- #1

Florian Geyer

- 94

- 16

- TL;DR Summary
- Why is fluid equilibrium based on Newton's first and third laws?

Hello respected members,

I have been studying Sears and Zemansky's university physics, and I have encountered the following statement.

Here is my try:

- Newton's first law: like the case of rigid body equilibrium the net external force exerted on the fluid must be zero, so that the fluid remains in its state of liner motion.

- Newton's third law: I am really lost here nor I could understand why this law is important in this regard.

- Also, may I ask what is the equivalent of the condition of zero torque like the case of rigid body equilibrium? you may say that there is such thing as torque in the case of fluids since there is no "lever arm" but how about the case of vortexes the net force -as I understand- is zero, but the fluid still in motion, or shall we consider a fluid with vortexes as a fluid in a state of equilibrium?

I have been studying Sears and Zemansky's university physics, and I have encountered the following statement.

I could not understand it well, so my question is: Why is fluid equilibrium based on Newton's first and third laws?We begin our study with fluid statics, the study of fluids at rest in equilibrium situations. Like other equilibrium situations, it is based on Newton’s first and third laws. We will explore the key concepts of density, pressure, and buoyancy.

Here is my try:

- Newton's first law: like the case of rigid body equilibrium the net external force exerted on the fluid must be zero, so that the fluid remains in its state of liner motion.

- Newton's third law: I am really lost here nor I could understand why this law is important in this regard.

- Also, may I ask what is the equivalent of the condition of zero torque like the case of rigid body equilibrium? you may say that there is such thing as torque in the case of fluids since there is no "lever arm" but how about the case of vortexes the net force -as I understand- is zero, but the fluid still in motion, or shall we consider a fluid with vortexes as a fluid in a state of equilibrium?