Density is basically how tightly packed atoms are. (Mathematically, density is mass divided by volume.) For example, take a golf ball and a ping pong ball. Both are about the same size or, in other words, take up the same volume.

However, one is much heavier, has more mass, than the other. The golf ball has its atoms much more closely packed together than the ping pong ball and as such the golf ball is denser.

These are quick and easy demonstrations for density that use simple household materials:
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34 Responses to “Quick & Easy Density”

  1. You’ll want to use something with an optical index close to pyrex.

  2. arrowmakercpi says:

    What if I don’t have vegetable oil?

  3. You don’t have to use alcohol and honey, but you want to use as many different liquids as possible so you can see the difference in their density. I recommend using at least three different liquids.

  4. Do you have to use alcohol and honey?

  5. Hi Melissa! So happy you are enjoying the content! And yes, you can get plastic or inexpensive glassware from

    I wish you lived nearby so I could give you some of the glassware the university donated to me five years ago (they completely redid ALL their chemistry labs, and since the technician and I are friends, she gave me huge boxes of used glassware that I’ve been giving away to local students here, but I still can’t seem to give it away fast enough to clear out our warehouse space!)

    Anyhow, Unit 8 has a basic all-in-one-set that you can get that includes most of what he’ll need until high school from Home Training Tools.

  6. Melissa Heath says:

    Hi there! Not sure THIS is the right place for the question, but it’s all I could find. My son just started doing Unit 3 and he loves it so far. And *I* love how most everything you need for experiments is common household items, however my son is a big science nerd and wants to get his hands on some basic chemistry lab supplies. Since we have a budget, I can’t buy all the wonderful things we see. Do you happen to have a list somewhere of the basic essentials you would need to start out in chemistry? I’m looking at a science supply website right now and they have SO many sizes of beakers and graduated cylinders that I am lost. Thanks!

  7. Water expands when it freezes, which is why icebergs float. Water gets more and more dense as you cool it, and gets a max density at 4 degrees C (which is why lakes freeze on the top first). The reason why water expands when it freezes is because the water molecule has a big hole the middle of it. It looks like a big hexagon with a hole in the center, and when these hexagons join together like a honeycomb, they take up more space than in their liquid state.

  8. Laura Swick says:

    And why does cooling make water less dense? You said cooling took away energy out of the atoms so they pack tightly but
    ice expands and floats on water.

  9. Angela Hillier says:

    I have an idea what happens if you close the jar and shake it will the layers mix up or not?

  10. Ahsan Nuri says:

    thanks for making logging in and out easy

  11. You can check to make sure that the hot water is hot, and the cold water is very cold. The temperature differences should help the two stay separate once you remove the index card or paper.

    As for the red dye, it mixes quickly with the hotter water because at hotter temperatures, the molecules are more agitated and move around quickly. This means there is more space between them and the dye can fill those spaces more easily. When the water is cold, this will take longer because the cold water’s greater density means that there is less space between those molecules for the dye to work through.

  12. Keith Burge says:

    We did the hot and cold swirl experiment and seemed to get the wrong results. We put blue food coloring in the hot water and red in the cold. The blue took longer to reach the bottom than the red and it seems like it should be the other way around since the cold water is denser. Also when we inverted the cold water glass on top of the hot, they just mixed together and turned purple. We didn’t notice anything happening. What did we do wrong?

  13. As you probably know, soap is useful for cleansing because it is an emulsifying agent – it makes it possible to mix liquids that are immiscible (un-blendable), such as water and oil (see Wikipedia’s “Emulsion” page for more details). If the soap, water, and oil were poured very carefully into the jar one at a time so that they all sat separated, it’s likely little to no emulsion would occur. However, if the combined ingredients were agitated perhaps by swirling the mixture or stirring it with a spoon, the soap would gradually dissolve into the water and oil and cause them to emulsify as you suggested.

  14. Will the soap emulsify the water and the oil?

  15. It sounds like you did this correctly. Since yellow and green are close in the rainbow, it can be hard to tell the difference between them. Eventually you will find that they both mix together, but it’s how they mix in the beginning that’s the most interesting. The cold should have stuck together more and been slower to mix, while the warmer one will diffuse out more rapidly and mix. Is that what you found?

  16. Helen Megennis says:

    We did the hot and cold swirl and we used yellow and green when we flipped the glasses on top of each other the hot green would turn all the yellow green. Then we changed the colors so the cold was green and hot was yellow we then flipped them again and the green once again. Was this supposed to happen?

