Question

The source of the Mississippi River is closer to the center of the Earth than is its outlet in Louisiana (because the Earth is fatter at the equator than at the poles). Explain how the Mississippi can flow "uphill."

Answer 1

@agent0smith can you help me with this question please, I have been stuck on it for days

Answer 2

http://message.snopes.com/showthread.php?t=5457

Answer 3

its a myth

Answer 4

That doesn't make sense. The gravitational force is stronger the closer the water is to the centre of earth, so it shouldn't flow from a high gravitational region to a lower one. Unless there's some other forces acting, which might require geological knowledge vs physics.

Answer 5

no river on earth flows uphill unless something of monumental proportions happens like an earthquake. I read something about the 1812 madrid earthquake changing its course temporarily, but im going with this being impossible.

Answer 6

So far I understood that the source is closer because it closer to the CM of the axis but how would I apply all this to the question.. I cant relate to it

Answer 7

Do you know if your professor was looking for you to explain why its not possible?

Answer 8

I am not sure, that is not in the question though..

Answer 9

does this have to do with north and south, Miss River is closer to north so its closer to the CM, if we move down south is further away from CM?

Answer 10

http://answers.yahoo.com/question/index?qid=20071118185625AAKWR2N

Answer 11

Notice "uphill" is in " "

Answer 12

what does the uphill mean in this case

Answer 13

bah, trick question

Answer 14

Uphill means flowing from south to north in this case it seems.

Answer 15

see if what I said was true before then the water can go uphill because the force is greater since the distance is smaller between the two

Answer 16

between river and CM

Answer 17

Idk. I don't know which way the river flows and the question doesn't help find out.

Answer 18

yes exactly, I am not sure what they mean by uphill because its in " "

Answer 19

pretty sure our professor want us to fail ahaha

Answer 20

If you read the answers in that link i gave above, it should have what you need. Stupid question imo (seems like you need to know something about what way the Mississippi runs), way too confusing and the " " don't help.

Answer 21

i know I wanted to ask the prof but he wasnt in his office, as usual =I

Answer 22

http://gsjournal.net/Science-Journals/Essays-Geophysics/Download/4786

Answer 23

^wow, they used "centrifugal force" like five times on the first page :/

Answer 24

But it sounds like it's more due to the rotation of Earth, than gravity - the water's inertia, due to rotation, carries it uphill is my guess. But any explanation where "centrifugal force" is used repeatedly doesn't help understand why it happens.

Answer 25

ahaha nvm I will not be using that source, that kind of makes sense

Answer 26

I might just put what you said and I said altogether and submit it, this question is crazy

Answer 27

Thank you very much @agent0smith and @skay

Answer 28

how does this sound for a guess, Miss River is closer to north so its closer to the center of the Earth, if we move down to the south it is further away from center of the Earth,The water can go uphill because the force is greater since the distance is smaller between the Mississippi River and the center of the Earth.

Answer 29

^i think it's due more to the rotation of earth tho, but idk. If the chapter was on circular motion i'd go with something about it

Answer 30

it was on centripetal force

Answer 31

oh... there you go then. the waters inertia due to rotation prob makes it flow uphill.

Answer 32

is that all for it, I dont know if I should add more.

Answer 33

in class we did talk about mass, gravity and forces about the a circle and an object but I am not sure if that would apply in this case?

Answer 34

it is ch.5 if you want to take a look at in the 6th edition

Answer 35

well i have the 6th edition giancoli but idk if it'd help. I don't have a teacher's edition of the book for some reason.

Answer 36

oh thats fine, I might just put down what you said and then ask him about it bc it due tomorrow,

Answer 37

thank you for helping me

Answer 38

The Mississippi is flowing away from the centre of the Earth, because weight is the result of gravity and inertial forces (namely centrifugal force here).

It is NOT flowing uphill though, because vertical is defined parallel to weight and does not coincide with the Earth's radius.

This is the same reason for which Cimborazo's summit in Ecuador, although furthest away from Earth's centre, is only 6,268 m , whereas Everest, closer to Earth's centre is 8,848 m.

Answer 39

To complete my post, if Earth's rotation stopped, then the Mississippi would reverse its flow and Chimborazo would be the highest point above sea level.

