AMASE: Buoyancy – Guelph Physics
[Junior scientist Mara standing at laptop]
Mara: Hey, Mum, come check this out! These whales are taking naps on their tails!
Mom, Dr. Joanne O’Meara: So cool! Did you know that scientists think that’s because of density?
Mara: Really?
O’Meara: So, things sink and float based on their density compared to the liquid they are in. So, they think that whales, the sperm whales in those photos [photo of sleeping whales] have less dense material in their heads compared to more dense material in the tails.
[O’Meara holds up a stuffed whale to demonstrate]
O’Meara: So, they’re drifting along like this. Slowly they will turn so that the less dense material is up here and the more dense material is down here.
[snoring sounds]
Mara: He’s not actually sleeping!
O’Meara: Do you want to try it out?
Mara: Sure! How though?
O’Meara: Well, we can do an experiment.
Mara: Ok
[O’Meara picks up a container of Play-Doh and a Styrofoam ball]
O’Meara: We can make some whales out of Playdoh and we’ll put a Styrofoam ball in the head of one, a Styrofoam ball in the tail of one, and we’ll do one without any Styrofoam and we’ll see what happens when we put them in a tank of water. Alright?
Mara: Sounds good!
O’Meara: Let’s do it!
[whale sounds with text flashcard]
[Play-Doh whale is lowered into a bucket of water lined with aquarium rocks on the bottom]
[text flashcard]
[a second Play-Doh whale is lowered into the bucket, followed by a third]
[text flashcard]
[O’Meara and Mara reappear]
Mara: So, the whales nap with their heads up because the low-density oil is in their tails?
O’Meara: No, the low density oil is in their heads so their heads end up floating up to the top and the tails sink down to the bottom.
[Mara pours water from a glass into a second glass of water and oil]
Mara: Oh, that would make sense why oil floats on water.
O’Meara: Exactly. You can do that with oil and water and you’ll get the lower density oil floating on top of the higher density water. But we can do an even better demonstration of this. Do you want to do a full nine-layer density tower?
Mara: That sounds like so much fun!
O’Meara: Alright! Let’s try it out!
[O’Meara and Mara appear with nine glasses of various liquids before them and hold up a few for display]
O’Meara: Ok so we’ve assembled a collection of nine different liquids of different densities and we’re going to slowly pour them into the container and make our density tower. Ok. Let’s start with honey.
[Mara holds up a glass with honey and then pours it into a large glass vessel]
O’Meara: Ready, sweetie? Haha
Mara: That’s not funny!
[Fast motion shot begins with music (bensound.com) as text appears between O’Meara and Mara’s heads to describe each liquid being poured into glass vessel]
[Mara uses a baster to drop smaller amounts of each liquid into glass vessel]
O’Meara: Alright! There we have our nine layers density tower!
[O’Meara picks up the glass vessel]
O’Meara: We’re gonna let this sit for a few minutes and come back and take a look at it again and see if it has all settled into nice clear layers.
O’Meara: So, we’ve got our nine-layer density tower here which is looking pretty good, some slightly strange things floating on top, but I think it looks pretty good with the different densities of the different liquids.
[O’Meara picks up a small red foam ball and a die while Mara picks up a screw]
O’Meara: So, what we can do now is drop different items in and see where they sink to and that tells us what their density is compared to all the different liquids. So, what do you want to start with?
Mara: Ah … the screw
O’Meara: Ok, we’re gonna drop in a screw. Alright, let’s see where it goes.
[O’Meara holds up a rock]
O’Meara: This, how about this?
Mara: A rock
O’Meara: A rock, I think is probably gonna go
[Meara nods as she takes the rock from O’Meara and drops it into the glass vessel]
Mara: To the bottom
O’Meara: All the way to the bottom, ok
[O’Meara picks up the die and rolls it in her fingers before passing to Mara who drops it in the glass vessel]
O’Meara: What about a die?
Mara: I don’t know where that will go
[O’Meara holds up a cherry tomato before dropping it into the glass vessel]
O’Meara: How about we’ll try a cherry tomato!
Mara: I wanna eat it!
O’Meara: We’ve got more. Alright, we’ve got a few little beads here, we can try those
[O’Meara holds up the beads before dropping them into the glass vessel]
Mara: Oooh, I wanna put one in
[O’Meara holds up small red foam ball before dropping it into the glass vessel]
O’Meara: And we have like a Nerf ball
Mara: It’s very foamy
O’Meara: It’s quite light so I’m thinking its not going to go very far. Ah, it doesn’t even go under the top layer!
[still image of a density tower beside a flashcard of text listing items in it]
O’Meara: You can make your own density tower and drop different objects in and let us know how it goes!
[Mara holds a glass canister full of water and beads]
Mara: Here’s a fun floating and sinking toy you can try at home. All you need is two types of beads, some rubbing alcohol, some water and coarse salt. Watch this!!
[Mara mixes the contents of the canister]
O’Meara: So, as Mara mixes it up, the two liquids will combine to create a new mixture which has a density in between the two and what you see is the less dense beads go to the top of this new mixture and the more dense beads go to the bottom of the mixture.
[O’Meara points at contents of canister as Mara displays it]
O’Meara: But, as the mixture settles and the two liquids separate out again we get the rubbing alcohol back on the top and we get the salt water on the bottom and the two beads will return to the point in between because they have the density that is in between the rubbing alcohol and the salt water. Pretty cool, huh?
It’s awesome!
So, we’ll put the instructions on how you can make your own bead buoyancy bottle in the comments below.
[music plays]
O’Meara: Keep those science questions coming. If you want to get int ouch with us you can find us on Instagram, Facebook and YouTube. Thanks for watching
Mara: Thanks for watching Ask Me Anything: Science Edition!
[Mara waves goodbye]
Credits
Music: https://www.bensound.com
Sound effects: freesound.org
Sleeping sperm whales image:
free diver swimming over a pod sleeping sperm whales, Physeter macrocephalus, according to a study, sperm whales doze in the upright drifting posture for about 10 to 15 minutes at a time, Dominica, Caribbean Sea, Atlantic Ocean, photo taken under permit n°RP 16-02/32 FIS-5 Photographer: Blue Planet Archive FBA