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Holding a cup of water in a giant drop.

MustangSVT

MustangSVT

Lifer
Ok, I just watched this clip on youtube.
http://youtube.com/watch?v=wyfSA2oQQgg

It is a test done to see what happens to a cup of water when it fell with a rider in a giant drop(a free fall amusement ride).

About 1/3 of the water floats out during initial fall.

And they explain it saying...

"the Giant drop falls faster due to heavier weight"

errrr.. If that's true.. then they are rewriting newton's 2nd law.

but then the water clearly floats out.

what other forces are at work ?

The ride is a free fall , thus it will have same pull from earth..
hmm, is it the air pressure? is it the bounce in the guy's arms?

wake my old brain up please 😀
 
it's going to fall exactly the same speed as the riders, but the slightest jostle will give water upwards momentum since it's in a open-topped container, and since it's in a free fall like the rider, the upwards momentum is very noticeable, ie - the water floats up.

edit: to clarify - if they were able to hold the cup of water perfectly still, it wouldn't do that.
 
Think about spraying a water spray bottle. The small droplets flow down very slowly. Now think about water vapor suspended in the air. It isn't the actual weight of the water drops, it is the surface area vs weight.
 
yeah, especially in the replay you can see it only starts coming up after it sloshes up against the cup.
 
Originally posted by: Safeway
Think about spraying a water spray bottle. The small droplets flow down very slowly. Now think about water vapor suspended in the air. It isn't the actual weight of the water drops, it is the surface area vs weight.
Click to expand...

That doesnt apply here.

that happens because there is air resistance, but this one starts from a cup.

Yeah, like Auggie said, only thing I could think of was that guys arm moving. hmm
 
Originally posted by: Auggie
it's going to fall exactly the same speed as the riders, but the slightest jostle will give water upwards momentum since it's in a open-topped container, and since it's in a free fall like the rider, the upwards momentum is very noticeable, ie - the water floats up.

edit: to clarify - if they were able to hold the cup of water perfectly still, it wouldn't do that.
Click to expand...

can you explain why, in a similar situation (Demon Drop at Cedar Point), a coin placed on your knee, will 'float' above your knee as you drop?

hmm, as I was typing this, i figured it out.

the water will do that every time. Why? Because the cup actually should be falling at the same rate the water is, but the water isn't being contained, but the cup is (by being held). The body holding the cup? The body would also fall at the same rate as the water (thus, appear to float as compared to the vehicle the body is in as it falls at a slightly different rate). But the body is being held onto, by seatbelts and restraints.

think of it this way: you kind of float out of your seat when a ride or rollercoaster train plummets. Technically you should fall at the same rate, right? but for some reason on a drop, if we weren't restrained, we would 'float' right out of our seats. Theoretically, we should fall at the same rate as the vehicle we are in, but I'm not so inclined to believe that. The car might very well reach the ground proportionally faster than we do.. ie, the distance between the vehicle and our body would continue to grow, thus the vehicle has to be traveling faster than our body.
Right?
 
Terminal velocity of the ride is greater than that of the water in the cup, which is not secured to the ride like cup is.
 
Originally posted by: nonameo
Terminal velocity of the ride is greater than that of the water in the cup, which is not secured to the ride like cup is.
Click to expand...

but terminal velocity just requires a greater drop distance to reach... everything is supposed to fall at the same exact rate of acceleration, correct? Air resistance being the only thing that would prevent that from occurring?
 
I didnt think of that, but that's very true, the ride starts you off w/ some velocity, probabley a little less then gravity so the water at a standstill has to catch up.
 
Well, now I'm second guessing that idea, because the water outside the cup falls at the same rate as the rest of the ride. Perhaps it is just getting pushed out by air currents?
 
Inertia.

An object at rest wants to stay at rest. When the drop drops, the water isn't contained by a lid so it wants to stay still for a split second until gravity gets it moving after the cup starts to go down.

But Youtube is blocked at work so I can't actually see the video.

 
If it's at absolute free fall then the water should stay in the cup, but if the ride pushes the riders down even just briefly, then the water should move out of the cup. Even in free fall though, a slight jostle of the cup will cause the water to slosh out and if it then hits the air rushing by, it will be forced further up relative to the cup. The rider and the seat and the cup will fall faster than the water drops due to a greater ratio of mass to surface area. At least that's what I think. 😉
 
Even astronauts can't hold a cup of water without it spilling everywhere. As mentioned any movement at all of the cup will cause the water to spill out.
 
Originally posted by: Kelemvor
Inertia.

An object at rest wants to stay at rest. When the drop drops, the water isn't contained by a lid so it wants to stay still for a split second until gravity gets it moving after the cup starts to go down.