  17. The alcohol’s chemical bonds are very strong, too strong for water to break apart. The alcohol is perfectly happy staying with its own family. Alcohol and water molecules will bond, but for a very short time. The bonds between alcohol and water molecules quickly break due to the weakness of the bond between the water and alcohol molecules. Because they don’t bond well, then density of the separate liquids comes into play. The least dense liquid, rubbing alcohol, will stratify on top of the denser water layer.

  18. texasmama says:

    Why doesn’t rubbing alcohol mix with water? we tried it and nothing happened. The rubbing alcohol had red food dye in it. We tried it separate in a cup with water and in the glass jar with all the others. In the jar the rubbing alcohol did go to the top and the oil separated it from mixing with the water.

    Thanks , Texas daughter.

  19. Water is a liquid, and the molecule is two hydrogen and one oxygen. You can have water as a gas if you heat a pot of water into steam – then you have a cloud of water vapor, which is less dense than the liquid state (unless you capture it and put it under pressure…) You can read more about this in Unit 13 on Thermodynamics.

  20. Julie Kuehler says:

    Is gas more dense than water.


  21. Sandra Killough says:

    To Cheri and your question about the water not freezing outside, but then freezing inside…did you remove the cap? If the water is under pressure outside it may not freeze. If you take it inside, but don’t remove the cap, it should still stay liquid, but as soon as the cap is removed, the pressure is relieved and you can see ice crystals grow very quickly. I live in Wisconsin and we did this (by accident) last year with some apple juice. Very cool, but we didn’t get to have it with our breakfast!

  22. Great question! It’s not only the gas molecule size/weight, but also how many molecules are packed into one spot at a time (density, which is related to pressure). For example, if you strapped pieces of cardboard to your arms on Saturn’s moon Titan and flapped, you’d fly. The nitrogen atmosphere is thick enough to support your weight. However on Earth, the atmospheric pressure of nitrogen is lower, and we can’t do this.

    The denser the atmosphere, the more molecules you need to shove out of the way and the slower your flight speed. Near sea level, the atmosphere is thicker than at the top of a mountain. Pilots need to adjust for this when they are flying airplanes on mountaintops or extremely warm days.

  23. Toni Stirtz says:

    We don’t know where to ask this question so we thought we would just ask it here. My son Jonathan wants to know what is the heaviest gas and would an airplane fly faster or slower in a gas heavier than air? Thanks.

  24. Carolyn Norville says:

    I could not see the other stuff you put in because, I thought they were mixing together but, still ccccoooolllll!!!!!

  25. Cheri Blomquist says:

    Cool. Thanks, Aurora. 🙂

    Annika Blomquist

  26. Wow – that is really strange. I have a colleague who’s an expert in thermodynamics (temperature, pressure…) – I’ll ask and see what he thinks.


  27. Cheri Blomquist says:

    This doesn’t really have anything to do with this experiment, but I didn’t know where else to ask. We get these big jugs from Cub where we refill our water, since our tap water isn’t good. Today, my dad got water and was carrying it into the house. Now, I live up here in MN where it is below freezing right now. When the water jugs were outside where it was cold, the water didn’t freeze. But when my dad brought it inside, it froze. Even though it is warm inside. I was wondering, how come the water didn’t freeze outside, but it did freeze when it got inside? Sorry this is so long, but I just don’t get it. 🙂

    Annika Blomquist

  28. You can try it yourself… and yes, given enough time, it will separate. Try putting it into the fridge or freezer after it’s stratified and see if any of the layers swap positions.

  29. Sonya Fiebig says:

    Hi Aurora

    I was wondering, if you were to shake up the jar, would it again settle into those layers?

    Laura Fiebig

  30. Cara Combs says:

    In discussing states of matter, and weights of gasses in particular, we discussed that helium balloons float because the helium weighs less than the other gases in our air. We happened to have a stray balloon from a birthday party, so instead of climbing on a chair to get it, I let the kids shoot it with a water bottle. As the water accumulated on the balloon, it slowly sank. They were delighted to see that drying it off with a towel removed the excess weight and allowed it to float again. Anyway, it’s super simple, and we often have party balloons on hand, so I thought I’d share.

  31. Deanna Betts says:

    We did the density jar and it turned out well. We tried the hot and cold swirl twice. The cold water color spread out slowly and the hot water color spread out fast. When we tried to combine them- it made a mess. The second time it created the color purcple. Martin

  32. Debra Thomson says:

    How long does it take for the Density Jar to settle?

    Holly Thomson

  33. Debra Thomson says:

    This is SO cool!

    Holly Thomson