Why You Should Love Density | Will Grover | TEDxUCR

Summary

In this engaging talk, the speaker shares personal anecdotes about the scientific curiosity instilled by his scientist parents, leading to a fascination with density. He explains how density, a measure of mass per unit volume, can reveal hidden properties of objects, from distinguishing healthy from sick cells to identifying materials. The speaker's work at MIT and UC Riverside explores using density to detect diseases like malaria, assess the effectiveness of cancer drugs, and monitor environmental health. The potential applications of density measurements are vast, from medical diagnostics to environmental safety.

Takeaways

• 👨‍🔬 The speaker, a scientist, shares personal anecdotes about growing up as the child of scientists and how they conducted experiments on him.
• 🔬 The speaker demonstrates the concept of density through an experiment with two cubes that look identical but have vastly different weights, illustrating the importance of density in distinguishing objects.
• 🧠 Density is defined as mass divided by volume, and it provides more information than either mass or volume alone, which is crucial for understanding the properties of objects.
• 🌍 Density varies widely on Earth, from 0 g/mL for gases to 22-23 g/mL for the densest elements like osmium and iridium.
• 🎈 The density of gases like helium and air is used to explain why helium-filled balloons float, demonstrating density's practical applications.
• 🛠️ Density can be used to identify substances, as shown by the difference between aluminum and tungsten blocks, which look similar but have distinct densities.
• 🏺 The historical example of Archimedes using density to determine the composition of the king's crown is recounted, highlighting the age-old utility of density measurements.
• 🏋️‍♀️ Density measurements are relevant to health and biology, such as assessing body fat percentage and distinguishing between healthy and diseased cells.
• 🧬 The speaker's research at MIT involved using density to differentiate between healthy and sick cells, including those affected by malaria or cancer, showcasing density's role in medical science.
• 🐟 Current research at UC Riverside explores the potential of density measurements in zebra fish embryos as an early warning system for environmental toxins, indicating density's broader ecological applications.

Q & A

What is the significance of the two cubes in the speaker's story?

The two cubes, although identical in appearance, differ significantly in weight, with one being almost ten times heavier than the other. This demonstrates the concept of density, which is a key theme in the speaker's narrative about distinguishing between similar-looking objects.

How did the speaker's son react when he was given the two cubes?

The speaker's son was surprised by the difference in weight when he was handed the second cube, which was much heavier despite looking identical to the first one.

What property of the cubes is used to distinguish between a healthy and a sick cell?

The property that distinguishes between the heavy and light cube, as well as between a healthy and sick cell, is density. The speaker discovered that density can be used to identify differences in cells that are not apparent through size and shape alone.

What is the range of densities encountered on Earth according to the speaker?

The range of densities on Earth spans from 0 grams per milliliter for gases like helium to about 22 or 23 grams per milliliter for the densest elements, such as osmium and iridium.

Why does the helium-filled balloon rise when released?

The helium-filled balloon rises because helium is less dense than air. According to the principle of buoyancy, objects with a lower density than the surrounding medium will rise.

How did Archimedes determine if the king's crown was made of pure gold?

Archimedes determined the purity of the king's crown by measuring its density. He compared the measured density of the crown to the known density of pure gold. If the densities matched, it indicated the crown was made of pure gold.

What method did the speaker's team use to measure the mass of single cells?

The speaker's team used a suspended microchannel resonator, a tiny mass sensor similar in principle to a baby bouncer, to measure the mass of single cells. This device allowed them to determine the cell's density by measuring its mass in two different fluids.

How does the density of red blood cells change when infected with malaria?

When red blood cells are infected with the malaria parasite, they become less dense. The parasite consumes hemoglobin, which results in a less dense form, thus reducing the overall density of the infected cells.

What insight can be gained from measuring the density of cancer cells after drug treatment?

Measuring the density of cancer cells after drug treatment can reveal changes that indicate the cells' response to the drug. An increase in density post-treatment suggests the drug is affecting the cells, potentially serving as a screening tool for drug efficacy.

What potential application does the speaker suggest for density measurements in zebrafish embryos?

