For my 7 year-old Niece

[spiderweb]

She learned today that the earth rotates at about 1,000 mph.

She wanted to know why it was if she jumped up in the air, the earth didn't spin under her at 1,000 mph, and she landed in the same place.

My answer, not being a scientist, was "The Earth loves you, and wouldn't let that happen." (LOL)

What's the real answer?

 

[Clark1961]

That's close enough...


Of course if the Earth is at 1,000 mph so is she.

 

[Bob Noel]

Inertia. She is also going at about 1000 mph. And then gravity pulls her back.

Next time she is in the car going down the highway, ask her to toss a ball or something in the air (don't do the demonstration in a convertible!).

 

[jFlight]

Relative velocity between us standing on the surface and the surface is zero.

 

[Geico266]

The real question is when she hits the ground does she knock the earth off course?

More chance of that happening than man made global warming.

Which begs another question for your niece to ponder......

Wind causes friction and drag. With all of these wind mills going up wouldn't all of that drag (that wasn't there before) cause global slowing?

I need $55'million to study this potentially destructive end to mankind as we know it. Global slowing.... hmmmm. I am surprised algore isn't trying to sell slowing credits.

 

[Mafoo]

The real question is when she hits the ground does she knock the earth off course?

More chance of that happening than man made global warming.

Actually, there is proof without a shadow of a doubt, that man made global warming exists.

The debate, is how much of it is contributing to the warming that's happening naturally.

is it 80%, or .00000000000000000000000000001%. That's the question.

 

[denverpilot]

Kid needs to jump off a merry-go-round looking toward the outside. That'll explain it.

Having a friend or sibling get it up to Warp speed also adds to the fun.

Plus, afterward you can do the water/rope/bucket trick and talk about centrifugal force.

(And then she'll want to know why she's not spun right off the planet.)

Or have they banned such useful physics tools on the modern cushy playgrounds these days? Probably.

Saw some doofuses with a stroller that had tires larger than my first car the other day. Probably had rack and pinion steering and shocks, too. Maybe a Bose MP3 sound system and Bluetooth for the kid's cell phone. Hahaha.

 

[Rigged4Flight]

On a related note, if the plane was on a huge treadmill would it take off? (this question has confounded countless thousands of non-aviation internet geniuses)

 

[Geico266]

Actually, there is proof without a shadow of a doubt, that man made global warming exists.

The debate, is how much of it is contributing to the warming that's happening naturally.

is it 80%, or .00000000000000000000000000001%. That's the question.

I suppose if a man started a camp fire the heat has to go somewhere. just like the little girl jumping and landing on earth. The energy from her jump has to go somewhere and the earth is knocked off it's course.

No comment about global slowing huh? Have to go back and check with the DNC to see if they have a position on the subject?

 

[Geico266]

On a related note, if the plane was on a huge treadmill would it take off? (this question has confounded countless thousands of non-aviation internet geniuses)

It will fly, no problem. You didn't say the treadmill was moving.

 

[Geico266]

She learned today that the earth rotates at about 1,000 mph.

She wanted to know why it was if she jumped up in the air, the earth didn't spin under her at 1,000 mph, and she landed in the same place.

My answer, not being a scientist, was "The Earth loves you, and wouldn't let that happen." (LOL)

What's the real answer?

She is moving as fast as the earth is. If she is in a school bus going down the road and jumps in the isle the bus doesn't speed away. If she jumps out the door when it opens, well that's another story, and the bus driver will have a lot of paper work to do.

 

[AuntPeggy]

The earth loves her.

 

[steingar]

The real question is when she hits the ground does she knock the earth off course?

Of course. She similarly knocked it off course when she took off, via conservation of momentum. The forces she imposed were minuscule, however, and given that her mass is much less than the planet's, did not alter it's course measurably, which is not the same as saying it did not alter it's course at all.

More chance of that happening than man made global warming.

Since it did happen, I suppose MMGW must have as well. Glad you put this stuff everywhere, reminds me of why I don't post in the Spin Zone anymore.

Which begs another question for your niece to ponder......

Wind causes friction and drag. With all of these wind mills going up wouldn't all of that drag (that wasn't there before) cause global slowing?

All those things are really drawing their power from the Coriolis force, which itself is powered by the Earth's rotation. Thus we are slowing down the rotation of the Earth itself. However, the difference in the level of energies involved suggests that we won't slow down the Earth any.

I need $55'million to study this potentially destructive end to mankind as we know it. Global slowing.... hmmmm. I am surprised algore isn't trying to sell slowing credits.

Given that the relative energies are either freely available or simple enough to do on a pocket calculator, I doubt that argument would go terribly far outside your immediate social circle.

Climatology, on the other hand, requires supercomputers and is technically sophisticated and complex enough that the ones who protest the loudest about it are the ones who are least likely to be able to understand it.

 

[tonycondon]

I suppose if a man started a camp fire the heat has to go somewhere. just like the little girl jumping and landing on earth. The energy from her jump has to go somewhere and the earth is knocked off it's course.

