0:00:14.068,0:00:16.368
If humans could fly,

0:00:16.392,0:00:17.819
without tools and machines,

0:00:17.843,0:00:20.102
how fast do you think we would go?

0:00:20.126,0:00:22.509
As of 2012, the world record

0:00:22.533,0:00:24.606
for fastest short-distance sprint speed

0:00:24.630,0:00:27.339
is roughly 27 miles per hour.

0:00:27.363,0:00:29.236
Running speed depends on how much force

0:00:29.260,0:00:31.114
is exerted by the runner's legs,

0:00:31.138,0:00:34.341
and according to Newton's Second[br]Law of Motion,

0:00:34.365,0:00:38.580
force is the product of mass[br]times acceleration.

0:00:38.604,0:00:40.346
And Newton's Third Law states

0:00:40.370,0:00:41.623
that for every action,

0:00:41.647,0:00:44.759
there is an equal and opposite reaction.

0:00:44.783,0:00:46.744
So, that means running requires

0:00:46.768,0:00:48.546
having a ground to push off from,

0:00:48.570,0:00:52.679
and the ground pushes back[br]against the runner's foot.

0:00:52.703,0:00:55.210
So, flying would actually be

0:00:55.234,0:00:57.390
more similar to swimming.

0:00:57.414,0:01:01.317
Michael Phelps is currently[br]the fastest human in water

0:01:01.341,0:01:04.964
and the most decorated[br]Olympian of all time.

0:01:04.988,0:01:06.690
Guess how fast he swims?

0:01:06.714,0:01:09.359
The answer may surprise you.

0:01:09.383,0:01:11.236
His fastest recorded speed is

0:01:11.260,0:01:15.089
less than 5 miles per hour.

0:01:15.113,0:01:17.368
A child on the ground can easily outrun

0:01:17.392,0:01:18.660
Michael Phelps in water,

0:01:18.684,0:01:20.537
but why is that?

0:01:20.561,0:01:23.224
Well, let's go back[br]to Newton's Third Law of Motion.

0:01:23.248,0:01:24.792
When we run, we move forward

0:01:24.816,0:01:27.087
by pushing against the ground[br]with our feet

0:01:27.111,0:01:28.397
and the ground pushes back,

0:01:28.421,0:01:30.388
propelling us forward.

0:01:30.412,0:01:32.591
The ground is solid.

0:01:32.615,0:01:34.846
By definition, it means the particles

0:01:34.870,0:01:37.181
are essentially locked into place

0:01:37.205,0:01:40.431
and must push back instead[br]of getting out of the way,

0:01:40.455,0:01:43.644
but water is liquid and flows easily.

0:01:43.668,0:01:44.730
When we move our limbs

0:01:44.754,0:01:46.231
to push back against the water,

0:01:46.255,0:01:47.636
a part of the water molecules

0:01:47.660,0:01:49.403
can just slide past one another

0:01:49.427,0:01:50.894
instead of pushing back.

0:01:50.918,0:01:52.528
Now, let's think about flying.

0:01:52.552,0:01:54.448
Air has a lot more free space

0:01:54.472,0:01:56.863
for particles to move past one another,

0:01:56.887,0:01:59.910
so even more of our energy[br]would be wasted.

0:01:59.934,0:02:02.176
We would need to push[br]a lot of air backwards

0:02:02.200,0:02:03.977
in order to move forward.

0:02:04.001,0:02:05.833
Astronauts move around in shuttles

0:02:05.857,0:02:07.905
in zero gravity when[br]they're in outer space

0:02:07.929,0:02:10.915
by pulling on handles installed[br]on the ceiling walls

0:02:10.939,0:02:12.644
and floors of the shuttle.

0:02:12.668,0:02:16.470
Now, imagine you were[br]given the ability to float.

0:02:16.494,0:02:19.263
How would you move[br]around in the middle of the street?

0:02:19.287,0:02:20.764
Well, you wouldn't get very far

0:02:20.788,0:02:23.036
by swimming in air, would you?

0:02:23.060,0:02:24.385
Nah, I don't think so!

0:02:24.409,0:02:26.979
Now, assuming you were[br]granted the ability to float

0:02:27.003,0:02:29.733
and the speed to move around efficiently,

0:02:29.757,0:02:32.600
let's discuss the height of your flight.

0:02:32.624,0:02:34.778
According to the Ideal Gas Law,

0:02:34.802,0:02:36.322
P-V N-R-T,

0:02:36.346,0:02:38.823
pressure and temperature has[br]a positive correlation,

0:02:38.847,0:02:42.203
meaning they increase[br]and decrease together.