The speaker suggests that density measurements in zebrafish embryos could serve as an early warning system, akin to a 'canary in a coal mine,' to detect harmful chemicals in water or air by monitoring changes in the density of the embryos.

Outlines

00:00

🔬 Introduction to Density and Its Impact on Our World

The speaker begins by sharing a personal anecdote about his experience as a child of two scientists, who often conducted science experiments on him. He demonstrates the concept of density through an experiment with two cubes that appear identical but have vastly different weights, one being almost ten times heavier than the other. This leads to a discussion on how density, defined as mass per unit volume, can reveal hidden properties of objects. The speaker connects this concept to his work at MIT, where he explored the possibility of distinguishing between healthy and sick cells based on their densities, which was a breakthrough in his research.

05:01

🏺 Historical and Practical Applications of Density

The speaker delves into the historical application of density by recounting the story of Archimedes, who was tasked with determining the purity of a crown. Archimedes discovered a method to measure density without destroying the object by weighing it in water and air. This method is still in use today, as exemplified by the speaker's reference to a modern athlete being weighed underwater to calculate her density. The speaker then explains how density can indicate health conditions, such as body fat percentage, and sets the stage for discussing how this principle can be applied to single cells.

10:03

🧬 Measuring Cellular Density: A New Frontier in Biology

The speaker describes the challenges and methods used to measure the density of single cells, which are too small to be weighed on conventional scales. He introduces a suspended microchannel resonator, a tool developed at MIT, which uses the oscillation frequency of a tiny 'diving board' to determine the mass of cells. By measuring the mass of cells in two different fluids, the density of the cells can be calculated. The speaker discusses how this technology can be used to identify cells infected with malaria or to assess the effectiveness of cancer drugs by observing changes in cell density.

15:04

🐟 Density as an Indicator of Health in Zebrafish Embryos

In the final paragraph, the speaker shares recent research from his lab at UC Riverside, where they are studying the density of zebrafish embryos to detect potential toxins in the environment. He explains that changes in the buoyant mass, which is a function of density, can indicate the health of the embryos. The speaker envisions a future where density measurements could serve as an early warning system for environmental hazards, akin to a canary in a coal mine, providing a non-invasive method to monitor the safety of air and water.

Keywords

💡Density

Density is defined as mass per unit volume of a substance and is a key concept in the video. It is used to distinguish between objects that may appear similar but have vastly different properties, such as the two cubes shown in the script. The video explains how density can reveal hidden properties of objects, such as the difference between a healthy and sick cell, and is central to the scientific experiments discussed.

💡Mass

Mass refers to the amount of matter in an object and is one of the components used to calculate density (mass divided by volume). In the video, mass is mentioned as a fundamental property that, when considered alongside volume, provides insights into the nature of objects. The script uses the example of weighing objects in air and water to determine their density.

💡Volume

Volume is the amount of space that a substance or object occupies and is the other component, along with mass, used to calculate density. The video script illustrates how volume measurements are crucial for determining the density of objects, such as the cubes and cells discussed, which can appear identical but have different densities.

💡Archimedes

Archimedes was a Greek mathematician, physicist, and inventor, known for formulating the principle of buoyancy, which is central to the concept of density. The video references Archimedes' method of determining the density of an object by measuring its weight in water and air, which is a technique still used today.

💡Suspended Microchannel Resonator

The Suspended Microchannel Resonator is a scientific instrument used to measure the mass of tiny objects like cells. The video explains how this device works by oscillating and how it can be used to measure the mass of cells, which, combined with volume measurements, allows scientists to calculate cell density.

💡Health and Disease

The video script discusses how density measurements can be used to distinguish between healthy and diseased cells. For instance, it mentions how cells infected with the malaria parasite are less dense than healthy cells, and how changes in cell density can indicate a response to cancer treatment.

💡Cancer Cells

Cancer cells are abnormal cells that divide uncontrollably and can invade other tissues. The video uses the example of leukemia cells to show how density measurements before and after drug treatment can indicate the effectiveness of the treatment, even when mass and volume measurements alone do not show significant changes.