No comment about global slowing huh? Have to go back and check with the DNC to see if they have a position on the subject?

i thought there was no such thing as heat.

and i also thought that the earth was slowing down, even without windmills.

 

[rpadula]

The real question is when she hits the ground does she knock the earth off course?

http://what-if.xkcd.com/8/

 

[MAKG1]

i thought there was no such thing as heat.

and i also thought that the earth was slowing down, even without windmills.

It is. Those pesky tides. It's also making the moon get further away, trading orbital binding energy and rotation energy for a little bit of heat and a lot of reconfiguration of coastlines.

Windmills don't take their energy from the coriolis force. No windmill is nearly large enough for that to be significant. And coriolis force is always at right angles to velocity, which means it doesn't change the energy (it can, however, shape the direction). Winds are generated by temperature differences, both local and global scale. The temperature differences all come from the sun in one way or another; if there were no sun, there would be no winds.

So, wind energy is a heavily processed solar energy. So is anything else aside from nuclear.

For the 7 year old, the merry-go-round experiments (both on it and watching from outside) are extremely valuable. Two specific things to try are (1) holding a ball and just letting it go (on the MGR, it's obvious centrifugal force; off, it just goes in a straight line on a tanget), and (2) playing catch (onboard, it's a vivid demonstration of coriolis force; off, it just makes the usual parabolic arc). She sounds like a bright kid. Have fun with this.

The University of Oregon used to have a lot of kid-oriented animations (like cow bombing, etc.) to explain these sorts of things. I wonder if those are still around.

 

[dukeblue219]

It will fly, no problem. You didn't say the treadmill was moving.

It'll fly regardless of how fast the treadmill is moving. A plane doesn't deliver power through its wheels, so the prop will still accelerate the plane to a normal airspeed, even if that means that wheels are spinning across the treadmill at 500mph because the treadmill is going warp speed backwards.

 

[MAKG1]

It'll fly regardless of how fast the treadmill is moving. A plane doesn't deliver power through its wheels, so the prop will still accelerate the plane to a normal airspeed, even if that means that wheels are spinning across the treadmill at 500mph because the treadmill is going warp speed backwards.

The Mythbusters tried this out. With a real pilot, STOL aircraft, and a homemade massive "treadmill." The real pilot got the wrong answer!

 

[denverpilot]

Climatology, on the other hand, requires supercomputers and is technically sophisticated and complex enough that the ones who protest the loudest about it are the ones who are least likely to be able to understand it.

And supercomputers use too much energy and threaten the climate. ROFL!

 

[Clark1961]

i thought there was no such thing as heat.

This is true since warm weather is merely the absence of cold weather, e.g. what folks perceive as heat is actually the absence of cold.

 

[MAKG1]

This is true since warm weather is merely the absence of cold weather, e.g. what folks perceive as heat is actually the absence of cold.

Gravity doesn't exist. The earth sucks.

 

[DaytonaLynn]

The real question is when she hits the ground does she knock the earth off course?

More chance of that happening than man made global warming.

Which begs another question for your niece to ponder......

Wind causes friction and drag. With all of these wind mills going up wouldn't all of that drag (that wasn't there before) cause global slowing?

I need $55'million to study this potentially destructive end to mankind as we know it. Global slowing.... hmmmm. I am surprised algore isn't trying to sell slowing credits.

I said this theory to an environmentalist and they got so mad I cannot print the things they said to me. Makes as much sense to me as their argument.

 

[bflynn]

Argh, he started a treadmill thread!

Yes, it flies. Yes, for a fraction of a second, a theorethical treadmill accelerating at impossible speeds could keep an airplane from moving forward, because there IS a small backward acceleration force transferred to the axle. No, no treadmill like that actually exists, so the answer is that it flies. As seen on TV.

We can now have 300 pages of thread discussing the answer.

 

[MAKG1]

I said this theory to an environmentalist and they got so mad I cannot print the things they said to me. Makes as much sense to me as their argument.

That's because you built straw men on straw men.

The argument is one of those Feynman described as "not even wrong." When the starting point has no relation to reality, there is no coherent argument that the target won't misinterpret.

That's not a theory. That's a wild guess. There is a large difference.

 

[MadseasoN]

Argh, he started a treadmill thread!

Yes, it flies. Yes, for a fraction of a second, a theorethical treadmill accelerating at impossible speeds could keep an airplane from moving forward, because there IS a small backward acceleration force transferred to the axle. No, no treadmill like that actually exists, so the answer is that it flies. As seen on TV.

We can now have 300 pages of thread discussing the answer.

It already happened about 4-5 months ago.

Back to topic - velocity is relative. The Earth is turning at ~1Kmph (at the Equator) but not in relation to anything on it. Next time she's riding in the car ask her to throw a tennis ball up. It's moving at the same speed as she is, so it falls back in the same place.

 

[PPC1052]

it's obvious centrifugal force; off, it just goes in a straight line on a tanget

In one of his more pedantic moments, my physics teacher went to great pains to drill into our heads that there is no such thing as centrifugal force.

Centripetal force? Yes. Inertia? Yes. Centrifugal force? No.