0:02:42.227,0:02:44.497
This is because the air expands in volume

0:02:44.521,0:02:45.815
with less pressure,

0:02:45.839,0:02:48.247
so the molecules have more[br]room to wander around

0:02:48.271,0:02:51.920
without colliding into each other[br]and creating heat.

0:02:51.944,0:02:54.087
Since the atmospheric[br]pressure is a lot lower

0:02:54.111,0:02:55.306
in high altitudes,

0:02:55.330,0:02:56.866
it would be freezing cold

0:02:56.890,0:02:58.644
if you were flying above the clouds.

0:02:58.668,0:03:00.097
You'd need to wrap yourself up

0:03:00.121,0:03:01.741
to keep your core body temperature

0:03:01.765,0:03:03.566
above 95 degrees Fahrenheit,

0:03:03.590,0:03:06.436
otherwise you'd start shivering violently,

0:03:06.460,0:03:08.145
gradually becoming mentally confused

0:03:08.169,0:03:09.789
and eventually drop out of the sky

0:03:09.813,0:03:10.925
due to loss of muscle control

0:03:10.949,0:03:13.179
from hypothermia!

0:03:14.272,0:03:16.197
Now, the Ideal Gas Law implies

0:03:16.221,0:03:17.903
that as the pressure decreases,

0:03:17.927,0:03:19.732
gas volume increases.

0:03:19.756,0:03:21.995
So, if you were to fly[br]straight up too quickly,

0:03:22.019,0:03:24.596
the inert gas in your body[br]would rapidly expand

0:03:24.620,0:03:27.433
the way soda fizzes up when shaken.

0:03:27.457,0:03:30.008
The phenomenon is called "the bends,"

0:03:30.032,0:03:31.161
decompression sickness,

0:03:31.185,0:03:32.873
or "divers disease"

0:03:32.897,0:03:35.580
since deep sea scuba[br]divers experience this

0:03:35.604,0:03:37.523
when they come up too quickly.

0:03:37.547,0:03:39.379
This results in pain,

0:03:39.403,0:03:40.379
paralysis,

0:03:40.403,0:03:41.606
or death,

0:03:41.630,0:03:44.641
depending on how foamy your blood becomes.

0:03:44.665,0:03:46.342
Okay, well, let's say you want to fly

0:03:46.366,0:03:47.986
just a few meters above the ground

0:03:48.010,0:03:49.820
where you can still see the road signs

0:03:49.844,0:03:51.306
and breath oxygen with ease.

0:03:51.330,0:03:53.346
You'll still need goggles and a helmet

0:03:53.370,0:03:54.980
to protect you from birds,

0:03:55.004,0:03:55.953
insects,

0:03:55.977,0:03:56.757
street signs,

0:03:56.781,0:03:57.693
electrical wires,

0:03:57.717,0:03:59.550
and other flying humans,

0:03:59.574,0:04:01.150
including flying cops

0:04:01.174,0:04:02.319
ready to hand you a ticket

0:04:02.343,0:04:04.528
if you don't follow[br]the flying rules, buddy.

0:04:04.552,0:04:07.025
Now remember, if you[br]have a collision mid-air

0:04:07.049,0:04:08.941
that knocks you unconscious,

0:04:08.965,0:04:11.050
you would experience free fall

0:04:11.074,0:04:12.933
until you hit the ground.

0:04:14.674,0:04:17.551
Without society or the laws of physics,

0:04:17.575,0:04:20.960
flying would be a totally[br]awesome ability to have.

0:04:20.984,0:04:22.775
But, even if we could[br]all just float around

0:04:22.799,0:04:23.757
a few feet above the ground

0:04:23.781,0:04:25.465
and only moving at a snail's pace,

0:04:25.489,0:04:28.992
I'm telling you, it's still[br]a cool ability that I'd want,

0:04:29.016,0:04:30.738
wouldn't you?

0:04:30.762,0:04:32.892
Yeah, I thought so.

0:04:32.916,0:04:35.392
Now, which superpower physics lesson

0:04:35.416,0:04:37.779
will you explore next?

0:04:37.803,0:04:42.043
Shifting body size and content,

0:04:42.067,0:04:43.401
super speed,

0:04:43.425,0:04:45.024
flight,

0:04:45.048,0:04:47.972
super strength,

0:04:47.996,0:04:50.658
immortality,

0:04:50.682,0:04:52.216
and

0:04:52.240,0:04:54.910
invisibility.