Why doesn't a table tennis ball float on a surface of steel balls? How do we calculate buoyancy here?Why do the big nuts always remain at top? The Brazil-nut EffectPing-pong ball pontoonBackspin in outer space i.e. in a liquid with no viscosity: not changing direction?Terminal velocity of a steel ball in waterPhysics:Buoyant force and scale readingsIn table tennis, is it possible to play a ball in such a way that it does not bounce off the opponents half of the table?Question about buoyancy force affecting mass measurementDoes an object need fluid under it to float?How high should be the edge of a billiard table to not allow undesirable pressures on balls when bouncing off?Pushing Two Balls Into One AnotherWhy do steel Newton's balls work?
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Why doesn't a table tennis ball float on a surface of steel balls? How do we calculate buoyancy here?
Why do the big nuts always remain at top? The Brazil-nut EffectPing-pong ball pontoonBackspin in outer space i.e. in a liquid with no viscosity: not changing direction?Terminal velocity of a steel ball in waterPhysics:Buoyant force and scale readingsIn table tennis, is it possible to play a ball in such a way that it does not bounce off the opponents half of the table?Question about buoyancy force affecting mass measurementDoes an object need fluid under it to float?How high should be the edge of a billiard table to not allow undesirable pressures on balls when bouncing off?Pushing Two Balls Into One AnotherWhy do steel Newton's balls work?
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;
$begingroup$
Place the beaker full of steel balls and submerge the table tennis ball under the steel balls. The table tennis ball does not float up. Why does it not float up? Do table tennis balls float when the diameter of steel balls is reduced? How to calculate the buoyancy of steel balls?
Would it come up without friction?
newtonian-mechanics forces classical-mechanics fluid-dynamics
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
$endgroup$
|
show 2 more comments
$begingroup$
Place the beaker full of steel balls and submerge the table tennis ball under the steel balls. The table tennis ball does not float up. Why does it not float up? Do table tennis balls float when the diameter of steel balls is reduced? How to calculate the buoyancy of steel balls?
Would it come up without friction?
newtonian-mechanics forces classical-mechanics fluid-dynamics
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
$endgroup$
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53
|
show 2 more comments
$begingroup$
Place the beaker full of steel balls and submerge the table tennis ball under the steel balls. The table tennis ball does not float up. Why does it not float up? Do table tennis balls float when the diameter of steel balls is reduced? How to calculate the buoyancy of steel balls?
Would it come up without friction?
newtonian-mechanics forces classical-mechanics fluid-dynamics
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
$endgroup$
Place the beaker full of steel balls and submerge the table tennis ball under the steel balls. The table tennis ball does not float up. Why does it not float up? Do table tennis balls float when the diameter of steel balls is reduced? How to calculate the buoyancy of steel balls?
Would it come up without friction?
newtonian-mechanics forces classical-mechanics fluid-dynamics
newtonian-mechanics forces classical-mechanics fluid-dynamics
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
edited Apr 1 at 22:51
enbin zheng
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
asked Mar 28 at 7:02
enbin zhengenbin zheng
4615 silver badges11 bronze badges
4615 silver badges11 bronze badges
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53
|
show 2 more comments
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53
10
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53
|
show 2 more comments
2 Answers
2
active
oldest
votes
$begingroup$
The ball bearings are behaving as a solid because the forces between the steel balls (i.e. friction) are large enough to hold the balls in position relative to each other.
If you apply enough force to a solid you will cause it to fracture or to cause plastic flow. So for example if you attached a string to the ball and pulled upwards with enough force it would cause the steel balls to flow over each other and the table tennis ball would move up. The force required is related to the yield stress of the solid formed by the steel balls.
You can make the steel balls behave as a fluid by making a gas flow through them. This creates a fluidised bed. The gas pushes the steel balls apart so the friction between them is removed, and in this state the steel balls will behave like a fluid and the table tennis ball would float upwards.
Alternatively just shake the beaker. This is equivalent to adding thermal energy i.e. heating the system until it melts. If you shake the beaker you'll find the table tennis ball floats upwards.
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
$endgroup$
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
|
show 7 more comments
$begingroup$
Well, what if the steel balls were extremely small, say molecular size. In that case, the constraining annulus would look like a polished steel collar, and would likely hold down the ball even if the glass was shattered, underwater, in a swimming pool. . (The van der Waals forces, and metallic bonds, would account for that.)
But this example given, shows discreet balls of intermediate size, and unless they are magnetized, their coupling with the container is what allows restraint of the tennis ball.
If THIS setup was in the bottom of a deeper pool, and the beaker was shattered,
the steel balls would run radially away, and the tennis ball would pop up.
