... Or a fun expedition of volume, mass, density, floatation, global warming, and also how to float in a swimming pool.

You are watching: An ice cube floats in a glass of water. as the ice melts, what happens to the water level?

by Jared Smith


Archimedes" Principles:

Any floating object displaces a volume of water same in weight to the object"s MASS.Any submerged object displaces a volume the water same to the object"s VOLUME.


Mass / density = Volume

Melting ice cream cube

If you place water and an ice cream cube in a cup so that the cup is totally full come the brim, what happens to the level the water as the ice melts? does it climb (overflow the cup), stay the same, or lower?

The ice cube is floating, so based on Archimedes" principle 1 above, we understand that the volume that water gift displaced (moved out of the way) is equal in mass (weight) come the fixed of the ice cream cube. So, if the ice cream cube has actually a massive of 10 grams, then the fixed of the water it has actually displaced will be 10 grams.

We know the thickness (or compactness, load per unit) of the ice cream cube is much less than the of the liquid water, otherwise it wouldn"t it is in floating. Water is among the very few solids the is less thick than when in its liquid form. If you take a one pound bottle of water and freeze it, it will certainly still weigh one pound, but the molecules will have actually spread apart a bit and it will certainly be less dense and take up an ext volume or space. This is why water bottles expand in the freezer. It"s comparable to a Jenga tower. When you start playing it has a fixed number of blocks, but as friend pull out blocks and place them on top, the tower becomes bigger, yet it still has the exact same mass/weight and variety of blocks.

Fresh, liquid water has a density of 1 gram every cubic centimeter (1g = 1cm^3, every cubic centimeter fluid water will weigh 1 gram). Through the formula above (Mass / thickness = Volume) and straightforward logic, we know that 10 grams of liquid water would take up 10 cubic cm of volume (10g / 1g/cm^3 = 10cm^3).

So let"s say that our 10 gram ice cube has a density of just .92 grams every cubit centimeter. By the formula above, 10 grams of mass that has a density of .92 grams every cubic centimeter will certainly take up around 10.9 cubic centimeters of an are (10g / .92g/cm^3 = 10.9cm^3). Again, the volume the 10 grams that frozen water is more than the volume of 10 grams of its fluid counterpart.

The floating ice cube has a mass of 10 grams, so based upon Archimedes" rule 1, it is displacing 10 grams that water (which has 10cm^3 the volume). Girlfriend can"t squeeze a 10.9cm^3 ice cream cube right into a 10cm^3 space, so the remainder of the ice cube (about 9% that it) will certainly be floating above the water line.

So what happens when the ice cream cube melts? The ice cream shrinks (decreases volume) and becomes more dense. The ice thickness will increase from .92g/cm^3 to the of fluid water (1g/cm^3). Keep in mind that the weight will certainly not (and cannot) change. The mass simply becomes much more dense and smaller - similar to putting blocks earlier into their initial positions in our Jenga tower. We recognize the ice cream cube sweet 10 grams initially, and also we recognize it"s thickness (1g/cm^3), for this reason let"s apply the formula to determine how much volume the melted ice cube takes. The prize is 10 cubic centimeters (10g / 1g/cm^3 = 10cm^3), which is precisely the same volume together the water that was originally displaced by the ice cube.

In short, the water level will not readjust as the ice cube melts

Other oddities

Anchors away

Using this very same logic, there space some funny analogies. Take into consideration an aluminum watercraft in a swimming pool. If you placed a 5 gallon bucket full of 100 pounds of lead or some various other metal into the boat, the watercraft will obtain lower in the water and the furthermore displaced water in the pool will cause the pool level come rise. And based on Archimedes" rule 1 because that floating objects, it would increase by the volume of water equal in load to the 100 lb lead bucket. Water weighs 8.3 pounds per gallon, therefore the boat will displace second 12 gallons that water (12 gallons * 8.3 pounds every gallon = 100 pounds).

What would occur if you litter the bucket of command overboard into the pool? will the swimming pool level increase, decrease, or stay the same?

