about dropping a penny from the top of the Empire State Building?

How if it hits someone on the head it will instantly kill them?

Urban legend!

Totally untrue!

Because of something called “terminal velocity”.

Ill explain in a minute but first I am legally obligated to issue the following warning: Dont rush out to climb to the top of the Empire State Building or any other building - and start tossing stuff off the roof!

A penny might be relatively harmless but anything much bigger definitely could kill someone, and that fact has nothing to do with terminal velocity!

End of warning.

Now lets talk about terminal velocity and what happens when penniesand other things fall from the sky.

On the face of it, it seems plausible that a penny if it got going fast enough could kill you.

Even though its small.

But it turns out falling isnt as straightforward as you thought.

Before cameras and sensors, it was actually pretty hard to study the motion of objects falling through the air.

So Aristotle tried dropping them into fluids, like water, to slow down their motion.

And he found that heavier objects fell faster than lighter ones.

Or, more specifically, objects moved at a constant speed that was proportional to their mass.

But in the late 1500s, Galileo found something different.

He observed objects as they rolled down a ramp and found that the speed of a fall isnt actually constant.

Instead, as the objects rolled down the ramp, they moved faster and faster, accelerating at the same rate, regardless of the mass of the object.

In other words, Aristotle thought objects fell at a constant rate and that a heavy object, like a hammer, would fall faster than a light one, like a feather.

But Galileo thought in the absence of air resistance, they would both fall at the same rate of acceleration.

That was Galileos law of falling bodies.

I just love it when science keeps it simple.

And without knowing it, he was beginning to explain gravity, which accelerates all falling objects at the same rate, forever and ever, (or at least until impact).

On Earth, that rate is about 9.8 meters per second squared.

If we do the math, a penny falling 1250 feet from the Empire State Building at 9.8 meters per second squared should be going almost 200 miles per hour by the time it hits the ground.

Definitely enough to take your eye out, or maybe even kill you.

But thats not what happens because that calculation is incomplete.

See, Aristotle was actually onto something when he dropped things into fluid.

Because here on Earth, falling objects arent just falling.

Theyre falling through the air.

And since liquids and gases are both considered fluids, something thats falling through the air is falling through a fluid.

And thats not the same as falling through nothing.

When objects move through fluids, the objects experience a force called drag.

Think about swiping your hand through water, or walking into the wind.

Drag is a force that opposes motion, pushing back on moving objects and slowing them down.

Part of drag depends on how fast the object is moving higher velocity in one direction equals more drag in the other.

Which means that, at some point, the drag on falling objects gets so high they cant accelerate any more.

And thats kind of a huge dealand super cool.

When the drag force is equal to the gravitational force, the object is falling at its terminal velocity.

Let me say that again.

When drag force equals gravitational force, thats terminal velocity.

That means that no matter how long it falls, in those conditions, it wont go any faster.

So, in the vacuum of space, an object experiencing the pull of gravity from a planet or staror the moon could theoretically accelerate continuously toward that object.

[COMMANDER DAVID SCOTT] “Alright In my left hand, I have a feather.

In my right hand, a hammer.

And Ill drop the two of them here and hopefully, theyll hit the ground at the same time.

How ‘bout that!” [ATHENA BRENSBERGER] It would never reach a terminal velocity.

But within Earths atmosphere, theres only so fast it can possibly fall.

And that top speed depends a lot on what the object is.

The drag force is based on an objects speed, but its also based on its shape specifically, the face of the object thats perpendicular to the direction its moving in.

More surface area on that face equals more drag.

Heres a real-life example.

Back in 2024, an iPhone fell 16,000 feet from a plane midflightand it was completely fine.

If the phone was falling on its edge, its terminal velocity could have been something like 100 miles an hour.

But falling flat, it would have experienced more drag.

And that might have slowed the phone all the way down to around 30 miles an hour by the time it hit the ground.

Or take skydiving.

Human bodies have a terminal velocity around 150 miles an hour, depending on how were positioned.

Generally speaking, thats way too fast to survive.

Which is why a parachute comes in handyit gives you more surface area, and therefore, more drag, so you can slow way down and land safely on the ground.

And going back to the penny.

It would top out at a terminal velocity around 25 miles per hour.

Which would basically just be like a child throwing it at you.

Annoying, but youd probably be fine.

So when you really think about it, falling is pretty complicated.

Maybe it seems like a penny falling from the top of a building could kill a person, but its probably never going to cause much damage.

Still, don't just go throwing things off buildings.