Phys Lab 7

# Phys Lab 7 - Determining the Effect of Air Resistance on...

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Determining the Effect of Air Resistance on Falling Coffee Filters John Domanick 11/9/10 Partner: Matt Wiener Teaching Fellow: Tim Harden

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Abstract: In this experiment we investigated the effects of air resistance in the lab, an effect that is normally ignored. We will observe the motions of several coffee filters as they fall, to determine the type of airflow that results. Theoretically we know that the force of air resistance at terminal velocity is related to both the magnitude of velocity and the type of airflow, by the equation:
We know that n=1 for laminar, or smooth flow, and n=2 for turbulent flow. By measuring the terminal velocities of different masses of coffee filters we found that the airflow about the filters in the lab was a turbulent flow, with n=2.393+/-0.373. Theory: In most cases, we can categorize the resistive force an object experiences moving through a fluid as laminar or turbulent. Laminar flow is characterized by the smooth flow of layers of the fluid around the object, each layer moving at the equal velocity. The layers do not cross and do not interact with one another. Turbulent flow occurs when the smooth flow of the fluid molecules is bothered so that the flow lines cross. Molecules in different laminae then interact by scattering off one another and whatever object is causing the disturbance. The fluid flow becomes disorganized. Laminar flow takes place at low speeds and turbulent flow at high speeds. A perfect sphere is an idealized model that can be utilized to find the drag forces of laminar and turbulent flow. For a sphere moving through a fluid by laminar flow, the following equation for the Resistant Force also known as Stoke’s Law has been determined using Fluid Dynamics: (1) Where r is the radius of the sphere, v is the velocity of the sphere relative to the fluid, and n is the viscosity of the fluid. There is also an equation that relates velocity to the resistant force for a sphere undergoing turbulent flow: (2) where v is the velocity of the sphere relative to the fluid, ρ is the density of the fluid, and C d is the drag coefficient.

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## This note was uploaded on 10/06/2011 for the course PHYS 19 taught by Professor Blocker during the Fall '10 term at Brandeis.

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Phys Lab 7 - Determining the Effect of Air Resistance on...

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