[Intro sound with Guelph Physics logo on screen]
[Cut to girl in the kitchen]
Mara: Hey mom come check this out! These whales are taking naps on their tails.
[Woman enters the frame]
Joanne: So cool! Did you know that scientists think that's because of density?
Joanne: So things sink and float based on their density compared to the liquid they're in so they think that whales, the sperm whales in those photos, have less dense material in their heads compared to more dense material in their tails.
[Image of sperm whales overlays video]
So if they're drifting along like this slowly they will turn so that the less dense materials up here and the more dense materials down here.
[Joanne indicates with a stuffed whale the head facing up and the tail facing down.]
Mara: He's not actually sleeping.
Joanne: Do you want to try it out?
Mara: Sure! How though?
[Joanne brings Play-Doh and Styrofoam ball from the counter into view]
Joanne: Well we can do an experiment. We could make some whales out of Play-Doh 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!
Joanne: Let's do it.
[Video Transition - Whale A: Styrofoam head]
[Video focuses on a tank with water, water sounds]
[Hand puts whale figure into the tank and it floats with its head pointing up, just breaking the surface of the water.]
[Video Transition – Whale B: Styrofoam tail]
[Video focuses on a tank with water, beach sounds]
[Hand puts second whale figure into the tank and it floats with it’s tail pointing up, just breaking the surface of the water.]
[Video Transition – Whale C: All Play-Doh]
[Video focuses on a tank with water, beach sounds]
[Hand puts third whale figure into the tank and it sinks to the bottom of the tank.]
[Video cuts back to Joanne and Mara sitting at the kitchen bar.]
Mara: So the whales nap with their heads up because the low density oil is in their tails?
Joanne: No the low density oil is in their heads so their heads end up floating up to the top and their tails sink down to the bottom.
Mara: Oh that would make sense why oil floats on water.
[Mara pours oil from a jar into a glass of water]
Joanne: Exactly. So you can do that with oil and water and you'll get the lower density oil floating on top of the higher density water.
[Mara holds up glass with separated oil and 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.
Joanne: All right let's try it out!
Joanne: Okay 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.
[Joanne and Mara show glasses and jars of various liquids]
Okay let's start with honey. Ready sweetie?
Mara: That's not funny.
[Music plays, video speeds up. Mara adds liquids into the container; honey, corn syrup, maple syrup, milk, dish soap, water (with food colouring), vegetable oil, rubbing alcohol (with food colouring), lamp oil]
[Joanne holds container up]
Joanne: All right there we have our nine layers density tower. We're gonna let this sit for a few minutes and come back and take a look at it again and see if it's all settled into nice clear layers.
[Video cuts to a few minutes later]
Joanne: 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. The different densities of the different liquids so what we can do now is we can 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: Um, this screw.
Joanne: Okay we're going to drop in a screw. All right let's see where it goes... let's... how about this.
Mara: The rock?
Joanne: Rock. I think probably going to go all the way to the bottom okay. How about a die?
Mara: I dunno where it'll go.
Joanne: We'll try a cherry tomato.
Mara: I want to eat it.
Joanne: We got more. All right we got a few little beads here we can try those. All right we have a uh like a nerf ball.
Mara: It's very foamy.
Joanne: It's quite light so I'm thinking it's not going to go very far. It doesn't even go under the top layer.
You make your own density tower and drop different objects in and let us know how it goes.
Mara: Here's a fun floating and sinking toy you can try at home.
[Mara holds up a tall glass container with clear liquid and beads suspended in the center of the liquid]
All you need is two types of beads, some rubbing alcohol and some water and coarse salt.
Joanne: 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 new mixture. 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?
So, we'll put the instructions on how you can make your own bead buoyancy bottle uh in the comments below.
[Music plays as Joanne and Mara watch the beads settle back to the center of the container.]
Joanne: Keep those science questions coming. If you want to get in touch with us you can find us on Instagram, Facebook and YouTube.
Mara: Thanks for watching Ask Me Anything: Science Edition!
Dr. Joanne O'Meara and junior scientist Mara are looking at buoyancy, in all it's forms.
Got a question for our team to answer?
We're doing what we can here at Physics, University of Guelph to help out educators right now. Do you or your students have fun science questions you'd like to explore?
Hit us up on FB or IG and we'll throw together a fun video response for you! Any grade level, any subject, the zanier the better! We look forward to hearing from you!
Make your own Buoyancy Beads Bottle
- a clean/empty clear plastic bottle and cap (500 mL to 1 L works well)
- distilled water (available at grocery stores, Walmart, etc.) – enough to fill a little less than half the volume of the bottle you are using
- coarse salt/pickling salt
- isopropyl alcohol/rubbing alcohol (90% purity or higher) – enough to fill a little less than half the volume of the bottle you are using
- 50 to 100 Perler beads (available at craft stores, Walmart, etc.)
- 50 to 100 Pony beads (available at craft stores, Walmart, etc.)
- Use some of the distilled water to rinse out the bottle to make sure it’s clean.
- Mix the distilled water and coarse salt together, stirring to get all of the salt dissolved. You will need about 8 teaspoons of salt for every 250 mL of distilled water. Add the saltwater mixture to your bottle.
- Pour in an equal volume of 90+% isopropyl alcohol. It looks cloudy at first but that’s ok! Put the cap on and mix the contents then set it down to rest. You will see the two solutions separate as it settles.
- Open the lid and add the Pony beads. They will settle at the boundary between the two liquids. Now add the smaller Perler beads for approximately equal layers of each type.
- HAVE FUN!!!!