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Why doesn't a table tennis ball float on a surface of steel balls? How do we calculate buoyancy here?
The Next CEO of Stack OverflowWhy do the big nuts always remain at top? The Brazil-nut EffectPing-pong ball pontoonWhy does rubber ball bounce back while iron ball doesn't?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?What are the physics behind a table tennis ball launcher?Question about buoyancy force affecting mass measurementHow high should be the edge of a billiard table to not allow undesirable pressures on balls when bouncing off?Physics of a table tennis launcherWhy did this table tennis ball rise to the sky?
$begingroup$
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?
newtonian-mechanics forces classical-mechanics fluid-dynamics
edited Mar 29 at 8:56
curiousdannii
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
$endgroup$
add a comment |
$begingroup$
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?
newtonian-mechanics forces classical-mechanics fluid-dynamics
edited Mar 29 at 8:56
curiousdannii
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
$endgroup$
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
add a comment |
$begingroup$
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?
newtonian-mechanics forces classical-mechanics fluid-dynamics
edited Mar 29 at 8:56
curiousdannii
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
$endgroup$
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?
newtonian-mechanics forces classical-mechanics fluid-dynamics
newtonian-mechanics forces classical-mechanics fluid-dynamics
edited Mar 29 at 8:56
curiousdannii
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
edited Mar 29 at 8:56
curiousdannii
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
edited Mar 29 at 8:56
curiousdannii
612614
edited Mar 29 at 8:56
curiousdannii
612614
edited Mar 29 at 8:56
curiousdannii
612614
612614
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
asked Mar 28 at 7:02
enbin zhengenbin zheng
9417
9417
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
add a comment |
10
$begingroup$
Shake the bowl a little. Like Brownian motion on water molecules.
$endgroup$
– Hot Licks
Mar 28 at 19:31
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
add a comment |
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
279k44557804
$endgroup$
7
$begingroup$
-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
12
$begingroup$
@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
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
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
279k44557804
$endgroup$
7
$begingroup$
-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
12
$begingroup$
@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
279k44557804
$endgroup$
7
$begingroup$
-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
12
$begingroup$
@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
279k44557804
$endgroup$
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
279k44557804
edited Mar 28 at 8:03
answered Mar 28 at 7:55
John RennieJohn Rennie
279k44557804
answered Mar 28 at 7:55
John RennieJohn Rennie
279k44557804
answered Mar 28 at 7:55
John RennieJohn Rennie
279k44557804
279k44557804
7
$begingroup$
-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
12
$begingroup$
@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
7
$begingroup$
-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
12
$begingroup$
@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
7
7
$begingroup$
-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
12
12
$begingroup$
@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
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
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
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
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
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
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
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Mar 28 at 7:59
answered Mar 28 at 7:49
David NewellDavid Newell
312
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered Mar 28 at 7:49
David NewellDavid Newell
312
answered Mar 28 at 7:49
David NewellDavid Newell
312
312
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
David Newell is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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Check out our Code of Conduct.
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Can't the steel balls float a table tennis ball even if they are very small?
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– 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.
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– Hot Licks
Mar 28 at 19:31