What atomic forces are acting to resist me pushing an air filled bottle underwater?

Greg Martin 05/15/2018. 2 answers, 290 views
forces pressure density buoyancy fluid-statics

Yes air is less dense than water but how does the bottle know to rise or indeed to move? It's not electromagnetism I think. Does this have a relation to gravitational forces? Is it to do with the number of protons in the molecules of the different substances?

2 Answers

Ben51 05/15/2018.

The microscopic explanation for the macroscopic phenomenon of pressure is that momentum is transferred by electromagnetic forces from individual fluid particles (in this case, water molecules) to anything they approach closely enough, including other water molecules or the molecules of plastic that make up the bottle. The momentum transferred by a single water molecule to the bottle during an interaction depends on the details of that interaction, but you don't have to resolve those details to say something about the total amount of force--for that you only need a statistical description of the sum total of all the interactions, which is what pressure is.

So, why is the force exerted on the bottom of the bottle by all these collisions greater than that exerted on the top? Because of gravity and the mass of the overlying water, the water molecules further from the surface are packed slightly more closely together on average than the ones closer to the surface. Their mutual repulsion is therefore greater on average--this repulsive electromagnetic force grows very quickly as water molecules move closer together. The water molecules closest to the bottle are squeezed a bit closer to it where the pressure is greater (deeper below the surface), transmitting the higher average intermolecular repulsive forces there to the surface of the bottle.

my2cts 05/15/2018.

Archimedes figured this one out around 250 BC. If you push an empty bottle underwater you have to raise the surface of the water by the same volume. This is the counterforce that you feel.

HighResolutionMusic.com - Download Hi-Res Songs


Kiss And Make Up flac

BLACKPINK. 2018. Writer: Soke;Kny Factory;Billboard;Chelcee Grimes;Teddy Park;Marc Vincent;Dua Lipa.
2 Martin Garrix

Waiting For Tomorrow flac

Martin Garrix. 2018. Writer: Pierce Fulton;Mike Shinoda;Martijn Garritsen;Brad Delson.
3 John Legend

Written In The Stars flac

John Legend. 2018. Writer: Kiana Brown;Santoy;Kevin White;Mike Woods;MZMC;The Heavy Group;Rice N' Peas.
4 Alan Walker

Diamond Heart flac

Alan Walker. 2018. Writer: Alan Walker;Sophia Somajo;Mood Melodies;James Njie;Thomas Troelsen;Kristoffer Haugan;Edvard Normann;Anders Froen;Gunnar Greve;Yann Bargain;Victor Verpillat;Fredrik Borch Olsen.
5 Bradley Cooper

Shallow flac

Bradley Cooper. 2018. Writer: Andrew Wyatt;Anthony Rossomando;Mark Ronson;Lady Gaga.
6 Martin Garrix

Access flac

Martin Garrix. 2018. Writer: Martin Garrix.
7 Cardi B

Taki Taki flac

Cardi B. 2018. Writer: Bava;Juan Vasquez;Vicente Saavedra;Jordan Thorpe;DJ Snake;Ozuna;Cardi B;Selena Gomez.
8 Martin Garrix

Yottabyte flac

Martin Garrix. 2018. Writer: Martin Garrix.
9 Post Malone

Sunflower flac

Post Malone. 2018. Writer: Louis Bell;Billy Walsh;Carter Lang;Swae Lee;Post Malone.
10 Lady Gaga

I'll Never Love Again flac

Lady Gaga. 2018. Writer: Benjamin Rice;Lady Gaga.
11 Bradley Cooper

Always Remember Us This Way flac

Bradley Cooper. 2018. Writer: Lady Gaga;Dave Cobb.
12 Mako

Rise flac

Mako. 2018. Writer: Riot Music Team;Mako;Justin Tranter.
13 Dyro

Latency flac

Dyro. 2018. Writer: Martin Garrix;Dyro.
14 Avril Lavigne

Head Above Water flac

Avril Lavigne. 2018. Writer: Stephan Moccio;Travis Clark;Avril Lavigne.
15 Sia

I'm Still Here flac

Sia. 2018. Writer: Sia.
16 Halsey

Without Me flac

Halsey. 2018. Writer: Halsey;Delacey;Louis Bell;Amy Allen;Justin Timberlake;Timbaland;Scott Storch.
17 Deep Chills

Run Free flac

Deep Chills. 2018.
18 Julia Michaels

There's No Way flac

Julia Michaels. 2018. Writer: Ian Kirkpatrick;Justin Tranter;Julia Michaels;Lauv.
19 Rita Ora

Let You Love Me flac

Rita Ora. 2018. Writer: Rita Ora.
20 Zara Larsson

Ruin My Life flac

Zara Larsson. 2018. Writer: Delacey;Michael Pollack;Stefan Johnson;Jordan Johnson;Sermstyle;Jackson Foote.

Related questions

Hot questions


Popular Tags