would a box be heavy?

Question

if there was a box which weighed about1 kg and inside was a weight about 25kgs, but it was floating in the box (pretend), Would it increase the weight of the box?

Answer 1

The box would weigh 26 kg.

You can imagine, say, a 25 kg turkey (a really big turkey!) flying around in the box without touching the sides (I suppose the box would have to be pretty big, too!)

The reason you'd "feel" the weight of the turkey is that the turkey needs to exert a force against the air in order to stay aloft. That force eventually gets transferred from the air to the bottom of the box.

The same is true if you imagine a scenario with something other than a turkey. For example, suppose there's no air in the box? In that case, the 25 kg weight could stay aloft by shooting rocket fuel out of its bottom--but even then the ejected gases would collide with the bottom of the box and push downward on it, with exactly 25 kg-weight of force.

If you imagine a magical scenario in which the weight was able to stay aloft without exerting any downward force, then I suppose the box would only weigh 1 kg. But now you're talking about somehow shielding the weight from gravity, and there's no known way to do that.

Answer 2

Unless we do know how it floats, we can't answer this type or question.

Consider the box and the weight inside first. The total weight is 25 + 1 = 26 kg.

We attach the weight to a weightless thread and the other end of the thread is attached to the top of the box. The weight is now floating inside the box.

The total weight will be again 26 kg.

If you make the 25 float by exerting a force on the box then the total weight will be 26 kg.

Now consider this.

There is a hole on the top of the box and the thread is passed through the hole and the other end is attached to the ceiling of the building. Again the 25kg floats. But now the weight will be 1kg alone.


If you make the 25 float without exerting a force on the box then the total weight will be 1 kg.

Answer 3

YES, ABSOLUTELY.

SOMEhow that weight needs to be accounted for, and if the object is inside the box, (and we will assume that the box is enclosed on all 6 sides,) then to make it float, then the weight has to be at equilibrium:

That means that the force of gravity is pulling on the weight with about 250N ( g = ~10 m/s^2 ), and a second force is pushing BACK upward at exactly that much force, 250 N. Well, where's that force coming from? Somewhere INSIDE the box, including it's walls.

Floating in massless liquid? Then the force is coming from the floor of the box.

Hovering on a cushion of air, like a helicopter? Then the force, ultimately, gets transmitted from the floor of the box via the air in the box to the object.

Flapping it's wings like a bird? Same as the helicopter.

Hanging from a string attached at the top of the box? The force comes from the ceiling of the box.

Any real world example, (i.e. something that doesn't use the words "levitation," or "magic,") is going to follow the rules of equilibrium and require that the force on the object come from inside the box, thus requiring an equal and opposite force on the walls of the box to compensate: Newton's laws require it.

And that requires that the box weight 260N.

Interestingly, the Mythbusters just did PRECISELY this experiment:

http://dsc.discovery.com/fansites/mythbusters/episode/episode.html

Check out Episode 77: Birds in a Truck.

Answer 4

Depends on what you mean by:

"The weight of the box"...

If you mean the box itself, then the answer is no.
If you mean the box and it's contents, then the answer is yes.

It is a matter of perception!

If the object is "floating" (a VERY FUZZY term which is open to personal interpretation) then there must be a force equal and opposite to the force of gravity pushing against SOMETHING in opposition to the object (not weight BTW.)

Whether it is pushing against the box itself or it is a matter of displacement of the contents of the box all depends on how you define "THE BOX."

Does the box have a top on it?
Is the box considered to be "a closed container?"
Is the box considered to be "an open container?"
If we are talking about displacement -- is the box airtight i.e.; a SEALED container?

If we are talking about DISPLACEMENT IN A SEALED CONTAINER, isn't the displacement pressure equal in every direction (including upwards?)

If I get a box in the mail which registers 26 kg when I put it on a scale, is the BOX heavy or is something IN the box heavy?

This resembles my original puzzle:

"Would the WEIGHT of a sealed submarine (all hatches closed) with a parakeet sitting on the table of the crew's mess change if the parakeet flew off of the table while the bird was in flight?"

The answer of which was debated for MONTHS without resolution. This in spite of the fact that you know the precise physics involved in a bird's flight (as opposed to "floating in a box.")
.

Answer 5

no because if it was floating inside the box and you weighed it then the box would only weigh, the 25kg weight wouldn't be touching the weighing scales

Answer 6

Yes. If you can feel the 1KG weight in your hands and the 25KG are mysterially floating within the box, something would transfer. To have 25 KG flaoting some sort of forcefield is required and thus you would have the full 26KG in your hands.

Answer 7

Yes, even simply floating in air in the box, the mass would cause an equal, downward force on the air in the box which would act on the surface area of the bottom of the box.

Answer 8

floating in the box or not, the box would take the weight of everything, anything inside, so the box plus the stuff inside would weigh 25 + 1 = 26kg

Answer 9

definitely yes.

the weight you feel is the weight of the box + contents. gravity is acting on this box + contents. you're applying a force = weight of the box + contents to hold it up.

fyi, kg is mass not weight.....

try an experiment. take an empty plastic milk container. put it on a scale. what's the weight? fill it with water. does it weight more or less? place a half full glass jar of ? (say peanut butter or jelly or mayo or ketchup - you pick) in the water. does the milk jug + water+ jar weigh more or less?

Answer 10

I cant prove it but I believe the weight and mass would both increase to 26kgs. use a big ballon filled with a heavy gas...say Xe in a hydrogen atmosphere so it will float..ideal situation,,no thermal variations etc . The forces at the interface of the balloon would be balanced but that force has to be transfered (gravity acting on the balloon) to the bottom of the box.