What is the largest and smallest floating metal flashlight?

[saabluster]

I found I could get the DEFT to float a while back when I was working on a boaters version. I had to use the Energizer Ultimate lithiums and reduce the amount of copper used in the heatsink. The new FTP version of the DEFT will have a less copper so it might work although I have yet to test it. I guess I should go do that.

 

[saabluster]

There is simply no way for a "small" flashlight to float and still look like a normal flashlight.

I wonder what effect filling the light with helium would do. Should help some and may make a light that is just on the verge of floating work. :shrug:

 

[Dude Dudeson]

I wonder what effect filling the light with helium would do. Should help some and may make a light that is just on the verge of floating work. :shrug:

I can say that this was thought of by Paul MacCready for solar powered aircraft - and he has built working ones. Google his name...

Anyway he and his team determined that the additional buoyancy of helium was more than offset by the extra weight required to properly seal it.

Helium tends to leech out of things much more so than air.

 

[Dances with Flashlight]

I wonder what effect filling the light with helium would do. Should help some and may make a light that is just on the verge of floating work. :shrug:

The Mythbusters did an episode on a helium filled football and its effect on throwing distance. That, however, seems different than this scenario. Even if a helium filled flashlight "weighed" less than one filled with air, it would make no significant difference. It would not cause the light to displace any more or less water, displacement being determined by volume rather than weight. A helium filled light, even if "weighing" less than one filled with air, would be at best a little more buoyant - but still not sufficiently buoyant to float... unless its overall size and volume were increased to displace enough additional water to overcome its weight.

 

[Dude Dudeson]

displacement being determined by volume rather than weight. .

This is incorrect.

Take a bowling ball and a styrofoam ball of the same size and toss them in water.

Displacement is a function of mass AND volume.

To get closer to your example, take two equally sized balloons, one filled with water and the other with air....

That said, the amount of helium you could fit in a battery filled flashlight would be way too small to make a real difference UNLESS the light was already very close to being able to float in the first place.

 

[Dances with Flashlight]

Should have thought of that myself.

 

[neal71]

Law of Flotation:
When a floating body like wood is placed in water, it sinks until the weight of water displaced by it is just equal to its own weight and then it floats.
Principle of Floatation:
A floating body displaces an amount of fluid equal to its own weight.

Floating and Sinking:
When an object is placed on the surface of a liquid it will either float or sink. This depends upon two forces:
The weight W1 acting vertically downwards, which is due to the gravitational pull of the earth, and
Upthrust or buoyant force acting vertically upwards, which is equal to the weight of the liquid displaced by the object W2.
You know that the weight of an object is the product of its volume and its density. Hence,
W1 = Volume of the object (V) x Density of the object (d1)
W2 = Volume of the liquid displaced (V) x Density of the liquid (d2)

 

[MattE]

27 replies to this question already ! ! !

You guys are really one of a kind :twothumbs

This forum ROCKS....:twothumbs :twothumbs :twothumbs

Cheers / Matt

 

[Dude Dudeson]

Floating and Sinking:
When an object is placed on the surface of a liquid it will either float or sink. This depends upon two forces:
The weight W1 acting vertically downwards, which is due to the gravitational pull of the earth, and
Upthrust or buoyant force acting vertically upwards, which is equal to the weight of the liquid displaced by the object W2.)

This is also incorrect.

There is only one force involved in buoyancy - gravity.

Any free object placed in any liquid will displace it's own weight, no more, no less. The object does this because of gravity, nothing more.

TECHNICALLY the object also has a gravitational attraction of it's own toward Earth, but Earth being around 65 sextillion tons of mass even a 1 ton object is essentially zero in comparison.

If the object is less dense than the liquid it will float, if it's more dense it will sink, but either way it WILL displace it's own weight.

There is no "upthrust" force in buoyancy. It is merely the failure of the object to displace it's equivalent VOLUME, because it is less dense than the liquid.

Wow talk about going OT, but it does shed some light (pun not intended) on the original subject.

