Understanding Brownian Motion: The Theory Behind Random Particle Movement

  • Context: Undergrad 
  • Thread starter Thread starter bobsmith76
  • Start date Start date
  • Tags Tags
    Brownian motion Motion
Click For Summary

Discussion Overview

The discussion revolves around the nature of Brownian motion and the underlying reasons for the random movement of particles. Participants explore theoretical explanations, the role of collisions, and the implications of forces acting on particles at the atomic level.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the explanation of random particle movement as merely leftover energy from the Big Bang, suggesting it does not account for the randomness of paths.
  • Another participant describes Brownian motion as a result of particles undergoing numerous collisions, likening it to bumper cars, where the direction changes due to interactions with other particles.
  • A participant raises the idea that particles might change direction without an apparent reason, prompting a response that asserts a force must act on them for such changes to occur.
  • One participant emphasizes that random direction changes would violate conservation of momentum, indicating a need for forces to be involved in particle movement.
  • Another participant questions whether atomic-level behavior differs from classical mechanics, suggesting that collisions at this scale might not conform to the same rules as larger objects like billiard balls.
  • A response clarifies that particles do not move randomly but rather in fixed directions determined by collisions, countering the notion that they "choose" their paths.

Areas of Agreement / Disagreement

Participants express differing views on the nature of particle movement, with some agreeing on the necessity of forces for direction changes, while others question the applicability of classical mechanics to atomic behavior. The discussion remains unresolved regarding the implications of these viewpoints.

Contextual Notes

There are limitations in the assumptions made about atomic behavior and the definitions of randomness and forces at play in particle interactions. The discussion does not resolve these complexities.

bobsmith76
Messages
336
Reaction score
0
Is there a theory regarding why particles move in random paths. My high school physics teacher said it's energy left over from the big bang, but that doesn't explain why they move in random paths, they could just as easily obey Newton's Laws of Motion and still have energy left over from the Big Bang.
 
Physics news on Phys.org
Aaaaah! They said WHAT?!

Here is a good place to start on http://en.wikipedia.org/wiki/Brownian_motion" .

On the scale of individual molecules, particles are rapidly undergoing collisions for all of the other particles. Its like bumper cars. A particle will get bumped in one direction, then it will get bumped in another, and another... and you end up with 'brownian motion' or the 'random walk'.

On larger scales, like small dust particles, brownian motion can still be important. For particles as large as dust, TONS and TONS of particles are ALWAYS bumping into them from all sides. Every once and a while they get bumped a little extra hard in one direction, however, and then a fraction of a second later, they get bumped extra hard in another direction----thus they also can undergo brownian motion.

Hope that helps; and let me know if you still have questions.
 
Last edited by a moderator:
But I thought particles could change direction for no reason. Is that true?
 
No they would have to have a force acting upon them to do this
 
rc1102 is correct.
Note that if they did randomly change directions, that would violate conservation of momentum.
 
What was conservation of momentum, I vaguely remember it but can't remember the details
 
I'm talking about on the atomic level. Aren't things different on the atomic level? Or is it just when they crash into another atom they do not behave as billiard balls and fly at any angle they choose?
 
Billiard balls and particles do not move in a random direction they move into a fixed direction given by a collision. That is not random and so they do not "choose" a direction move in.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
4K
  • · Replies 15 ·
Replies
15
Views
1K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 30 ·
2
Replies
30
Views
2K