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If humans could fly,

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without tools and machines,

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how fast do you think we would go?

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As of 2012, the world record

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for fastest short-distance sprint speed

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is roughly 27 miles per hour.

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Running speed depends on how much force

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is exerted by the runner's legs,

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and according to Newton's Second
Law of Motion,

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force is the product of mass
times acceleration.

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And Newton's Third Law states

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that for every action,

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there is an equal and opposite reaction.

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So, that means running requires

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having a ground to push off from,

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and the ground pushes back
against the runner's foot.

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So, flying would actually be

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more similar to swimming.

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Michael Phelps is currently
the fastest human in water

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and the most decorated
Olympian of all time.

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Guess how fast he swims?

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The answer may surprise you.

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His fastest recorded speed is

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less than 5 miles per hour.

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A child on the ground can easily outrun

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Michael Phelps in water,

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but why is that?

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Well, let's go back
to Newton's Third Law of Motion.

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When we run, we move forward

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by pushing against the ground
with our feet

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and the ground pushes back,

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propelling us forward.

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The ground is solid.

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By definition, it means the particles

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are essentially locked into place

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and must push back instead
of getting out of the way,

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but water is liquid and flows easily.

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When we move our limbs

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to push back against the water,

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a part of the water molecules

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can just slide past one another

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instead of pushing back.

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Now, let's think about flying.

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Air has a lot more free space

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for particles to move past one another,

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so even more of our energy
would be wasted.

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We would need to push
a lot of air backwards

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in order to move forward.

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Astronauts move around in shuttles

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in zero gravity when
they're in outer space

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by pulling on handles installed
on the ceiling walls

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and floors of the shuttle.

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Now, imagine you were
given the ability to float.

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How would you move
around in the middle of the street?

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Well, you wouldn't get very far

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by swimming in air, would you?

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Nah, I don't think so!

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Now, assuming you were
granted the ability to float

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and the speed to move around efficiently,

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let's discuss the height of your flight.

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According to the Ideal Gas Law,

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P-V N-R-T,

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pressure and temperature has
a positive correlation,

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meaning they increase
and decrease together.

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This is because the air expands in volume

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with less pressure,

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so the molecules have more
room to wander around

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without colliding into each other
and creating heat.

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Since the atmospheric
pressure is a lot lower

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in high altitudes,

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it would be freezing cold

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if you were flying above the clouds.

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You'd need to wrap yourself up

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to keep your core body temperature

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above 95 degrees Fahrenheit,

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otherwise you'd start shivering violently,

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gradually becoming mentally confused

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and eventually drop out of the sky

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due to loss of muscle control

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from hypothermia!

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Now, the Ideal Gas Law implies

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that as the pressure decreases,

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gas volume increases.

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So, if you were to fly
straight up too quickly,

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the inert gas in your body
would rapidly expand

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the way soda fizzes up when shaken.

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The phenomenon is called "the bends,"

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decompression sickness,

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or "divers disease"

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since deep sea scuba
divers experience this

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when they come up too quickly.

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This results in pain,

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paralysis,

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or death,

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depending on how foamy your blood becomes.

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Okay, well, let's say you want to fly

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just a few meters above the ground

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where you can still see the road signs

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and breath oxygen with ease.

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You'll still need goggles and a helmet

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to protect you from birds,

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insects,

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street signs,

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electrical wires,

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and other flying humans,

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including flying cops

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ready to hand you a ticket

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if you don't follow
the flying rules, buddy.

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Now remember, if you
have a collision mid-air

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that knocks you unconscious,

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you would experience free fall

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until you hit the ground.

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Without society or the laws of physics,

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flying would be a totally
awesome ability to have.

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But, even if we could
all just float around

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a few feet above the ground

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and only moving at a snail's pace,

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I'm telling you, it's still
a cool ability that I'd want,

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wouldn't you?

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Yeah, I thought so.

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Now, which superpower physics lesson

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will you explore next?

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Shifting body size and content,

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super speed,

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flight,

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super strength,

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immortality,

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and

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invisibility.