 

[Mjolnir]

This is also incorrect.

There is only one force involved in buoyancy - gravity.

Any free object placed in any liquid will displace it's own weight, no more, no less. The object does this because of gravity, nothing more.

TECHNICALLY the object also has a gravitational attraction of it's own toward Earth, but Earth being around 65 sextillion tons of mass even a 1 ton object is essentially zero in comparison.

If the object is less dense than the liquid it will float, if it's more dense it will sink, but either way it WILL displace it's own weight.

There is no "upthrust" force in buoyancy. It is merely the failure of the object to displace it's equivalent VOLUME, because it is less dense than the liquid.

Wow talk about going OT, but it does shed some light (pun not intended) on the original subject.

You do realize that you are arguing about semantics, not physics, right? The buoyant force is commonly referred to as just that: a buoyant force. Whether or not it is actually caused by another force doesn't change the fact that it is referred to as a force. In physics, the net force acting on the object is mg-Fb, or the weight of the object minus the buoyant force, which is ρVg. Of course, this essentially ends up being what you said, as g is present in both forces. However, there wasn't anything wrong with how neal71 phrased it, since that is a traditional view of the concept.

 

[neal71]

This is also incorrect.

There is only one force involved in buoyancy - gravity.

Any free object placed in any liquid will displace it's own weight, no more, no less. The object does this because of gravity, nothing more.

TECHNICALLY the object also has a gravitational attraction of it's own toward Earth, but Earth being around 65 sextillion tons of mass even a 1 ton object is essentially zero in comparison.

If the object is less dense than the liquid it will float, if it's more dense it will sink, but either way it WILL displace it's own weight.

There is no "upthrust" force in buoyancy. It is merely the failure of the object to displace it's equivalent VOLUME, because it is less dense than the liquid.

Wow talk about going OT, but it does shed some light (pun not intended) on the original subject.

Unless you believe some minor laws of physics- for every action there is an equal and opposite reaction. An object could not remain afloat without an upward force.

That upward force is buoyancy: buoyancy- is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least seem lighter.

Also, wouldn't the object in question displace its total volume not its weight? Then if the weight of the object is less than the weight of the total volume of the displaced liquid, flotation occurs?

 

[elumen8]

I often float in water while holding onto a metal flashlight...but I believe its a function of my rather bouyant tummy as of late, which in reality is a reaction to the vast consumption of sugar cookies and potato chips that causes my mid-section to expand to god-awful proportions, thus displacing a larger volume of water, although increasing the magnitude of fat cells adding to my overall bouyancy, in turn defying the gravitational attraction of the Earth, thereby forcing me to the surface of the water with said metal flashlight in hand.

-JB

 

[RobertM]

By my calculations, a 6D Maglite will float without batteries and gives you about 85-100 grams to work with to power it (AA lithium cells, spacers, etc.).

I guess you could possible use a 6D Mag body, a 3D bulb, 3x Energizer e2 lithium AA cells in one of mdocod's 3AA>1D hold. Then you would need something really light weight to use as a 5D spacer and then solder a wire from the bottom of the 3AA holder to the tailcap spring. Just an idea.

FWIW, here are some weight specs for batteries:

Energizer Alkaline:
AAA - 11.5 grams
AA - 23.0 grams
C - 66.2 grams
D - 148.0 grams

Energizer Lithium:
AAA - 7.6 grams
AA - 14.5 grams
123 - 16.5 grams

-Robert

 

[Saint_Dogbert]

Unless you believe some minor laws of physics- for every action there is an equal and opposite reaction. An object could not remain afloat without an upward force.

That upward force is buoyancy: buoyancy- is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least seem lighter.

Also, wouldn't the object in question displace its total volume not its weight? Then if the weight of the object is less than the weight of the total volume of the displaced liquid, flotation occurs?

An object resting on a table is supported by a force equal and opposite of that exerted upon it by gravity. The 'equal and opposite' is the key - the net force is zero.

