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183_notes:drag [2021/02/04 23:36] – [Fluid Resistance] stumptyl | 183_notes:drag [2021/02/04 23:39] (current) – [Models of fluid resistance] stumptyl | ||
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//An object moving in any fluid experiences some form of resistance to its motion due collisions with molecules of the fluid.// Each of these little collisions with the surrounding fluid contribute to the overall resistive force that the fluid exerts on a moving object. | //An object moving in any fluid experiences some form of resistance to its motion due collisions with molecules of the fluid.// Each of these little collisions with the surrounding fluid contribute to the overall resistive force that the fluid exerts on a moving object. | ||
- | Unlike friction forces, which are velocity-independent, | + | //Unlike friction forces, which are velocity-independent, |
==== Models of fluid resistance ==== | ==== Models of fluid resistance ==== | ||
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=== Laminar drag === | === Laminar drag === | ||
- | For a situation where the Reynolds | + | For a situation where the __Reynolds |
$$\vec{F}_{drag} = -b\vec{v}$$ | $$\vec{F}_{drag} = -b\vec{v}$$ | ||
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$$\vec{F}_{drag} = -6\pi\eta r \vec{v}$$ | $$\vec{F}_{drag} = -6\pi\eta r \vec{v}$$ | ||
- | where $\eta$ is the fluid viscosity. | + | where** $\eta$** is the **fluid viscosity**. |
+ | \\ | ||
=== Turbulent drag === | === Turbulent drag === | ||
- | For a situation where the Reynolds | + | For a situation where the __Reynolds |
$$\vec{F}_{drag} = -cv^2\hat{v}$$ | $$\vec{F}_{drag} = -cv^2\hat{v}$$ | ||
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$$\vec{F}_{drag} = -\dfrac{1}{2} \rho C_d A v^2 \hat{v}$$ | $$\vec{F}_{drag} = -\dfrac{1}{2} \rho C_d A v^2 \hat{v}$$ | ||
- | where $\rho$ is the density of the fluid, $A$ is the cross-sectional area of the object in the fluid, and $C_d$ is the drag coefficient of the object, which is often measured experimentally. | + | where $\rho$ is the// density of the fluid//, $A$ //is the cross-sectional area of the object in the fluid//, and $C_d$ //is the drag coefficient of the object, which is often measured experimentally//. |
+ | \\ | ||
=== What about " | === What about " | ||