Drag - Terminal Velocity of a solid sphere.

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SUMMARY

The discussion focuses on calculating the terminal velocity of a solid sphere with a diameter of 20mm and a specific gravity of 1.3 when dropped in water with a viscosity of 1*10^-3 and a density of 1000 kg/m³. The approach involves estimating the drag coefficient, determining the Reynolds number, and iteratively refining the guess for terminal velocity. Key equations include the drag force equation Fd=(1/2)*Cd*ρ*(U^2)*A, where Cd is the drag coefficient, ρ is the fluid density, U is the velocity, and A is the cross-sectional area of the sphere. The discussion emphasizes the importance of using reliable resources for kinematic viscosity, Reynolds number calculations, and drag coefficients.

PREREQUISITES
  • Understanding of fluid dynamics concepts, specifically terminal velocity.
  • Familiarity with the drag force equation and its components.
  • Knowledge of Reynolds number and its significance in fluid flow.
  • Basic grasp of kinematic viscosity and its role in fluid mechanics.
NEXT STEPS
  • Research the calculation of terminal velocity for different shapes and conditions.
  • Learn how to compute the Reynolds number for various fluid scenarios.
  • Study the relationship between drag coefficients and Reynolds numbers for spheres.
  • Explore resources on kinematic viscosity of fluids and its impact on motion.
USEFUL FOR

Students in physics or engineering, researchers in fluid dynamics, and professionals involved in designing systems where drag forces are significant will benefit from this discussion.

MrWinesy
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Homework Statement



A solid sphere - 20mm in diameter, σ (specific gravity) = 1.3

dropped in water μ=1*10^-3 and ρ=1000

determine the terminal velocity for the sphere.

(hint- guess the value for the drag coefficient then iterate)


Homework Equations



Fd=(1/2)*Cd*ρ*(U^2)*A

The Attempt at a Solution



tried guessing the drag coefficient but have no confidence in estimate or of the next step.

(also the relationship equation connecting viscosity, specific gravity and density would be much appreciated).

Thank you in advance for your help.
 
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What they have in mind I guess is this:
1. guess at the terminal velocity.
2. determine the Reynolds number for a sphere in water at that velocity.
3. Determine the drag coefficient based on the Reynolds number.
4. Compute the drag force based on c and v.
5. Compare with your guess of v.
6. Re-guess v etc.

There are several Websites that together can give you all the info you need:
1. kinematic viscosity of water
2. Reynolds number for a sphere at a given velocity
3. Drag coeff. as a function of the Reynolds number for a sphere.

Along the way you can pick up any theory and data you didn't know.
 

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