# Wright State University Lake Campus/2018-1/Ping pong air drag

## From Wikipedia permalinks

##### w:Reynolds number @ w:special:permalink/822809548
A w:vortex street around a cylinder. This can occur around cylinders and spheres, for any fluid, cylinder size and fluid speed, provided that the flow has a Reynolds number between roughly 40 and 1000.
Pressure dependence of the dynamic viscosity of dry air at the temperatures of 300, 400 and 500 kelvins

The Reynolds number is defined as

${\displaystyle \mathrm {Re} ={\frac {\rho uL}{\mu }}={\frac {uL}{\nu }}}$

where:

• ${\displaystyle \rho }$ is the w:density of the fluid (SI units: kg/m3)
• ${\displaystyle u}$ is the velocity of the fluid with respect to the object (m/s)
• ${\displaystyle L}$ is a characteristic linear dimension (m). For a sphere L=2R is the diameter.
• ${\displaystyle \mu }$ is the dynamic viscosity (Pa·s or N·s/m2 or kg/m·s)
• ${\displaystyle \nu }$ is the kinematic viscosity (m2/s).
##### w:Viscosity @ w:special:permalink/824605819#Air

The viscosity of air depends mostly on the temperature. At 15 °C, the viscosity of air is 1.81x10−5 kg/(m·s) 18.1 μPa·s or 1.81x10−5 Pa·s. The kinematic viscosity at 15 °C is 1.4810x10−5m2/s or 14.8 cSt. At 25 °C, the viscosity is 18.6 μPa·s and the kinematic viscosity 15.7 cSt.

Here, 1 cSt = 1 mm2·s−1 = 10−6 m2·s−1.

##### w:Drag (physics) @ w:special:permalink/823381084
${\displaystyle F_{D}\,=\,{\tfrac {1}{2}}\,\rho \,v^{2}\,C_{D}\,A}$

## Original effort circa 2/1/18

From this graph we estimate an acceleration of 7 cm/s/s at a speed of 50 cm/s.

## 2/8/18 Thursday phy2400 lab

We will attempt to simulate this with Matlab:

I think we did the Reynold's number thing wrong. I get Re=300 here, and that means C =1 here

Ping pong ball: radius = 20mm; mass=2.7g