belt on the horizon at full moon?
esselte said:
esselte said:Transition,
In the video they start with two equally full beakers of water on a balance. He floats a ping pong ball in one beaker, and suspends the steel ball in the other.
What he is demonstrating in the video is that the water in the second beaker takes some of the weight of a suspended steel ball (as in, the steel ball has some degree of bouyancy, even if not enough to see it float).
Also meant to say in there somewhere, in the video the balance tips to one side when the steel ball is suspended in it, with the Ping pong ball floating in the other beaker.
Esselte, what’s the difference between dropping the table-tennis ball in the beaker of water so that it floats on the water and attaching it to the beaker, and holding it underwater, by a piece of string?
OCDC said:
What if it’s on a conveyor belt on the horizon at full moon?
depends if it’s orientated true north or magnetic north…
>Esselte, what’s the difference between dropping the table-tennis ball in the beaker of water so that it floats on the water and attaching it to the beaker, and holding it underwater, by a piece of string?
zero
transition said:
>Esselte, what’s the difference between dropping the table-tennis ball in the beaker of water so that it floats on the water and attaching it to the beaker, and holding it underwater, by a piece of string?zero
COG on that side would be different, but not enough to change the results of the overall test
I think the key question is whether the amount of water in the beakers is the same before the balls are added, or are they levelled out with the balls in there first.
I gather the immersion of the externally suspended steel ball results in the beaker containing it and water going downward?
Wocky said:
Esselte, what’s the difference between dropping the table-tennis ball in the beaker of water so that it floats on the water and attaching it to the beaker, and holding it underwater, by a piece of string?
The volume (and hence, the weight) of water required in the respective beakers to bring the water to the same level.
If the guy in the video had fully submerged his ping pong ball, he would have to remove water from that beaker to make it level with the other beaker,as shown in the OP diagram.
A ping-pong is glued to the bottom of the beaker and water is then added covering the ball until the overflow is reached. This means the water volumne of the ball has been displaced.
The second beaker is filled to the overflow level and when the steel ball is added, its volumne is also displaced via the overflow, thereby making the same amount of water in each beaker.
Question 1. What effect does the boyancy of the ping-pong ball have? Bearing in mind it is attached to the beaker?
Question 2. What effect does a steel ball have on the beaker weight when suspended in the water?
It would seem to me that the forces giving uplift would be greater with the ping-pong ball than with the steel ball, therefore the beaker with the ping-pong ball would be lighter.
If I am incorrect (which is very likely), would you please explain?
I don’t get why people have made this so complicated and ‘tricky’.
OCDC said:
I don’t get why people have made this so complicated and ‘tricky’.
Was the OP right, but for the wrong reason?
PermeateFree said:
OCDC said:
I don’t get why people have made this so complicated and ‘tricky’.
Was the OP right, but for the wrong reason?
The initial experiment when the ping-pong ball was not attached to the beaker and therefore floated, was a typical Archimedes Principle situation, but once attached to the beaker became a buoyancy problem. So what the original experimenter did was mix scientific principles, or simply cocked up the experiment.
PermeateFree said:
PermeateFree said:
OCDC said:
I don’t get why people have made this so complicated and ‘tricky’.
Was the OP right, but for the wrong reason?
The initial experiment when the ping-pong ball was not attached to the beaker and therefore floated, was a typical Archimedes Principle situation, but once attached to the beaker became a buoyancy problem. So what the original experimenter did was mix scientific principles, or simply cocked up the experiment.
The ping-pong ball adds a small mass to the left side. The steel ball adds a larger mass to the right side. The volume of water is the same regardless. The ping-pong ball does not add lift. It is exactly the same as adding the same volume of oil to the left side – the oil will float on the water, and add mass, but less mass than the same volume of steel.
PermeateFree said:
PermeateFree said:
OCDC said:
I don’t get why people have made this so complicated and ‘tricky’.
Was the OP right, but for the wrong reason?
The initial experiment when the ping-pong ball was not attached to the beaker and therefore floated, was a typical Archimedes Principle situation, but once attached to the beaker became a buoyancy problem. So what the original experimenter did was mix scientific principles, or simply cocked up the experiment.
By that brilliant logic, PF, I can lify myself off the ground by pulling on my own bootstraps. Buoyancy has nothing to do with it.
The ping-pong ball does not add lift….
i was hoping someone would comment on my post. i did wait until i thought it was all done and dusted.
:-0
I do however have a “friend” now…
https://www.facebook.com/lydia.nieves2?fref=pb
ChrispenEvan said:
The ping-pong ball does not add lift….i was hoping someone would comment on my post. i did wait until i thought it was all done and dusted.
:-0
i know but it still applies.
:-)
OCDC said:
I don’t get why people have made this so complicated and ‘tricky’.
Physicists – complicating life since 1460
OCDC said:
PermeateFree said:
PermeateFree said:Was the OP right, but for the wrong reason?
The initial experiment when the ping-pong ball was not attached to the beaker and therefore floated, was a typical Archimedes Principle situation, but once attached to the beaker became a buoyancy problem. So what the original experimenter did was mix scientific principles, or simply cocked up the experiment.