(Note: I answered this as if there was water in the beaker along with the steel balls and tennis ball. But the answer is not changed by my error.)
The term "van der Waals force" is sometimes used loosely for all intermolecular forces.
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
$endgroup$
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
add a comment
|
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The ball bearings are behaving as a solid because the forces between the steel balls (i.e. friction) are large enough to hold the balls in position relative to each other.
If you apply enough force to a solid you will cause it to fracture or to cause plastic flow. So for example if you attached a string to the ball and pulled upwards with enough force it would cause the steel balls to flow over each other and the table tennis ball would move up. The force required is related to the yield stress of the solid formed by the steel balls.
You can make the steel balls behave as a fluid by making a gas flow through them. This creates a fluidised bed. The gas pushes the steel balls apart so the friction between them is removed, and in this state the steel balls will behave like a fluid and the table tennis ball would float upwards.
Alternatively just shake the beaker. This is equivalent to adding thermal energy i.e. heating the system until it melts. If you shake the beaker you'll find the table tennis ball floats upwards.
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
$endgroup$
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
|
show 7 more comments
$begingroup$
The ball bearings are behaving as a solid because the forces between the steel balls (i.e. friction) are large enough to hold the balls in position relative to each other.
If you apply enough force to a solid you will cause it to fracture or to cause plastic flow. So for example if you attached a string to the ball and pulled upwards with enough force it would cause the steel balls to flow over each other and the table tennis ball would move up. The force required is related to the yield stress of the solid formed by the steel balls.
You can make the steel balls behave as a fluid by making a gas flow through them. This creates a fluidised bed. The gas pushes the steel balls apart so the friction between them is removed, and in this state the steel balls will behave like a fluid and the table tennis ball would float upwards.
Alternatively just shake the beaker. This is equivalent to adding thermal energy i.e. heating the system until it melts. If you shake the beaker you'll find the table tennis ball floats upwards.
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
$endgroup$
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
|
show 7 more comments
$begingroup$
The ball bearings are behaving as a solid because the forces between the steel balls (i.e. friction) are large enough to hold the balls in position relative to each other.
If you apply enough force to a solid you will cause it to fracture or to cause plastic flow. So for example if you attached a string to the ball and pulled upwards with enough force it would cause the steel balls to flow over each other and the table tennis ball would move up. The force required is related to the yield stress of the solid formed by the steel balls.
You can make the steel balls behave as a fluid by making a gas flow through them. This creates a fluidised bed. The gas pushes the steel balls apart so the friction between them is removed, and in this state the steel balls will behave like a fluid and the table tennis ball would float upwards.
Alternatively just shake the beaker. This is equivalent to adding thermal energy i.e. heating the system until it melts. If you shake the beaker you'll find the table tennis ball floats upwards.
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
$endgroup$
The ball bearings are behaving as a solid because the forces between the steel balls (i.e. friction) are large enough to hold the balls in position relative to each other.
If you apply enough force to a solid you will cause it to fracture or to cause plastic flow. So for example if you attached a string to the ball and pulled upwards with enough force it would cause the steel balls to flow over each other and the table tennis ball would move up. The force required is related to the yield stress of the solid formed by the steel balls.
You can make the steel balls behave as a fluid by making a gas flow through them. This creates a fluidised bed. The gas pushes the steel balls apart so the friction between them is removed, and in this state the steel balls will behave like a fluid and the table tennis ball would float upwards.
Alternatively just shake the beaker. This is equivalent to adding thermal energy i.e. heating the system until it melts. If you shake the beaker you'll find the table tennis ball floats upwards.
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
edited Mar 28 at 8:03
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
answered Mar 28 at 7:55
John RennieJohn Rennie
287k46 gold badges588 silver badges834 bronze badges
287k46 gold badges588 silver badges834 bronze badges
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
|
show 7 more comments
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
8
8
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
$begingroup$
-1 Shaking the beaker will make the ball float upwards because of the size difference, not the density difference. It's a very different effect. (If you were to reverse the materials of the balls - it is the large steel ball that would end up on top)
$endgroup$
– UKMonkey
Mar 28 at 9:48
4
4
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
$begingroup$
*edit density and size (in effect density including air gaps) here's the wiki article en.wikipedia.org/wiki/Granular_convection
$endgroup$
– UKMonkey
Mar 28 at 9:53
13
13
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
$begingroup$
@UKMonkey it's both size and density. As it happens I explained the effect of size in Why do the big nuts always remain at top? The Brazil-nut Effect.
$endgroup$
– John Rennie
Mar 28 at 10:20
3
3
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
$begingroup$
The linked answer is good but it doesn't explain how buoyancy is different. I've actually never seen a good explanation of the mechanisms underlying buoyancy. Often it's described as if it were a fundamental force.
