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If I was kicking a soccer ball on another planet in our solar system, besides gravity what other factors would impact its flight path? For example, is the drag the same? (Assuming the ball pressure remains constant. ) Where would I find estimates of planetary differences in drag? Thank you for your consideration of my question. Regards.
Question Date: 2016-01-01
Answer 1:

That is a great question. Gravity is, of course, different, and can be stronger or weaker, depending on the planet. The drag on the ball will also change, depending on the pressure of the atmosphere, the temperature on the surface, and the type of gas in the atmosphere. There is a nice website from NASA

click here

that talks about aerodynamics on other planets.

The density and viscosity of the gas in the atmosphere are the main material properties required to figure out the drag force on the ball. This depends on the type of gas, the pressure of the gas, and the temperature. Once you have the viscosity (and density) of the gas, and if you figure out how fast you can kick a ball, and how big a ball you’re kicking, you can figure out the “Reynolds number” for that ball. This is a quantity that is very important in fluid dynamics and gas dynamics, and determines how the fluid behaves. From the Reynolds number, you can figure out a “drag coefficient” for the ball,


which tells you how big the drag force is on the ball.

Generally, the drag force will be

F = CD * rho * V2 where rho is the density of the gas, CD is the drag coefficient (from the figure on the website above), and V is the velocity (or speed) of the ball.

Most of the time, CD will be between 1.5 and .5 — so doesn’t depend very strongly on the Reynolds number (or viscosity), although there are conditions where viscosity will really matter (where CD is much bigger or much smaller). So most of the time, the main difference in drag force on a ball kicked at 30 mph on Earth vs. on Mars will come from the difference in atmospheric densities (rho) on the two planets.

Play around on the NASA website — there are lots of interesting details about other planets, that make you realize how different even everyday life can be...

Answer 2:

The density of the atmosphere determines drag. Most sources that would tell you what the surface gravity of a planet is would also tell you some things about the planet's atmosphere.

Incidentally, I don't know how much drag affects soccer ball kicks. However, here's something for you to check out: South American peoples play soccer on the Altiplano, a plateau in the Andes mountains at about 3,000 meters elevation. The air pressure at that altitude is about 80% or so of the pressure at the surface, ballpark. Does this affect drag noticeably?

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