Can Brownian Motion Suspend Larger Particles in a Denser Fluid?

In summary, the conversation discusses the calculation of the maximum size of a particle that can be suspended by Brownian motion in a fluid. The equation kT>mgd is used, where kT is thermal energy, m is the mass of the particle, g is gravity, and d is the particle's typical size. The mass of the carrier fluid particles is accounted for through viscosity and temperature. The equation is in units of joules and kT represents the energy of one particle. The conversation ends with a mutual appreciation for physics.
  • #1
Warpspeed13
125
2
I was reading about ferrofluid and I was wondering how you would go about calculating the maximum size of a particle that could be suspended by Brownian motion in a fluid? Can a denser fluid suspend larger particles?
 
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  • #2
The response is: kT>mgd, where kT is thermal energy, m the mass of the particle, g is gravity and s is the particle typical size. When thermal energy is smaller sedimentation will occur.
 
  • #3
mpelaez83 said:
The response is: kT>mgd, where kT is thermal energy, m the mass of the particle, g is gravity and s is the particle typical size. When thermal energy is smaller sedimentation will occur.

Cool. How would the mass of the carrier fluid particles be accounted for? It seems mercury would be different than water.
 
  • #4
You actually account for that through viscosity in some way. The carrier fluid as you call it is accountef by a viscosity and a temperature, the system temperature
 
  • #5
These are deep questions people don't ask so there are a lot of reasonable misconceptions.
 
  • #6
Cool thanks for the help
 
  • #7
mpelaez83 said:
You actually account for that through viscosity in some way. The carrier fluid as you call it is accountef by a viscosity and a temperature, the system temperature
Sorry but what units were you're original equation in, I assumed it was jules> kg* 9.82* surface area in m^2
 
  • #8
g has units of m/s^2, d is in meters and m is in kg. Then you get joules.
 
  • #9
mpelaez83 said:
g has units of m/s^2, d is in meters and m is in kg. Then you get joules.
Is kT the energy of one carrier fluid atom or the energy of the system?
 
  • #10
kT is the energy associated to one particle. When i say particle you can think on both the solvent molecules or the dispersed particles. The energy of a thermodynamic system it depends on and adittional thermodynamic variable, partiole number N. For example in an ideal gas the energy of the system is ~NkT
 
  • #11
Cool thanks for the help
 
  • #12
No problems. Physics is cool.
 
  • #13
Yep.
 

1. What is Brownian motion?

Brownian motion is the random movement of particles suspended in a fluid. This phenomenon was first observed by Robert Brown in 1827, hence the name. It is caused by the constant collisions of the particles with the molecules of the fluid, which results in their erratic movement.

2. What causes Brownian motion?

Brownian motion is caused by the constant collisions of particles with the molecules of the fluid they are suspended in. These collisions are random and unpredictable, resulting in the particles' erratic movement.

3. How is Brownian motion related to temperature?

The rate of Brownian motion is directly related to temperature. As temperature increases, the molecules of the fluid move faster, resulting in more frequent and energetic collisions with the suspended particles, leading to increased Brownian motion.

4. What is the significance of Brownian motion in science?

Brownian motion is significant in science because it provides evidence for the existence of atoms and molecules, which were once thought to be theoretical. It is also used to study the properties of fluids and is an important concept in fields such as chemistry, physics, and biology.

5. Can Brownian motion be observed in everyday life?

Yes, Brownian motion can be observed in everyday life. Examples include the movement of dust particles in the air, the dispersion of ink in water, and the movement of smoke particles. It is also the driving force behind the diffusion of substances in and out of cells in living organisms.

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