💡Zebrafish Embryo

Zebrafish embryos are used in the video as an example of how density measurements can be used to detect environmental toxins. The script explains that changes in the density of zebrafish embryos can indicate the presence of harmful substances, similar to how a canary was used in coal mines to detect dangerous gases.

💡Environmental Toxins

Environmental toxins refer to harmful substances that can cause damage to living organisms and their environment. The video script discusses how changes in the density of zebrafish embryos can be used as an indicator of exposure to environmental toxins, highlighting the potential for density measurements in environmental monitoring.

💡Epiphany

Epiphany in the video refers to a sudden and striking realization or insight. The script describes the speaker's son's reaction to the heavy cube as an 'epiphany', illustrating how the concept of density can lead to profound understanding and new perspectives on the world.

Highlights

The speaker and his wife, both scientists, conducted science experiments on their children, including a demonstration with two cubes of different densities.

One cube was almost 10 times heavier than the other, despite their similar appearance.

The property that made one cube heavier was the same property found in cells to distinguish between healthy and sick cells: density.

Density is defined as mass divided by volume, providing more information than either mass or volume alone.

The range of densities on Earth varies from zero grams per milliliter for gases to 22-23 for the densest elements.

Density can determine whether an object floats or sinks, as illustrated by the helium balloon example.

The difference in density between aluminum and tungsten is what caused the surprise reaction to the two cubes.

Density can be used to identify the chemical composition of a material, as demonstrated with the cubes.

Archimedes used the principle of buoyancy to determine the density of the king's crown, a method still used today.

The speaker's team aimed to measure the density of single cells to distinguish between healthy and sick cells.

A suspended microchannel resonator was used to measure the mass of cells, inspired by the frequency principle of a baby bouncer.

Cells have a density between 1.0 and 1.2 grams per milliliter, with variations indicating different states or conditions.

Malaria-infected red blood cells were identified as less dense than healthy cells.

Cancer cells' response to drug treatment could be observed through changes in their density.

Density measurements of zebra fish embryos could indicate the presence of harmful chemicals in the environment.

The speaker envisions density measurements as a tool for early detection of environmental hazards, like a modern canary in a coal mine.

Density is a physical property that can reveal new perspectives on the world when measured accurately.

