Simple, everyday science

[Perfection]

Using a straw, you can drink a glass of water. However, if you were to go to the third floor of a building and try to drink a glass of water on the sidewalk below, using a very long straw, you would find you can't do it. Why?

I wouldn't be surprised if you could. Let's say the third floor is around 22 feet, that would require about a 35% vacuum, which seems doable. Of course getting it above 34 feet is imposible at standard atmopheric conditions and suction being the only raising factor.

 

[El_Machinae]

Because the amount of liquid you're pulling up the straw is very little, normally. Anything below the water line essentially weighs nothing.

However, to drink from a third story floor would require you to suck up the whole 500g of water, when we're used to sipping only about 15g at a time.

If you sucked for a bit, lifted the straw above the glass, and continued sucking (so you only had 15g at a time), you'd be fine.

 

[RoddyVR]

the last two responses have now finaly settled in my mind that whole mess with "trees shouldnt be able to grow over 34 feet", "but they do".

"Thank You!" to perfection and el machine.

 

[Bozo Erectus]

This is really simple, basic stuff for you guys but its one I could never understand:

What does a rocket in the vacuum of space push against?

 

[Truronian]

Perhaps its just that the walls of the straw will collapse before the water is all the way up.

 

[Truronian]

This is really simple, basic stuff for you guys but its one I could never understand:

What does a rocket in the vacuum of space push against?

Its exhaust fumes.

 

[El_Machinae]

The two atoms repel against each other, and go in two different directions. They each have mass and velocity, ergo, momentum. One of the atoms goes out the exhaust, hurtling through space for even. The other impacts the bottom of the rocket ship, imparting the momentum into the rocket.

If I was on roller skates, and threw billiard balls at you, I would roll backwards (being one half of the explosion) and you would be pushed away from me (being the victim of the other half of the explosion).

 

[thetrooper]

This is really simple, basic stuff for you guys but its one I could never understand:

What does a rocket in the vacuum of space push against?

Actio et inactio.

 

[Bozo Erectus]

I dont doubt it, I just dont get it. Seems like climbing by pulling on a rope that isnt attached to anything.

 

[bathsheba666]

It doesn't push against anything..
..but neither is there anything pushing against the rocket to keep it in one place.

Momentum in the system has to be conserved, so if one mass is thrown 'back', the other mass has to move 'forward'.

So (just for example, roughly) if the fuel exhaust sheds 1kg fuel moving at 100m/s, then the body of the rocket (100kg) moves the other way at 1m/s.

 

[El_Machinae]

Does mine make sense? Remember that the explosion is actually gazillions of atoms being repelled from each other. Some of them go out the back, some of the hit the rocket and move it forward.

 

[Bozo Erectus]

If I was on roller skates, and threw billiard balls at you, I would roll backwards (being one half of the explosion) and you would be pushed away from me (being the victim of the other half of the explosion).

The billiard balls being atoms?

 

[El_Machinae]

Yeah. And my arm is the explosion, and me (on the roller skates) are more atoms.

 

[Che Guava]

Precisely! The expansion of the gas, even though it doesn't push against anything, still pushes the rocket forward.

 

[Bozo Erectus]

Ok thanks guys, I'll think about all that over lunch and see if I can grok it

 

[Truronian]

Another one:

Can you design a room with mirror walls such that no light from a lamp at A reaches a camera at B (where A and B are specified points in this room)?

 

[El_Machinae]

Not easily: you'd have to make the lamp reabsorb all the photos before they deviated enough from their path (due to the diffusion), except for diffusion required to go below the 1 photon threshold.

Unless you designed the room like a tube, and the lamp took up the whole tube, putting the camera behind it.

 

[thetrooper]

@ SPOCK, Truronian: I thought this thread was about everyday science?

 

[Che Guava]

Wouldn't you need some a laser for that, seeing as how most light will spread out more randomly?

 

[El_Machinae]

Lasers diffuse, just like normal light does. We just don't notice, because they don't diffuse much in the distances we use them.