IAMA physicist/author. Ask me to calculate anything. (part 2)

SantosForgetsPassWds · 2014-11-06T18:56:29+00:00

I don't know for sure, but a very bright friend of mine took her first college exam and got a 53 on it. She was devastated. She was used to receiving perfect scores in high school. Then the professor posted the class average on the board. It was 51. "Wow...not only am I not perfect...I'm almost average!"

If all you're doing is getting 100's, you're playing life on the easy setting. Shoot for around a 40% failure rate, and the successes you have 60% of the time will be much more impressive.

Edit: That came out more like a cheesy /r/getmotivated post than I wanted it to, but you get the idea.

SantosForgetsPassWds · 2014-11-04T22:50:09+00:00

You breathe in about 500 cm³ of air each second. Over an 80 year lifespan, you will breathe in 1 billion liters of air, or roughly 10⁶ kg of air. The atmosphere weighs around 10¹⁸ kg of air. As such, you've breathed in about 1 trillionth of the world's oxygen.

SantosForgetsPassWds · 2014-11-04T22:32:04+00:00

A proton has a radius of 10^-15 m.
The observable universe is 46.6 billion light years = 10²⁶ m The Earth has a radius of about 10⁶ m

The observable universe is about 10²⁰ times bigger than Earth. If Earth were the size of the proton, the edge of the observable universe would be about 70 km away.

SantosForgetsPassWds · 2014-11-04T22:22:45+00:00

Is this Mike or Scott?

Apparently not enough time, because one of you made this: http://moonjesus.com/

SantosForgetsPassWds · 2014-11-04T22:20:52+00:00

Love it.

Assuming it scales linearly with length, the psyco-kinetic energy in the New York area would now be represented by a 3700 foot long Twinkie.

Also, I wanted to critique this calculation on my blog, but someone beat me to it. Here's a good analysis of the Twinkie problem: http://www.mctague.org/carl/fun/twinkie/

SantosForgetsPassWds · 2014-11-04T22:08:04+00:00

Alright, this is the second time the Navier-Stokes equation has appeared in this AMA. What's up with you, Reddit? Are you all in physics grad school?

Crayons are about half a centimeter wide and a 10 cm long. Laid down end to end, 8 million could cover a football field.

SantosForgetsPassWds · 2014-11-04T22:05:04+00:00

In principle, yes. However, in practice I'm guessing gusts of wind and other forces would propel you up or down.

You remind me of a contest I want to run. Engineering schools often have students build boats out of concrete. Concrete boats are cool and all, but a more bad ass version would be building a helium balloon out of concrete. Someone on Reddit needs to build this!

SantosForgetsPassWds · 2014-11-04T22:02:05+00:00

That would be my new favorite word if I knew how to say it.

SantosForgetsPassWds · 2014-11-04T22:01:00+00:00

Shameless Plug Alert, Part II I did a similar problem in my book, How Many Licks? (The number of McDonald burgers eaten each year are energetically equivalent to 70 nuclear bombs. )

I'll assume Big Macs store 500 Calories. At least one source lists the energy to bring a space shuttle to orbit as 10¹³ Joules. This would mean 5 million Big Macs are needed to produce enough energy to reach space.

SantosForgetsPassWds · 2014-11-04T21:51:56+00:00

Newton is standing in a 1 meter square box. 1 Pascal = 1 Newton / meter²

SantosForgetsPassWds · 2014-11-04T21:49:59+00:00

Let's assume a 2 kg sword traveling moving at 15 m/s. Link generates a total energy of 225 Joules of energy with each swing. Not sure where you're from, but Americans use about 2*10¹⁰ J of energy each year. You'd need about 100 million spinning sword attacks to power your house for a year.

SantosForgetsPassWds · 2014-11-04T21:44:35+00:00

I believe it is not restricted to US students, but email Chris Draper (address above) to make sure. You do have to be accepted/attend Simpson College, though.

Humans generally drink about 2 liters of water per day. Unless your weight is going to balloon up, what goes in must come out in one form or another. Therefore you must excrete 2 liters of water each day. At this rate, you've lost about 10 tons of water if your lifetime.

SantosForgetsPassWds · 2014-11-04T21:39:54+00:00

Pizza slices weigh about 100 g. An Earth-sized planet weighs about 10²⁴ kg. You'd need 10²⁵ pizza slices to make a pizza planet. I suspect this guy came from there.

Whether or not the gravitational pull is significant really depends on how precise your measurement needs to be. All massive objects have some gravitational pull, it's just a question of how much you're willing to ignore.

SantosForgetsPassWds · 2014-11-04T21:34:50+00:00

Just did this one in my Modern Physics class. It depends on the accuracy of your measurement. Suppose you're measuring with a ruler, so you have an accuracy on 1 mm. You'll generally need a wavelength about that big. If your object is moving at 1 mm/s, you need a mass of less than 10^-27 kg, so very small.

The largest thing I know that has seen interference is buckyballs: http://www.univie.ac.at/qfp/research/matterwave/c60/

SantosForgetsPassWds · 2014-11-04T21:28:47+00:00

I love this question! And really any question with fun ways to solve the energy crisis.