When us toss the bucket of command overboard, the swimming pool level goes under 12 gallons (the volume that water no much longer displaced through the weight in the boat). Yet when it enters the water, it will be submerged, so we now need to use Archimedes" rule 2 for submerged objects (it will displace a volume that water equal to the object"s volume). The water level will then go up by the volume the the command bucket, which is 5 gallons. So, the net difference is that the swimming pool level will go under by 7 gallons, even though the bucket is tho technically in the pool.

Just remember the mass and also density don"t matter for submerged objects. Volume is everything. Take into consideration dropping a brick of clay and also a brick of gold into a bucket. The yellow has an ext mass and is an ext dense 보다 the clay, however if both bricks room the same size, both will displace the same amount the water.

A sinking ship

Similarly, if her aluminum watercraft weighed 100 pounds, it would displace 100 pounds the water (12 gallons) once floating. However if the watercraft springs a leak and also sinks, the pool level would certainly decrease 12 gallons minus the volume of the aluminum in the boat. The boat"s volume (amount of space comprised the aluminum metal) would certainly be much much less than 12 gallons. In fact, based on the thickness of aluminum (.1 pounds/in^3), we can determine using our formula the the volume of ours 100 pound watercraft will be about 1000 cubic inches (100/.1 = 1000). There space 231 cubic inches per gallon, for this reason the boat is consisted of of around 4.3 gallons that aluminum (1000/231 = 4.3) and thus displaces 4.3 gallons that water when submerged, much much less than the 12 gallons that exact same aluminum displaced when floating. In conclusion, when our boat sinks, the pool level goes under by 7.7 gallons.


As one experiment, to fill a sink through 5 or 6 customs of water and note the water level. Next set a heavy glass down right into the sink if balancing it appropriate side increase (i.e., so the doesn"t pointer over and also fill with water). The water level will notably rise to do room for the empty glass and also you"ll note that it"s challenging to acquire the glass come sink while additionally it is upright. The heavy glass displaces a lot of water since of the heavy mass that the glass (Archimedes" rule 1), yet it quiet floats because of it"s low thickness (don"t forget about all the air within the glass). The glass will certainly feel lighter to you since of the buoyancy principle (the force of the displaced water pushing up versus the load of the thing displacing it). It will float perfectly in the water when the weight of the glass equates to the weight of the water it is displacing.

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Now lay the glass down sideways and also let the submerge in the sink. The water level will certainly be only barely higher than the initial level. It now displaces very tiny water because the glass has actually a very low volume (Archimedes" principle 2).

A marble in ice

Back come our original scenario, what if the ice cube had actually a tiny marble installed inside that it? once the ice melts, would the water level increase, decrease, or stay the same?

Let"s say we have the same ice cube as before (10g with a thickness of .92g/cm^3 and also volume of 10.9cm^3) and a 1 gram marble v a thickness of 2g/cm^3. Using the formula above, we recognize the marble needs to have a volume of .5 cubic centimeters (1g / 2g/cm^3 = .5cm^3). Clearly the marble would just sink if us tossed it in the glass because its thickness (2g/cm^3) is higher than water"s (1g/cm^3). And also we recognize when submerged it would certainly displace .5cm^3 of water (Archimedes" rule 2). But when installed in the ice cube, what happens?

Will the float?

First, we require to identify whether the ice cream cube will certainly sink or float currently that it has the marble in it. To execute this, we need to number out the merged density of the ice cube and also marble. We know that the ice cube has a mass of 10 grams and the marble has a fixed of 1 gram, for a merged mass that 11 grams. We additionally know that the ice cream cube has a volume that 10.9cm^3 and also the marble has a volume that .5cm^3, because that a linked volume that 11.4cm^3. Using the formula, we deserve to determine that the an unified density is .965g/cm^3 (11g / thickness = 11.4cm^3, or 11/11.4 = .965). In various other words, the small marble obviously rises the linked density, yet it"s still less than the thickness of water, for this reason the thing will absolutely float!