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According to one explanation, the left hand acceleration terms of Navier Stokes equations are the called the inertial terms. If you were to balance forces on the fluid particle, they would have to be equal and opposite to the forces on the right hand side (pressure gradient, viscous, and body). To me it seems like you're in the non-inertial reference frame of the fluid particle and treating the inertial force as a fictitious force in this reference frame. Is this at all accurate?

Another explanation I thought I heard is that the inertial force is due to dynamic pressure only. Is this at all accurate (is it an approximation of the previous description)?

On a slight tangent, when finding Reynold's number, the inertial term is ##\rho V^2##. If all fluid particles of a dense fluid were moving at a high but constant velocity, this term should be very large. However, the acceleration is 0, and so shouldn't the inertial force be 0?

Another explanation I thought I heard is that the inertial force is due to dynamic pressure only. Is this at all accurate (is it an approximation of the previous description)?

On a slight tangent, when finding Reynold's number, the inertial term is ##\rho V^2##. If all fluid particles of a dense fluid were moving at a high but constant velocity, this term should be very large. However, the acceleration is 0, and so shouldn't the inertial force be 0?

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