Answer 40

@Vincent-Lyon.Fr what "centrifugal force" ...? And how is weight related to inertia? Weight is due to gravity.

Answer 41

An object in zero gravity has no weight, but still has inertia due to its mass.

Answer 42

"To complete my post, if Earth's rotation stopped, then the Mississippi would reverse its flow" - this seems to says it IS flowing uphill - it's flowing from a region of higher gravitational pull, to lower gravitational pull, which is due to Earth's rotation and the water's inertia keeping it moving in that direction.

Answer 43

The term 'zero gravity' is misleading.

When astronauts are floating in the ISS, they are experiencing the gravitational force of Earth. The gravity there is just a few percent less than at Earth's surface.
But their weight relative to the ISS is zero. Thus is should be call 'zero-weight', not 'zero gravity'.

Weight (in a certain frame) is the vector sum of gravitation and inertial forces in that frame.

For the astronaut, weight points toward the Earth and the inertial force is the exact opposite, hence zero-weight.

Answer 44

If the Earth stopped rotating, the vertical line at any point on Earth except the Poles and on the Equator would shift. And the Mississippi would change its direction of flow.

In any case, it is always flowing downhill (i.e. down relative to the local vertical).

Answer 45

by zero gravity - i meant literal zero gravity, not astronauts in a gravitational field.

inertial forces - you're going to have to explain this. Objects have inertia, they do not have inertial force. What would provide this inertial force?

Answer 46

There is no outward force on an astronaut in orbit around Earth - there is their tangential velocity, which is perpendicular to the force of gravity (they're not weightless even though they may feel they are)

Answer 47

Q: "What would provide this inertial force?"
A: an accelerated frame of reference

Inertial forces are pseudo-forces that mathematically take into account the effects of being in an accelerated frame of reference.
If your car brakes, you tend to keep your motion because of inertia. From within the car's frame of reference, you have to add an artificial force \(\vec F_i = -m\;\vec a _{car}\) pointing forward since \(\vec a_{car}\) is pointing backwards. (m is the mass of the body)

The so-called centrifugal 'force' is one of those \(\vec F_i = +m\;\omega^2 \;r \;\hat r\)
where \(\omega\) is Earth rotation velocity, r the distance of the body to the axis and \(\hat r\) the unit vector pointing away from the axis.

Answer 48

Your definition of weight coincides with gravity. This is true only in inertial (or Galilean) frames of reference. If you are dealing with moving frames of reference, you need to distinguish weight from gravity.

The satellite, once in orbit, is an extreme example where weight happens to be exactly zero.

The rotating Earth is not a Galilean frame of reference. So anytime you are writing 'net force = 0' for an body in equilibrium, you need to take into account the extra centrifugal force. The Mississippi is always going downhill relative to the local vertical (see figure), not relative to the Earth's radius. That's where the paradox lies (and that's why the word 'uphill' was written within quotes in the initial question).

Answer 49

"If your car brakes, you tend to keep your motion because of inertia. From within the car's frame of reference, you have to add an artificial force F⃗ i=−ma⃗ car pointing forward since a⃗ car is pointing backwards. (m is the mass of the body)"

I used to think this too (and solved a few problems using it, it works fine) - but it's not necessary. There's no need for an artificial force in an accelerating frame of reference - list all real forces, and take into account that there's an overall net force on the frame of reference (which is a real force, just provided externally, by the car tires/friction with the road).

SOMETHING provides the force. In the case of the car, your seatbelt will provide the force to slow you down - the net force on your body (in the horizontal direction) is due to the tension in the seatbelt, hence you decelerate. There is no inertial force, but there is a reaction force of you pushing on the seatbelt, due to the seatbelt applying a force on you to decelerate you - but i wouldn't call this an inertial force, only a reaction force, as it would not exist w/o the seatbelt.

The reason the astronauts *feel* weightless is due to the fact that they're essentially in freefall around Earth, just like you feel weightless when falling - you only "feel" your weight if there's a reaction force (like the ground under your feet) to remind you of your weight.

I understand what you're saying about Earth's rotation having an effect, I just disagree with some of it... The net force on an astronaut is not zero - if it were, how would they continue to orbit? If the net force on them were zero, then there is no acceleration to stop them from continuing to travel on a path tangent to the curvature of Earth. An object in orbit needs a net force towards the body it's orbiting.