But Youtube is blocked at work so I can't actually see the video.
Click to expand...

GASP!!! for a split second it defies gravity?! GASP!!!!

sigh.. :roll:
 
Originally posted by: Safeway
Think about spraying a water spray bottle. The small droplets flow down very slowly. Now think about water vapor suspended in the air. It isn't the actual weight of the water drops, it is the surface area vs weight.
Click to expand...

That's a really bad example. The droplets from a sprayer stay up due to the air resistance. The water in the cup didn't come out due to that.
 
Originally posted by: nonameo
Terminal velocity of the ride is greater than that of the water in the cup, which is not secured to the ride like cup is.
Click to expand...

Wrong.

This came out right at the beginning, so terminal velocity didn't come into play.
 
A few things factor in: Surface tension, wind resistance, and attraction of the water to the container by its wetting action.

My take: The water will try to hold itself in the cup by way of surface tension, as well as its attraction to the cup. (Water has a polar molecular structure, which gives it its "wetting" action.)
But outside, there's turbulent air. Air in motion has lower pressure than air that's not moving. This low pressure could serve to allow the water to try to push its way out of the container.
Turbulent flow would also be a factor - pressure on one part of the surface of the water will be different from that on another. Uneven pressure like that can cause movement.
Then the plane takes off.
 
The inertia of the water and the coin cause them to rise up, imo.

They tend to remain still, and they are not connected to the ride, so their inertia makes them stay still until gravity overcomes their inertia and they begin to free fall.
 
Originally posted by: destrekor
Originally posted by: Auggie
it's going to fall exactly the same speed as the riders, but the slightest jostle will give water upwards momentum since it's in a open-topped container, and since it's in a free fall like the rider, the upwards momentum is very noticeable, ie - the water floats up.

edit: to clarify - if they were able to hold the cup of water perfectly still, it wouldn't do that.
Click to expand...

can you explain why, in a similar situation (Demon Drop at Cedar Point), a coin placed on your knee, will 'float' above your knee as you drop?

hmm, as I was typing this, i figured it out.

the water will do that every time. Why? Because the cup actually should be falling at the same rate the water is, but the water isn't being contained, but the cup is (by being held). The body holding the cup? The body would also fall at the same rate as the water (thus, appear to float as compared to the vehicle the body is in as it falls at a slightly different rate). But the body is being held onto, by seatbelts and restraints.

think of it this way: you kind of float out of your seat when a ride or rollercoaster train plummets. Technically you should fall at the same rate, right? but for some reason on a drop, if we weren't restrained, we would 'float' right out of our seats. Theoretically, we should fall at the same rate as the vehicle we are in, but I'm not so inclined to believe that. The car might very well reach the ground proportionally faster than we do.. ie, the distance between the vehicle and our body would continue to grow, thus the vehicle has to be traveling faster than our body.
Right?
Click to expand...

you float out of your seat because your leg muscles don't instantaneously stop supporting your weight. hence, you rise a bit, but then stop as you hit the restraints. a penny on your knee or water in a cup will not stop.
 
Originally posted by: destrekor
Originally posted by: Auggie
it's going to fall exactly the same speed as the riders, but the slightest jostle will give water upwards momentum since it's in a open-topped container, and since it's in a free fall like the rider, the upwards momentum is very noticeable, ie - the water floats up.

edit: to clarify - if they were able to hold the cup of water perfectly still, it wouldn't do that.
Click to expand...

can you explain why, in a similar situation (Demon Drop at Cedar Point), a coin placed on your knee, will 'float' above your knee as you drop?

hmm, as I was typing this, i figured it out.

the water will do that every time. Why? Because the cup actually should be falling at the same rate the water is, but the water isn't being contained, but the cup is (by being held). The body holding the cup? The body would also fall at the same rate as the water (thus, appear to float as compared to the vehicle the body is in as it falls at a slightly different rate). But the body is being held onto, by seatbelts and restraints.

think of it this way: you kind of float out of your seat when a ride or rollercoaster train plummets. Technically you should fall at the same rate, right? but for some reason on a drop, if we weren't restrained, we would 'float' right out of our seats. Theoretically, we should fall at the same rate as the vehicle we are in, but I'm not so inclined to believe that. The car might very well reach the ground proportionally faster than we do.. ie, the distance between the vehicle and our body would continue to grow, thus the vehicle has to be traveling faster than our body.
Right?
Click to expand...

Objects in motion stay in motion. Gravity accelerates you downward until you hit the restraints, which exerts a force to slow your downward acceleration. There is no force to counteract the downward acceleration of the coin until another object exerts a force on it.
 
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