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The Coefficient of air resistance is not unitless, it is in the units of kg/m because the speed squared is in m^2/s^2 and when multiplied by kg/m you get (kg m)/s^2 which is Newtons. That is in fact what the coefficient does, it converts from speed squared to newtons while applying a coefficient of proportionality.


Oh no! Getting called out on my physics knowledge (which is a bit rusty).


Do you remember where I say this in the video so that I can correct it?



To start let me say AWESOME tutorial :slight_smile: I am having a blast with it, and
learning a TON, great job. The mistake in question is on section 4,
lecture 74, 8:36 into the lecture when you are talking about the formula
for air resistance.

Best Wishes,



Cool, it should be uploading now.


Hey, I finished the tutorial series. Great job Sam, really enjoyed all of it and it is helping me in my product that I am working on. But, I always got confused on this part when talking about the drag coefficient unit.

According to wikipedia, the coefficient of air resistance is indeed dimensionless or unit-less. The Drag Force is what is (kg*m)/s^2, or equivalently “Newtons.”

I think this confusion that Bill had stemmed from the original formula, as we discussed it. It should be like this:


which includes DragArea.

So, to fix this in the code we would have the following:

   //DragCoefficient is indeed unitless! 0.3f - 0.5f is generally good to use. 0.3f - Tanks, 0.5f - Automobiles
		float DragCoefficient = 0.5f;
	//The DragArea that is (cm^2). Higher means more drag
		float DragArea = 20000.f;

Which, then we would multiply in our GetAirResistance() function.

Hopefully this makes sense.


Yes, I think I was making it less physical in the course to simplify the equation to F is proportional to v^2 with C being the constant between them which would include rho, 1/2 and A