Transcripts

all right you know as he mentioned my

wife and I we met in Berkeley and we're

both scientists and one of the kind of

Occupational hazards of being the child

of two scientists like me and my wife is

that your parents like to perform little

science experiments on you from time to

time and uh I'll show you a couple of

those today uh if you'll let me and I'll

demonstrate one of them first this one I

did a few days ago with my son it

involved these two cubes shown here you

can see that they're similar size

similar shape similar colors to them

right and I handed the first one to my

son thle fine into his hand and he was

like okay Dad what are you doing and I

handed the second one to him thle and he

went whoa jeez and to prove it to you we

took a little photo of him like using a

little Teeter titer with them what he

realized was that the one on the right

there even though identical to the other

one is tremendously more heavy than the

first one it's almost 10 times heavier

if any of youall don't believe me after

the show tonight you're welcome to come

up and lift these for yourself it's not

the kind of thing that makes a good

visual demo but trust me and so he send

that and in looking at these cubes he

realized that a whole new window had

opened up on the World to in some way

that you could have two objects that

look so similar to each other in every

describable way and yet when you feel

them when you pick them up you can tell

something's wrong something's very

different about this one versus this one

what is that thing what is this like

secret invisible world of objects that

we've never seen before this point I

loved watching him have that kind of

little Epiphany because it was really a

lot like what I had about five or six

years earlier I was a postto at MIT at

the time and I was in a lab where we

were trying to measure single cells and

in particular trying to see is there any

way you could tell the difference

between a healthy cell and a sick cell

based on these measurements and you know

just like these cubes often these cells

would look very similar to each other in

terms of their size and their shape and

their appearance and we needed to find

ways properties of these cells that you

could measure and use to distinguish a

healthy cell from a sick cell what could

that be well turns out in the story I'm

here to tell you tonight is that the

very property of these two cubes that

makes one so ridiculously heavy and the

other one feels so light the very

property of these cubes is the same

property we found of living cells that

lets us tell whether a cell is sick or

healthy and that property is density you

remember density right if you're like I

was five or six years ago you learned it

in high school and hadn't thought much

about it since then right well hopefully

by the end of tonight I can show you why

it's the most awesome physical property

and you should really appreciate and

love density uh so you might remember

that density is the function of two

other physical properties of an object

namely their Mass how much an object

weighs and its volume how much space a

little object occupies and you'll agree

that both of those measurements mass and

volume they're just ways of telling you

how much of an object you have how big

is it but when you divide the two by

each other when you take the mass and

divide it by the volume you get the

density and that's a whole other thing

it tells you so much more than either of

mass or volume can tell you on their own

I'll try to give you a few examples of

that today so first we're going to talk

about density for a few minutes we might

as well acquaint ourselves with the

range of densities that we encounter

here on Earth they range from zero grams

per milliliter all the way up to about

22 or 23 for the most dense elements

osmium and aridium and so we can look at

a few spots on this little number line

and see what the densities of a few

things are on the far left hand side

here we see the density of gases like

helium point 00002 G per Miller and air

0013 G per Miller these are all very low

densities but you notice helium is just

a little less dense than air and that is

why when we fill a balloon with helium

and let go of it it goes up so this sort

of the first example of density giving

us something meaningful in our

interpretation of the world around us in

this example what determines when I let

something go whether it goes down or up

it's density if it's more dense than

what's around it it'll go down if it's

less dense than what's around it like

the balloon it'll go up so a little

example of density telling us something

about the world around us let's go up

the scale a little bit further around

2.7 we encounter aluminum Nice metal and

then way up at 19.2 on the density scale

we encounter tungsten and that is what

these two blocks are made of and that

difference the difference in density

between 2.7 aluminum aluminum can very

light and tungsten one of the densest

elements uh that's known uh is the

reason why my son reacted to these and

being so different and so there's

another Insight that density can give us

I could walk up on those on these blocks

and by looking at them I couldn't tell

you which is tungsten and which is

aluminum but if you let me pick them up

and if I know these density numbers then

it's very easy for me to tell that this

is tungsten and that's aluminum so here

density a physical property is giving us

a way to identify chemically what

material an object's made of pretty neat

that idea of using density to identify a

substance is not an old not a new one in

fact over 2,000 years ago Archimedes was

asked in the story by the king to

determine whether one of the king's

crowns was made of pure gold or not and

so Archimedes was a smart man and he

realized if he could measure the density

of the crown and compare that to the

known density of pure gold which is 19.3

very dense if they equaled then it

proved that the crown was made of pure

gold but if they were different it meant

that the king had been swindled by the

