Question on coriolis effect with drag force

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Discussion Overview

The discussion revolves around the trajectory of a small floating object on a liquid surface, influenced by drag and Coriolis forces at a given latitude. Participants explore the implications of a drag force that is linearly related to velocity and consider the scenario where drag is neglected.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks to determine the trajectory of an object under the influence of drag and Coriolis forces, questioning the effects of setting the drag coefficient α to zero.
  • Another participant asks for clarification on the variable "α," which is explained as a constant coefficient relating drag force to velocity.
  • It is noted that the drag force is described as being directly proportional to velocity, contrasting with typical drag equations that involve the square of velocity.
  • Some participants argue that the Coriolis force is perpendicular to the object's speed, suggesting that drag does not depend on the angle of motion, while others contend that drag is indeed influenced by the angle, especially in cases of sideslip.
  • A suggestion is made to perform a kinematic analysis considering all forces acting on the object, including Earth's rotation.
  • There is a discussion about the conditions under which the drag force might be linearly related to velocity, with references to low Reynolds number flows where viscous forces dominate.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the drag force and its relationship to velocity, with no consensus reached on the validity of the initial equation provided in the problem. The discussion remains unresolved regarding the implications of the drag force's dependence on velocity versus the square of velocity.

Contextual Notes

Participants highlight potential limitations in the problem's assumptions, particularly regarding the conditions under which the drag force is applied and the implications of neglecting drag.

ystch
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I really need help with this question.

A small floating object initially moves with velocity v on the surface of a liquid at latitude λ. The drag force due to liquid is F=-αv. Find the shape of the trajectory of the object due to drag and Coriolis forces. What will be the trajectory if α=0 ?
 
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What is "α"?
 
a would be a constant coefficient in this equation that relates drag force as a function of velocity.

the equation is of similar from as friction where F = u N.
 
The coriolis force is perpendicular to the speed, so the drag isn't influenced by the angle that the object is moving. You can solve a differential equation for the maginuted of the speed first: x'' = -ax'
 
256bits said:
a would be a constant coefficient in this equation that relates drag force as a function of velocity.

the equation is of similar from as friction where F = u N.

Then α has to be 1/2*ρ*Cd*S*u where ρ=density, Cd=coefficient of drag, S=the wetted area and u the velocity because drag is a function of the square of the velocity.

willem2 said:
The coriolis force is perpendicular to the speed, so the drag isn't influenced by the angle that the object is moving. You can solve a differential equation for the maginuted of the speed first: x'' = -ax'

The drag is indeed influenced by the angle that the object is moving. If it sideslips drag is higher than if it was moving with 0 angle from the longitudinal axis.


ystch,
If I were you, I would perform the kinematic analysis. Consider all forces acting on the object and take under consideration Earth's rotation as well.
α=0 means probably that you ignore the drag so you do the analysis once more neglecting drag.
 
Then α has to be 1/2*ρ*Cd*S*u where ρ=density, Cd=coefficient of drag, S=the wetted area and u the velocity because drag is a function of the square of the velocity.

The equation for the problem does not say that.
It says that the drag force has a direct relationship with velocity ( not velocity squared ).
 
256bits said:
The equation for the problem does not say that.
It says that the drag force has a direct relationship with velocity ( not velocity squared ).

I know. That's why I say that the equation given is wrong, unless the problem is not on Earth but somewhere else that drad could depend on the velocity and not on the square of the velocity ;) Under this assumption, he can proceed the solving procedure with the given equation.
 
Aero_UoP said:
I know. That's why I say that the equation given is wrong, unless the problem is not on Earth but somewhere else that drad could depend on the velocity and not on the square of the velocity ;) Under this assumption, he can proceed the solving procedure with the given equation.

Or it's on earth, in a flow condition dominated by viscous rather than inertial forces (a flow with a very low reynolds number).
 
cjl said:
Or it's on earth, in a flow condition dominated by viscous rather than inertial forces (a flow with a very low reynolds number).

Creeping flow... you're right, it slipped my mind.
I haven't dealt with such a flow for like a century :p lol
 

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