$endgroup$
– JimmyJames
Mar 28 at 18:11
2
2
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
$begingroup$
Another comparison that would be interesting is how this is or is not related to how a dust particle can hover in still air for a period that is longer than would be expected given relative density to air.
$endgroup$
– JimmyJames
Mar 28 at 18:17
|
show 7 more comments
$begingroup$
Well, what if the steel balls were extremely small, say molecular size. In that case, the constraining annulus would look like a polished steel collar, and would likely hold down the ball even if the glass was shattered, underwater, in a swimming pool. . (The van der Waals forces, and metallic bonds, would account for that.)
But this example given, shows discreet balls of intermediate size, and unless they are magnetized, their coupling with the container is what allows restraint of the tennis ball.
If THIS setup was in the bottom of a deeper pool, and the beaker was shattered,
the steel balls would run radially away, and the tennis ball would pop up.
(Note: I answered this as if there was water in the beaker along with the steel balls and tennis ball. But the answer is not changed by my error.)
The term "van der Waals force" is sometimes used loosely for all intermolecular forces.
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
$endgroup$
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
add a comment
|
$begingroup$
Well, what if the steel balls were extremely small, say molecular size. In that case, the constraining annulus would look like a polished steel collar, and would likely hold down the ball even if the glass was shattered, underwater, in a swimming pool. . (The van der Waals forces, and metallic bonds, would account for that.)
But this example given, shows discreet balls of intermediate size, and unless they are magnetized, their coupling with the container is what allows restraint of the tennis ball.
If THIS setup was in the bottom of a deeper pool, and the beaker was shattered,
the steel balls would run radially away, and the tennis ball would pop up.
(Note: I answered this as if there was water in the beaker along with the steel balls and tennis ball. But the answer is not changed by my error.)
The term "van der Waals force" is sometimes used loosely for all intermolecular forces.
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
$endgroup$
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
add a comment
|
$begingroup$
Well, what if the steel balls were extremely small, say molecular size. In that case, the constraining annulus would look like a polished steel collar, and would likely hold down the ball even if the glass was shattered, underwater, in a swimming pool. . (The van der Waals forces, and metallic bonds, would account for that.)
But this example given, shows discreet balls of intermediate size, and unless they are magnetized, their coupling with the container is what allows restraint of the tennis ball.
If THIS setup was in the bottom of a deeper pool, and the beaker was shattered,
the steel balls would run radially away, and the tennis ball would pop up.
(Note: I answered this as if there was water in the beaker along with the steel balls and tennis ball. But the answer is not changed by my error.)
The term "van der Waals force" is sometimes used loosely for all intermolecular forces.
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
$endgroup$
Well, what if the steel balls were extremely small, say molecular size. In that case, the constraining annulus would look like a polished steel collar, and would likely hold down the ball even if the glass was shattered, underwater, in a swimming pool. . (The van der Waals forces, and metallic bonds, would account for that.)
But this example given, shows discreet balls of intermediate size, and unless they are magnetized, their coupling with the container is what allows restraint of the tennis ball.
If THIS setup was in the bottom of a deeper pool, and the beaker was shattered,
the steel balls would run radially away, and the tennis ball would pop up.
(Note: I answered this as if there was water in the beaker along with the steel balls and tennis ball. But the answer is not changed by my error.)
The term "van der Waals force" is sometimes used loosely for all intermolecular forces.
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
edited Mar 28 at 7:59
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
answered Mar 28 at 7:49
David NewellDavid Newell
312 bronze badges
312 bronze badges
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
add a comment
|
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
$begingroup$
Can't the steel balls float a table tennis ball even if they are very small?
$endgroup$
– enbin zheng
Mar 28 at 18:32
add a comment
|
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10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
$begingroup$
@HotLicks Would it come up without friction?
$endgroup$
– enbin zheng
Apr 1 at 22:58
$begingroup$
Some of the ball bearings sit above the midline of the ping-pong ball and push down on it. Even if the ball bearings too were free of all friction they would still be locked in place by the weight other ball bearings above them.
$endgroup$
– Hot Licks
Apr 2 at 1:56
$begingroup$
@HotLicks Because there is no friction, will the bearing balls at the bottom of the table tennis ball not produce buoyancy to the table tennis ball?
$endgroup$
– enbin zheng
Apr 2 at 2:47
$begingroup$
They will produce buoyancy, but it's not a given that this will be sufficient to overcome the force of the balls pressing down from above, especially since the balls are apt to be "locked" in place due to being wedged together.
$endgroup$
– Hot Licks
Apr 2 at 2:53