The same applies to an object in a fluid (liquid or gas). Whether an object floats or sinks, it will displace a volume of fluid equal to it's weight. This will exert a force perpendicular to gravity - the buoyant force. Whether or not this force is equal to the mass of the object determines if it will float or not. The fluid displaced by a sinking object will still exert this upward or buoyant force, it just isn't great enough to balance the force of gravity. The net force is in the favor of gravity, causing sinking.

An object cannot displace a volume of fluid with a mass greater than it's own, because this would cause the buoyant force to be greater than gravity, forcing it upwards until equilibrium is achieved. However, an object can displace a volume of fluid with a mass less than it's own - as above, this results in the object sinking.

 

[neal71]

An object resting on a table is supported by a force equal and opposite of that exerted upon it by gravity. The 'equal and opposite' is the key - the net force is zero.

The same applies to an object in a fluid (liquid or gas). Whether an object floats or sinks, it will displace a volume of fluid equal to it's weight. This will exert a force perpendicular to gravity - the buoyant force. Whether or not this force is equal to the mass of the object determines if it will float or not. The fluid displaced by a sinking object will still exert this upward or buoyant force, it just isn't great enough to balance the force of gravity. The net force is in the favor of gravity, causing sinking.

An object cannot displace a volume of fluid with a mass greater than it's own, because this would cause the buoyant force to be greater than gravity, forcing it upwards until equilibrium is achieved. However, an object can displace a volume of fluid with a mass less than it's own - as above, this results in the object sinking.

Equal and opposite, means there is an equal force acting in the opposite direction of the original force. Even when an object is at rest forces are still acting on it, unless I am mistaken, gravity=9.8m/s^2 (at sea level) the downward force acting on everything on earth. There is a an upward force and a downward force on everything, so the net is zero, but there is still a force keeping everything from traveling to the center of the earth.

Newton's First Law states that an object will continue at rest or in motion in a straight line at constant velocity unless acted upon by an external force.

Newton's Second Law: F=M*A (net force equals mass times acceleration)

Newton's Third Law states that all forces in nature occur in pairs of forces which are equal in magnitude and opposite in direction

If you push on anything, it pushes back on you. That's why if you lean against the wall, you don't just fall through it. The wall pushes back on you as hard as you push on it, and you and the wall stay in place. Same applies to a light sitting on a table, or floating.

Definition of Buoyancy: is the upward force that keeps things afloat.

Archimedes' principle states that a fluid will exert an upward force on an object immersed in it equal to the weight of the fluid displaced by the object.
The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least seem lighter.

I am getting this stuff straight out of one of my books, and notes from last semester, I was not trying to argue with anyone, just thought I would do what my professors always say, and "use the book".

I believe we are arguing the same point?

 

[divine]

You do realize that you are arguing about semantics, not physics, right? The buoyant force is commonly referred to as just that: a buoyant force. Whether or not it is actually caused by another force doesn't change the fact that it is referred to as a force. In physics, the net force acting on the object is mg-Fb, or the weight of the object minus the buoyant force, which is ρVg. Of course, this essentially ends up being what you said, as g is present in both forces. However, there wasn't anything wrong with how neal71 phrased it, since that is a traditional view of the concept.

I'm replacing my post with quoting Mjolnir's post, because he has summed up what I said in much less words. Sorry I didn't notice you beat me to the punch and very well put, too.

Thanks.

 

[Saint_Dogbert]

Sorry I didn't clarify

- I was agreeing with you, just trying to explain it in a slightly different way.

 

[neal71]

I figured, but I was unsure, so I decided I would explain what I meant. I love intelligent debates.

 

[EngrPaul]

Floating in water of course, not air or mercury... :nana:

 

[Mjolnir]

Floating in water of course, not air or mercury... :nana:

A flashlight floating in mercury would make a very neat picture. Mercury is over 4 times as dense as aluminum, so it should float easily, and a fair amount of the light would be out of the water.

Anyone want to risk their light and health to get a cool picture?