No.The ping-pong ball adds a small mass to the left side. The steel ball adds a larger mass to the right side. The volume of water is the same regardless. The ping-pong ball does not add lift. It is exactly the same as adding the same volume of oil to the left side – the oil will float on the water, and add mass, but less mass than the same volume of steel.
Seems like most of us are probably wrong; below is an extract from another forum discussing this exact subject. And on thinking further on the matter the quote below makes a lot of sense.
>>Buoyancy is a complete red herring.The steel ball exerts no force downwards because it is suspended on a string outside the experiment. If I dangle a steel ball in my bathtub full of water it doesn’t make the bathtub full of water heavier.
The string holding the ping pong ball is similarly irrelevant, it just makes it look like there might be something pushing the left side up.<<Last post on: http://www.eurogamer.net/forum/thread/260340
And here is a theory for everyone:
http://www.reddit.com/r/Physics/comments/1mdw6g/a_pretty_interesting_physics_riddle_what_are_your/
Ok, watch carefully, as I am only going to do this once.
Two plastic cups. One has inside it a sealed hollow plastic container, tethered to the bottom with a piece of fishing line. So that side is slightly heavier and tips the scales that way.
I have two tumblers of water and another sealed plastic container with some lead shot in it, and a piece of fishing line to hang it from. The two small containers are identical in volume.
The overall setup
Now with the same amount of water added to each cup. See how the internal tethered container floats. The position of the balance is unchanged.
Now I dip the container with the lead shot into the cup of water on the left. The balance is immediately thrown to that side.
In real life, the effect is quite dramatic and I spilled quite a bit of water setting this up.
morrie said:
Ok, watch carefully, as I am only going to do this once.Two plastic cups. One has inside it a sealed hollow plastic container, tethered to the bottom with a piece of fishing line. So that side is slightly heavier and tips the scales that way.
I have two tumblers of water and another sealed plastic container with some lead shot in it, and a piece of fishing line to hang it from. The two small containers are identical in volume.
The overall setup
Now with the same amount of water added to each cup. See how the internal tethered container floats. The position of the balance is unchanged.
Now I dip the container with the lead shot into the cup of water on the left. The balance is immediately thrown to that side.
In real life, the effect is quite dramatic and I spilled quite a bit of water setting this up.
Very good morrie. Could you explain the principles involved or not involved?
morrie said:
Ok, watch carefully, as I am only going to do this once.
isn’t replication the cornerstone of science? :)
well done, Morrie.. thanks for setting that up
PermeateFree said:
Very good morrie. Could you explain the principles involved or not involved?
I think that the principles have been explained quite well elsewhere in the thread. The tethered internal container is part of the system and makes no difference to anything. That is illustrated by the first two pictures.
The container with the lead shot is supported externally. It displaces water. That creates a buoyancy force, supplied by the left hand side of the balance. The actual mass of the container with the lead shot is irrelevant. It is only the volume that matters.
morrie said:
PermeateFree said:Very good morrie. Could you explain the principles involved or not involved?
Thanks. I would like to have done it as a video, but it takes a lot more effort, particularly working on your own.I think that the principles have been explained quite well elsewhere in the thread. The tethered internal container is part of the system and makes no difference to anything. That is illustrated by the first two pictures.
The container with the lead shot is supported externally. It displaces water. That creates a buoyancy force, supplied by the left hand side of the balance. The actual mass of the container with the lead shot is irrelevant. It is only the volume that matters.
Great, many thanks. Not as simple as first appears.
balanced well enough, does it work with air instead of water?
The pressure in the beaker varies over the vertical span with height of the fluid in the beaker, more at the bottom, less toward the top, which puts more pressure on the bottom surface of the externally suspended weight.
The pressure gradient is being used.
http://en.wikipedia.org/wiki/Pressure_gradient_force
transition said:
The pressure in the beaker varies over the vertical span with height of the fluid in the beaker, more at the bottom, less toward the top, which puts more pressure on the bottom surface of the externally suspended weight.
Carmen_Sandiego said:
morrie said:
Carmen_Sandiego said:
So much for maths and physics.
What is your take on the maths morrie?
PermeateFree said:
morrie said:
Carmen_Sandiego said:
So much for maths and physics.What is your take on the maths morrie?
morrie said:
PermeateFree said:
morrie said:So much for maths and physics.
What is your take on the maths morrie?
It is wrong, somewhere. I can’t be bothered working through it.
Stuffed up a lot of people apparently. Anyway time I was in bed.
Nite.
Take away the pivot scales, have regular scales, make it one beaker, lower the ball to different levels in the water and measure.
Pivot scales are dodgy anyway, the geometry changes as they pivot, and worse if the pivot isn’t kept shallow and anything with any height being measured.
The steel ball or whatever used doesn’t have zero buoyancy, it’s just that it is more dense than water, but note if you drop a steel cannon ball into the sea it will get to certain speed and as it gets into deeper water then slows.
