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Some superheros can move[br]faster than the wind.

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The men in Apollo 10 reached

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a record-breaking speed

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of around 25,000 miles per hour

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when the shuttle re-entered

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the Earth's atmosphere in 1969.

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Wouldn't we save a lot of time

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to be able to move that fast?

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But what's the catch?

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Air is not empty.

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Elements like oxygen and nitrogen,

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even countless dust particles,

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make up the air around us.

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When we move past these things in the air,

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we're rubbing against them

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and creating a lot of friction,

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which results in heat.

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Just like rubbing your hands[br]together warms them up

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or rubbing two sticks together makes fire,

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the faster objects rub together,

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the more heat is generated.

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So, if we're running[br]at 25,000 miles per hour,

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the heat from friction[br]would burn our faces off.

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Even if we somehow withstood the heat,

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the sand and dirt in the air

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would still scrape us up

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with millions of tiny cuts

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all happening at the same time.

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Ever seen the front bumper[br]or grill of a truck?

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What do you think all the birds[br]and bugs would do

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to your open eyes or exposed skin?

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Okay, so you'll wear a mask

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to avoid destroying your face.

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But what about people in buildings

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between you and your destination?

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It takes us approximately[br]one-fifth of a second

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to react to what we see.

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By the time we see what is ahead of us

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and react to it -

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time times velocity equals distance

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equals one-fifth of a second

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times 25,000 miles per hour

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equals 1.4 miles

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- we would have gone past it

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or through it by over a mile.

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We're either going to kill ourselves

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by crashing into the nearest[br]wall at super speed

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or, worse, if we're indestructible,

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we've essentially turned[br]our bodies into missiles

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that destroy everything in our path.

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So, long distance travel[br]at 25,000 miles per hour

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would leave us burning up,

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covered in bugs,

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and leaves no time to react.

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What about short bursts

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to a location we can see

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with no obstacles in between?

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Okay, let's say a bullet

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is about to hit a beautiful[br]damsel in distress.

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So, our hero swoops in at super speed,

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grabs her,

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and carries her to safety.

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That sounds very romantic,

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but, in reality, that girl[br]will probably suffer

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more damage from the hero than the bullet

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if he moved her at super speed.

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Newton's First Law of Motion[br]deals with inertia,

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which is the resistance to a change

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in its state of motion.

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So, an object will continue moving

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or staying at the same place

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unless something changes it.

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Acceleration is the rate[br]the velocity changes over time.

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When the girl at rest,

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velocity equals zero miles per hour,

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begins accelerating to reach[br]the speed within seconds,

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velocity increases rapidly

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to 25,000 miles per hour,

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her brain would crash[br]into the side of her skull.

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And, when she stops suddenly,

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velocity decreases rapidly[br]back to zero miles per hour,

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her brain would crash[br]into the other side of her skull,

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turning her brain into mush.

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The brain is too fragile[br]to handle the sudden movement.

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So is every part of her[br]body, for that matter.

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Remember, it's not the speed[br]that causes the damage

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because the astronauts survived Apollo 10,

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it's the acceleration

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or sudden stop

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that causes our internal organs

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to crash into the front of our bodies

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the way we move forward in a bus

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when the driver slams on the brakes.

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What the hero did to the girl

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is mathematically the same[br]as running her over

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with a space shuttle at maximum speed.

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She probably died instantly[br]at the point of impact.

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He's going to owe this poor[br]girl's family an apology

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and a big fat compensation check.

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Oh, and possibly face jail time.

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Doctors have to carry liability insurance

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just in case they make a mistake[br]and hurt their patients.

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I wonder how much superhero[br]insurance policy would cost.

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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.