crown maker I guess and so by measuring

density he knew he could easily tell the

difference between pure gold at 19.3 and

something like iron pyite fools gold at

5.0 but Archimedes face a challenge how

do you measure the density of an object

like a crown right I told you density is

mass divided by volume now getting the

mass of the crown is easy enough you

just weigh it but how do you measure the

volume of the crown without destroying

it or melting it down in a way he needed

a way to measure the density of the

crown without destroying it what he came

up with was really one of the most I

think brilliant experimental ideas in

the history of Science and this is what

it is he realized that he could weigh

the crown underwater if you've ever been

in a pool you know you weigh a little

less under water than you do standing on

dry land right well how much less do you

weigh well the way the math works out

the amount that different that you weigh

in the water is a function of two things

the density of the water which is one we

know that and the density of youu the

object that we're weighing or the crown

so if we weigh an object like a crown in

two different fluids in this example in

water and air from those two weight

measurements we can calculate the

density of the crown that's exactly what

Archimedes did and he was able to

determine what the crown was made of so

now amazing ly 2,000 years later we

still do exactly what Archimedes

described so long ago in this example

this athlete here is being weight

underneath the water and by combining

that measurement with the second

measurement of her weight on on dry land

we'd be able to calculate her density

why do you need to know a person's

density Well turns out along with

telling you what a cube is and all these

different things it can tell you if

you're fat or thin uh you've heard the

expression fat floats and it does if you

have a lot of fat in your body that

reduces your net density down to about

1.0 1 or so if you have a lot less fat

bone and muscle and things are more

dense so that makes your body more dense

and you reach about 1.07 or 1.08 so

here's our first example of density

remember a physical property telling us

something very biological very health in

nature in this case how fat or how thin

a person could be all from density so

back five or six years ago as a postto

we looked at this and saw all the things

density could tell you and we had a

thought what if it worked just as well

on single cells what if just just like I

could measure the density of a human

body and tell things about the health of

the body could I possibly measure single

cells and infer things like the

difference between a healthy cell and a

sick cell or a cancerous cell based on

this density measurement so we set out

to try to do that and the first

challenge was what we need to measure

the density of a cell which hadn't

really been done before and we realized

we could use the method that Archimedes

described the idea of weighing it in two

fluids of different density but how do

you weigh a cell you might first turn to

this if it's in your your your kitchen

uh but but I can tell you cells are a

whole lot too small to weigh on this and

and Tiny living cells don't take too

kindly to being plunked down onto a

little kitchen scale so we needed a way

to measure the extremely tiny mass of

cells in order to figure out what their

density was how do we do that well

luckily the lab I joined as a as a

postto already had a little MTH sensor

that they worked on that was perfect for

this job and to explain to you how it

works I'll show you another experiment I

performed on one of my children uh this

this is Jack he's uh a little jerky up

there but he's a lot smoother than that

in real life Jack is it looks like he's

on a baby bouncer and he is on a baby

bouncer but it's also a sophisticated

mass sensor believe it or not you see

the frequency at which he's bouncing up

and down as he kicks his legs there he

can't just control that frequency it

will that's actually a fixed frequency

it's a function of a few things that

determine it but crucially it's a

function of his Mass so if he were to

say sit there and eat a hamburger uh

that frequency would slow down because

his Mass would have gone up that's how

it works so my wife and I again in this

in the spirit of experimenting on our

children realized we had an unexpected

mass sensor here and we decided to

calibrate it first so we put some

weights of known weights on it uh from

our weight set ranging from this is

perfectly normal ranging from 5 PBS

which had the highest frequency of

oscillation 149 beats per minute all the

way to the highest weight 20 pounds on

the bouncer which had the slowest

frequency of oscillation only 88 beats

per minute now that we've calibrated it

like a good scientist if you're if

you're preparing lab notebooks for of

your lab courses remember got a good

calibration curve show my data Etc

you've done you calibrated our mass

sensor now we're able to put jack back

in it and measure his frequency and

determine what his weight is 20 pounds

and then do the same for his identical

twin brother Henry and see that he has a

slightly lower frequency which means he

has a slightly higher mass and indeed

that's exactly true so here you see uh

this sensor is so fantastic we have a

baby bouncer that's capable of

distinguishing two identical twins from

each other even I can't do that most

days and I'm their father

so this measurement principle is really

quite good uh as a way to weigh

something it turns out you'll never look

at a baby bouncer again the same way I

hope so here's the here's the point if

you take that baby bouncer and scale it

down I mean way way down so that the

bouncing part is about the size of a

human hair at that point you're able to

put a cell on it instead of Jack or

Henry and do the same measurement and

weigh them and that's what this tool

here does this was developed at MIT in

the lab before I joined it they call it

a suspended microchannel resonator and

at the heart of it is a tiny little

bouncer a little diving board shaped

