Fun fact: if you make two cups of coffee, one with milk and one black, which will cool faster?
Counterintuitively, the black coffee cools off FASTER.

(Yes adding cold milk 🥛 to hot coffee ☕️ does cool it off somewhat but the question is about the RATE of cooling. Also the ☕️ will reach room temperature first.)

But WHY is this?
Buckle up for some cool morning physics!
There are two reasons:
1. Dark objects radiate heat faster (this has to do with the Stefan Boltzmann law & black body radiation)
2. Viscosity slows down evaporation (milk/cream thickens the coffee; evaporation is an important mechanism of cooling)

We’ll talk more about each…
1. Darker objects absorb & radiate heat faster than lighter objects.

This is why a black asphalt road is hotter than a concrete sidewalk during the day, and why the same road is cooler than the sidewalk after a cold night.

It’s also why a Crookes radiometer spins
The Stefan–Boltzmann law tells us that the power radiated by an object depends on its
A surface area
ε emissivity
T temperature
(σ is a constant)

Emissivity (ε) depends on the color of the object. A perfect black body has ε = 1 & a perfect reflector has ε = 0.
Adding milk/cream 🥛to coffee ☕️ changes the color and alters the emissivity. This slows down radiation of heat.
2. The other factor is viscosity.

More viscous fluids evaporate slower. Evaporation is an important mechanism of cooling (that’s why we sweat btw).

Adding milk/cream to coffee increases viscosity of the coffee and slows evaporative cooling. This makes the coffee cool slower.
If you ever look inside electronic devices you may see another great example of this: heat sinks.

These have a large surface area and are black to optimize radiation of waste heat.
If you like this stuff, I highly recommend reading @ModCuisine.

Great cookbook and blog with fun stuff like this:
modernistcuisine.com/mc/the-physics…

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More from @nickmmark

6 Oct
Yesterday I shared a fun fact that black coffee cools faster than coffee with milk/cream.

Today I woke up early and decided to do an experiment. What followed was interesting & more than a little messy (🤷 that’s science!)

A short 🧵 on ☕️ science
1/
First some background:

Supposedly black coffee ☕️ cools faster for two reasons:
1. Black coffee radiates more heat because black objects have greater emissivity (due to Stefan Boltzmann)
2. Milk 🥛 increases viscosity & decrease evaporative cooling

Should be easy to test?
2/
Methods:
I made coffee & (tried to) warm the 🥛 to the same temperature as the ☕️.

I aliquoted the coffee and combined w/ or w/o 50 ml milk, bringing to the same volume (250ml).

Then I tried to pour both simultaneously into identical cups but managed to make a big mess. 🙊
3/ ImageImageImageImage
Read 7 tweets
5 Oct
When #VaccineMandates for healthcare workers (HCWs) were announced many "experts" warned that there would be a huge exodus of staff in protest.

So far this hasn't happened.

Instead we've just made staff and patients a lot safer.

A short 🧵 of examples
1/
MUSC lost 5 employees out of 17,000 (0.02%)

Indiana University lost 125 workers out of 35,800 (0.3%). Most were part time.

Inova Health lost 89 of 20,000 workers (0.4%).

CristianaCare lost 150 workers out of over 13,400 (that's 1.1%). Most were part time. Just 12 were RNs
2/
Novant Health suspended 375 employees out of 35,000 for non-compliance. 200 got vaccinated. 175 left (0.5%)

New York Presbyterian lost about 250 out of 48,000 employees (0.5%).

UCHealth lost 119 of over 26000 employees (0.4%)
3/
Read 8 tweets
24 Sep
When asked if people should get the flu shot this fall, Paul Marik says “truth be told in the last few years, the risk of being hospitalized after the vaccine was the same as placebo. In recent years the flu vaccine has been completely ineffective...”
1/2 Image
Marik goes on “and indeed I’m not an anti-vaxxer. The risk of Guillian-Barre Syndrome exceeded the risk of being hospitalized … for influenza. So you know what? People need to decide for themselves.”

Yikes! Next these lunatics will be railing against tetanus vaccines.
2/2
For those wondering what Cochrane *actually* says on this subject:

In a population of healthy adults, influenza vaccination reduce influenza & influenza like illness. They may reduce hospitalizations.

For those over 65 yo or with comorbidities the benefits are likely larger. Image
Read 4 tweets
19 Sep
Time for part 4️⃣ of my comparative physiology series:

Case 1
You are called about an elevated blood alcohol level in an inpatient.
"That’s impossible," the tech says, "he’s been admitted to the ICU for a month!"
It’s totally normal, you say, because the sample came from a __
1/
Answer: 🐠
Under anoxic conditions vertebrates produce lactate. This accumulates causing acidosis.
Goldfish & carp are unique b/c they can convert lactate to ethanol, which diffuses out of their gills into the water. They can survive w/o O2 for months!
nature.com/articles/s4159…
2/
Other answers
Bats & primates are good ethanol metabolizers by necessity due to a diet that includes fermented fruit.
The Pen Tailed Shrew is an especially fast ethanol metabolizer: adjusted for size, it consumes the equivalent of 9 beers/day!
3/ URL: https://www.science.org/news/2008/07/now-thats-party-an
Read 24 tweets
15 Sep
One bizarre argument I keep seeing is that “if ivermectin was ‘approved for COVID’ the vaccines would lose their EUA status because there would be an alternative treatment.”

This is untrue (and a particularly stupid argument) for several reasons.

A short thread.
1/ ImageImage
First of all there *ARE* FDA approved, NIH recommended therapies that reduce COVID mortality & are currently in widespread use:
- dexamethasone
- tocalizumab
- baricitinib

If the mere existence of an “alternative therapy” instantly voided an EUA it would have already happened
2/ ImageImage
Second, one of the vaccines (the Pfizer-BioNTech mRNA vaccine) *ALREADY HAS* full FDA approval.

The full approval of the Pfizer vaccine on 8/23 means that Pfizer doesn’t have an EUA anymore. It also didn’t magically invalidate the other 2 vaccine EUAs.
3/
fda.gov/news-events/pr…
Read 8 tweets
4 Sep
The last few weeks have been tough. For those in need of a light hearted thread, here’s a brand new 3rd #tweetorial in my extremes of #physiology series. What can the animal kingdom teach us about our physiology?

Buckle up for some fun animal pulmonary facts 🫁!
1/
CASE 1:
You are performing a bronchoscopy. Upon reaching the main carina instead of the usual TWO airways (right & left mainstem bronchi) you see THREE.

Your assistant says “Whoa! That’s weird”

You say no it’s totally normal because the patient is a:
2/
Answer: 🐖
In pigs, the RUL lobe bronchus originates from the supra-carinal trachea (e.g. before the R & L mainstream branches). The view from the trachea looks like this (see the tracheal bronchus on the right).

image source: casereports.bmj.com/content/12/5/e…
3/
Read 26 tweets

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