From the perspective of hydraulics an externally fixed object in a water-filled beaker changes the pressure gradient profile of the water being attracted downward by gravity. The pressure gradient profile then works forces between the steel ball or whatever and the floor of the beaker. Keeping in mind that atmospheric pressure exists because of gravity.
Atmospheric pressure has it’s own pressure gradient.
In a sense, like a externally fixed loose fitting piston, some of the force and weight of the water above the immersed object weigh on the immersed object, by way of pressure being a fluid, but the pressure gradient increase underneath (conveyed by it being a liquid, still a mechanism) results in a force between the immersed object and the beaker bottom.
Esentially the ‘coupling’ via the pressure gradient changes not the total weight of the water, but the density distribution over, above and around the steel ball or whatever immersed.
The steel ball is in fact no different to the ping pong ball being immersed, the effect is the same, meaning the externally fixed steel or lead shot or whatever could be replaced with a ping pong ball.
The pressure gradient is a or even ‘the’ coupling mechanism. The different density balls/immersed objects and pivot scales are just a bullshit distraction.
It throws people because the coupling mechanism forces aren’t entirely material coupling mechanisms.
Pivot scales are dodgy anyway, the geometry changes as they pivot, and worse if the pivot isn’t kept shallow and anything with any height being measured.
please show working. precision balances have been used for centuries. they have limitations in precision maybe and are thus not used much any more. but for an experiment like this they are hardly needed anyway. so show why these scales are dodgy.
can you try it with the oil instead of pingpong ball?
>please show working. precision balances have been used for centuries. they have limitations in precision maybe and are thus not used much any more. but for an experiment like this they are hardly needed anyway. so show why these scales are dodgy.
Because whatever sitting on them (take Morrie’s homemade example) would have to be kept perfectly vertical (or parallel) and centre as they tilt.
Anyway the point of the post was to do with pressure gradients and coupling this way.
>Take away the pivot scales, have regular scales, make it one beaker, lower the ball to different levels in the water and measure.
I don’t have to do that experiment as I know the answer. The depth makes no difference. Neither does the shape of the object, once it is immersed. This is a standard method of measuring volume.
morrie said:
>Take away the pivot scales, have regular scales, make it one beaker, lower the ball to different levels in the water and measure.I don’t have to do that experiment as I know the answer. The depth makes no difference. Neither does the shape of the object, once it is immersed. This is a standard method of measuring volume.
>I don’t have to do that experiment as I know the answer. The depth makes no difference. Neither does the shape of the object, once it is immersed. This is a standard method of measuring volume.
More was about how the viewer may see the unnecessarily convoluted experiment, morrie.
transition said:
>I don’t have to do that experiment as I know the answer. The depth makes no difference. Neither does the shape of the object, once it is immersed. This is a standard method of measuring volume.More was about how the viewer may see the unnecessarily convoluted experiment, morrie.
>If you like to look at it from your point of view, the integral of the pressure across the surface is the same at all depths and for all objects of equal volume.
Yeah different displacement volume shapes went through my head, so what’s the story with a very slim vertical whatever compared with a very thin wide whatever, the displacement is the same, so I suppose the overall pressure gradient force is the same, or not? I guess for real possible examples excepting the academic ones that approach infinity it is, though intuitively the physics in my head says a tall suspended weight has a greater pressure gradient. In fact it tends me to think an inverted conical shape has a greater one, but I think not.
transition said:
>I don’t have to do that experiment as I know the answer. The depth makes no difference. Neither does the shape of the object, once it is immersed. This is a standard method of measuring volume.More was about how the viewer may see the unnecessarily convoluted experiment, morrie.
I’m afraid the added simplicity of the alternative explanation escaped me.
>I’m afraid the added simplicity of the alternative explanation escaped me.
:) lucky you added an equal measure of humour in each beaker.
transition said:
>I’m afraid the added simplicity of the alternative explanation escaped me.:) lucky you added an equal measure of humour in each beaker.
Usually helps :)
>can you try it with the oil instead of pingpong ball?
Just wondering if you used oil, or something perhapss not given to evaporate, say single beaker on scales, made the setup a solidly mounted ball immersed from above, and put it in a chamber and vacuated the chamber, what then?
You still have gravity acting on the liquid mass, but no atmospheric pressure. You still have a pressure gradient courtesy of gravity.
The experiment is a variant of the question of why farts in the bath rise to the surface, even when the bath you’re sitting in is accelerating into a black hole, perhaps no matter what the orientation of the bath?
I’m afraid the added simplicity of the alternative explanation escaped me.
————————————————————-
Beside the point that you cannot add simplicity.
The immersed cups are inverted…
Well one of them is…
the only thing I can see here is this
if both balls are the same volume then it means the beakers both have the same amount of water in them
the metal ball being held by the string doesn’t transfer any weight to the water in the beaker
when you put the metal ball in the beaker with it being suspended by the string I think it just displaces the water rather than push the scale down, if the metal ball suddenly expanded then it would just push the water up past the ball rather than push the scale down
so the scale stays the same?