thing that you can see here and it

oscillates like that if we look inside

of it we don't actually put the cells on

the outside of it we Slide the cells on

the inside and this little blue Channel

shown there if you zoom in on it that's

the sensor it's oscillating and when we

send a cell like this little red blood

cell through we weigh the cell basically

so by measuring two cell masses and two

fluids of different density we can

calculate the density of the cell long

story short so there that's how we do it

what is the density of a cell after all

that is this even interesting and what

we found we've measured a bunch of cells

and we found that most cells have a

density between 1.0 and 1.2 gram per

Miller and on one hand that's not too

surprising because water has a density

of 1.0 and cells are mostly water so it

makes sense that we would see values

around that number but not all cells

have the same density and I'll give you

just a few examples tonight of how the

density of a cell can be used to

determine something very interesting and

get some insights about the cell here's

the first example this plot here shows

each black dot is the measurement of a

single red blood cell from someone's

blood on the bottom you can see what the

density of those cells are ranging

around 1.10 1.12 on the side here you

can see the weight of each of those

cells in picograms if you don't know

picograms or wonder how much a cell

weighs a millionth of a millionth of a

gram very very small weights and so in

healthy blood cells we can see all of

those measurements kind of pile up into

that little oval region that's where we

expect them to go but if you do the same

measurement on cells that part that some

of them are infected with malaria

parasite uh we see a few cells over

there to the left that are a little less

dense than the healthy cells those are

the cells that are infected with malaria

it's been known for a while that the

little parasite that is malaria eats up

the hemoglobin in your red blood cells

turns it into a form that's less dense

and the result of that is an infected

cell becomes less dense and we can see

that and we can identify the infected

cells compared to the healthy cells

based on their density what else here's

data showing the mass and volume of

cancer cells these are leukemia cells

from a mouse and you're seeing in the

black points the measurements before we

treat them with a drug and in the red

points the measurements after we treat

them with an anti-cancer drug and if you

look just at the mass and volume of the

cells before and after black and red you

don't see much of a change and in fact

if this data was all you had to go by

you might not have thought that drug was

any good but like I said density is mass

divid by volume if you do that math for

each one of these points you get this

story over here a very much clearer

picture we see that after treatment just

minutes after we dose these cells with a

drug we see that uh a large number of

the cells have increased in their

density by a large statistically

significant amount what this means is

that just minutes after treating these

cells with a drug we can see that yeah

those cancer cells are reacting to that

drug we hope that eventually this could

become a drug screening tool you might

be able to use that density change as a

way to find new cancer drugs based on

whether or not the cell's density

changes when they encounter the drug

and then I can finish with just a little

uh recent data from my lab here at UC

Riverside this is showing the buoyant

Mass which is a function of density of

single zebra of a single zebra fish

embryo why we're studying zebra fish

well a few reasons uh zebra fish embryos

are an aquatic organism and so if

something hurts a zebra fish embryo like

a chemical then there's reason to think

that it would hurt a lot of other fish

and it's probably the kind of chemical

you'd want to not have in your waterways

and two a zebra fish embryo looks a lot

like a human embryo so so if something

hurts a zebra fish embryo there's a good

reason to think that you wouldn't want

to have it around any of your embryos

either so this is what the mass buoyant

mass or density of a healthy zebra fish

looks like over time and then if we do

the same measurement on a sick zebra

fish that we've exposed to some chemical

that makes it ill we see a very

different reaction we see little

decreases in its buoyant Mass it means

its density is changing we don't know

what's causing this yet but what we do

know is that we've tried the same

experiment on a whole bunch of different

sorts of sicknesses different sorts of

toxicants for these zebra fish and we

still see the same signature it's as if

this change is somehow indicative of of

of a sick zebra fish regardless of

exactly what we did to make it ill and

so where we want to see this going in

the future is you're familiar with the

idea of a canary and a coal mine right

uh the the the bird that the coal miners

brought down to see if the air was safe

to breathe we hope that the density

measurements that we're making right now

will in the future become like a sort of

super Canary in a coal mine that by

measuring the density of these organisms

of these embryos or or other

microorganisms we could have an

instrument that will live and Sample the

groundwater and tell you if there's

something dangerous entering into it or

an instrument that can live in the air

and Sample the air around us and tell us

if there's something dangerous all based

on how the density of these organisms

react to exposure to whatever is in the

environment that's one direction we're

taking it so hopefully today I showed

you and shared with you why I think

density is just the most awesome

physical property that's out there it's

something that every object around here

from crowns to cell to fish to you and

me we all have a density we can't see it

but we can feel it and we can measure it

and if you can measure it accurately

enough you can use it to sort of open up

whole new views on the world around you

thank

[Applause]

you