 

[MAKG1]

In one of his more pedantic moments, my physics teacher went to great pains to drill into our heads that there is no such thing as centrifugal force.

Centripetal force? Yes. Inertia? Yes. Centrifugal force? No.

I hope he didn't word it unqualified like that. It's wrong as stated.

In an inertial frame of reference, there is no centrifugal force. There is a centripetal force instead, if there is a rotating object (that makes it do other than fly in a straight line). In a rotating frame of reference like on a merry go round, there is a very real centrifugal force.

It's much easier to work in an inertial frame, so intro classes are often taught that way, exclusively. And centrifugal force is very often a source of massive confusion in Physics 101, hence the focus.

 

[PuertoRicoFlyer]

It'll fly regardless of how fast the treadmill is moving. A plane doesn't deliver power through its wheels, so the prop will still accelerate the plane to a normal airspeed, even if that means that wheels are spinning across the treadmill at 500mph because the treadmill is going warp speed backwards.

No. An airplane flies due to relative wind over the wing regardless of what is happening across the ground. If the treadmill is going backwards at the same speed the airplane is "trying" to move forward the relative wind speed is 0 and it goes nowhere. But if the airplane moves forward faster than the treadmil is going backwards then the relative wind over the wing may be enough to get it airborne.

Just like taking off with a tailwind, flying a glider or lifting off in a helicopter. B)

 

[ja_user]

Ok. So engage the parking brake on the plane, and then run the treadmill backwards....

That's right, throw it into the wind

 

[PuertoRicoFlyer]

The Mythbusters tried this out. With a real pilot, STOL aircraft, and a homemade massive "treadmill." The real pilot got the wrong answer!

But the airplane in that episode reached a faster speed forward than the treadmill's was going backwards so the relative wind became enough for it to fly. If that treadmill would have been at 50mph that airplane would not have gone anywhere. The ultra-light pilot in that episode didn't understand aerodynamics of flight. B)

 

[PuertoRicoFlyer]

Ok. So engage the parking brake on the plane, and then run the treadmill backwards....

That's right, throw it into the wind

How do you think airplanes take off from aircraft carriers? They get thrown into the wind. B)

 

[spiderweb]

On a related note, if the plane was on a huge treadmill would it take off? (this question has confounded countless thousands of non-aviation internet geniuses)

Yes, it would.

 

[spiderweb]

She is moving as fast as the earth is. If she is in a school bus going down the road and jumps in the isle the bus doesn't speed away. If she jumps out the door when it opens, well that's another story, and the bus driver will have a lot of paper work to do.

Haha. Good illustration.

Now, if she could jump 100 miles above the earth, I assume that with the time that would take, and the time to come back down, the earth would start to rotate under her.

 

[spiderweb]

The earth loves her.

Haha, I tried that one already!

 

[silver-eagle]

How do you think airplanes take off from aircraft carriers? They get thrown into the wind. B)

They didn't used to. It was the catapult that changed that.
So if I drive in an easterly direction as fast as my car can go and a cop pulls me over and writes a ticket for doing 120 I get to challenge him in court because I was actually doing 1,120mph.
Great! Liar Liar.

 

[spiderweb]

They didn't used to. It was the catapult that changed that.
So if I drive in an easterly direction as fast as my car can go and a cop pulls me over and writes a ticket for doing 120 I get to challenge him in court because I was actually doing 1,120mph.
Great! Liar Liar.

LOVE this!

 

[MAKG1]

No. An airplane flies due to relative wind over the wing regardless of what is happening across the ground. If the treadmill is going backwards at the same speed the airplane is "trying" to move forward the relative wind speed is 0 and it goes nowhere. But if the airplane moves forward faster than the treadmil is going backwards then the relative wind over the wing may be enough to get it airborne.

Just like taking off with a tailwind, flying a glider or lifting off in a helicopter. B)

Watch that Mythbusters episode again. It's on Netflix.

The treadmill is irrelevant. Acceleration takes place because of the propeller and the air, and it is not possible to wind off that treadmill as fast as the aircraft "wants" to go. No matter how fast you try, it "wants" to go faster.

It is not at all like taking off with a tailwind unless you think tires provide propulsion.

 

[denverpilot]

So if I drive in an easterly direction as fast as my car can go and a cop pulls me over and writes a ticket for doing 120 I get to challenge him in court because I was actually doing 1,120mph.
Great! Liar Liar.

You forgot the amount of distance the Earth as a whole covered during your drive East, and expansion of the Universe.

You were going a lot faster than 1120.

 

[denverpilot]

P.S. The answer for the little girl is, "Because the Flying Spaghetti Monster says so."

 

[Rigged4Flight]

PoA: Where an innocent child's question can turn in to a debate over global warming.

My $0.02: The earth has been warming ever since the height of the latest ice age. I have no doubt that factories and deforestation have contributed to it, much like the flutter of butterfly wings contributes to wind patterns, but I'm fairly certain that global warming was not caused by humans. Unless those pesky people that lived thousands of years ago were up to a lot more mischief than we give them credit for.

And on a lighthearted note, I'll just leave this right here.