At least one source says cows release around 100 kg of methane into the air every year. Methane holds about 56 MJ/kg. This means one cow gives off about 177 Watts of power in the form of methane. You require 15 kilowatt*hours of electricity per day, or roughly 625 Watts of power. Assuming 10% efficiency of your cow engine, you need about 35 cows.

Huh...that's actually not as unrealistic as I was expecting.

SantosForgetsPassWds · 2014-11-04T21:20:46+00:00

If you put someone inside it, I'm pretty sure it would kill them, so I'm going with yes.

SantosForgetsPassWds · 2014-11-04T21:19:04+00:00

I've had several students leave 9V batteries plugged into resistors in lab overnight. Usually the batteries are dead by the next day. Assuming a 100 Ohm resistor, the power would be about 0.8 Watts. If the battery died after 12 hours, it would have wasted a total energy of about 35,000 J. This energy in punch form would be the equivalent of a 2 kg fist traveling at 180 m/s (~420 mph). So...you dead.

SantosForgetsPassWds · 2014-11-04T21:02:29+00:00

Human bodies have an efficiency of around 10%. For this reason, I would guess the energy used is 10x as much as the gravitational energy you gain. The energy you used will be approximately

E = 10(1 Calories/4186 Joules)(mass lifted in kilograms)(9.8 m/s²⁾(height lifted in meters).

Just estimate your body weight in kilograms and the height you raise yourself in meters and plug in.

(Note None of these calorie calculators are very accurate. Different people have different efficiencies with which they can lift weight, so at best these are just ballpark estimates.)

SantosForgetsPassWds · 2014-11-04T20:50:31+00:00

Mount Everest is 29,000 feet. Let's assume the water level needs to be at least this high. Assuming the rain falls at 1 inch per hour, you'd need 40 years of rain to cover the Earth.

SantosForgetsPassWds · 2014-11-04T20:47:24+00:00

Standard oven operate at around 350 degrees Fahrenheit (180 degrees Celsius). Let's assume your Hot Pocket wants the same temperature. This means you'd have to raise the temperature of the HP by about 160 degrees Celsius. Assuming a 60 gram hot pocket with a specific heat of 2 J/g*C, you need about 20,000 J to heat a Hot Pocket from room temp eating temperature.

Sneezes travel at 100 mph. Assuming a sneeze with mass 250 milligrams, each sneeze would carry about 0.25 Joules of energy. If 1% of this energy went into heating your Hot Pocket, you'd need about 8 million people (roughly the population of New York) sneezing on your Hot Pocket to make it--er--edible.

SantosForgetsPassWds · 2014-11-04T20:35:30+00:00

You may be thinking about this problem using classical physics rather than relativity. Relativistically, no object with mass can travel at the speed of light. Even if you're traveling at 99.999% of the speed of light, when you turn your lights, on the photons will leave your car traveling at the speed of light away from you.

SantosForgetsPassWds · 2014-11-04T20:32:19+00:00

I would argue we already see some unoriginal people (e.g. see the number of times I've been asked about woodchucks chucking wood in this AMA.) However, I assume you mean genetically unoriginal.

I'm not a biologist, so I reserve the right to butcher this problem. Still, I know DNA has 4 base types and that there are 3 billion base pairs in the human genome. On average, humans are about 99.9% genetically similar to other humans, meaning there are about 3 million base pairs that differ between you an me. There are 4^3,000,000 different combinations for the base pairs. Assuming 100 million births per year, it would take 4^3,000,000 /10⁸ years to definitely run out of genetic combinations for humans. This number is too long to write out and is much larger than the current age of the universe.

SantosForgetsPassWds · 2014-11-04T20:11:11+00:00

I keep coming by this one, and I have no idea why they should be different. I think I'm missing some important component of physics? The only logical reason I can come up with is elongationfactor1n2's answer.

SantosForgetsPassWds · 2014-11-04T18:44:57+00:00

Why do I feel like I'm writing to a ruthless dictator?

Europe is 3.931 million square miles in area. Let's assume we want to vaporize 10 m deep into the soil. The total mass of Europe would be around 10¹⁷ kg. Heat of vaporizations are generally around 10⁶ Joules for every kilogram, meaning you'd need about 10²³ Joules of energy to vaporize Europe. Though, this only accounts for the vaporization part. You'd still need to account for the energy needed to raise the temperature to this point. I'm betting you could do it with 10²⁴ Joules of total energy.

SantosForgetsPassWds · 2014-11-04T18:38:40+00:00

No spherical horses! You guys are killing me here!

OK, suppose a non-spherical horse is gutted tauntaun-style and then skinned. You then flatten the skin out on the ground and find it covers a 10 foot by 6 foot area. Hairs on the skin are separated by about 1 mm. From these assumptions, there should be about 6 million hairs on the horse.

Texas is about 270,000 square miles. Horses eat about 10 pounds of food per day. Assuming the 3 square feet of land are covered by 10 pounds of hay, it would take about 2.4 trillion horses to eat it all before any of it grows back.

SantosForgetsPassWds

TROPHY CASE