pbuk said:
That is not an answer to the question in the OP, but if you are asking "will an object with a higher density fall faster than an object with a lower density" then consider a bottle full of water suspended under a parachute and a bottle half full of water with no parachute. Which one has the higher density? Which one falls faster?
Changing the question half way through to make my answer look wrong is really just a bad explanation.
Higher density was a hint to help work out the answer - OP has to make an intelligent guess to which one has the higher density.
For a start, you are deliberately ignoring the mass of the parachute in your rebute (the ones I had for my aircraft were about 15lbs, the one I had on my back on Saturday and Sunday was 18lbs, but I didn't have to jump out, of course)
You are ignoring the volume occupied by the parachute.
You are well aware that the shape of the parachute influences the drag, and I bet you know that a big parachute that doesn't open properly and gets entangled with itself will
probably mean the user falls faster than someone using a parachute with 10% smaller total surface area but fully opened. (unless we are talking about tiny parachutes that just will not work)
You are ignoring that as a pilot I am very well aware of the effect of drag in its various types. Your answer is aimed directly at form drag (one type of parasitic drag) - caused by the shape of the object. Form drag, as we all know, increases with speed
Then you reach the same answer as me and say
"the tennis ball falls faster because it has
less air resistance in relation to its mass than the feather", or in the terminology of the OP and noting that air resistance is closely related to surface area, "the tennis ball falls faster because it has less surface area in relation to its mass than the feather".
Which is saying the object with the greater density has less drag per unit volume, although the shape and hence drag will complicate things a little bit.
So have a read of my example featuring table tenis ball, wooden ball and steel ball. I know that you will get the correct answer to which will reach the highest velocity, assuming the slope is long enough for all the objects to reach their teminal velocity. But even on a medium length slope, say 10 or 15 or so metres in length, with no ball carrying a parachute just to make things clearer, we both know which one will be traveling fastest at the 10 metre mark - "The one with less air resitance in relationship to its mass". The most dense of the three.Now here's an interesting one, where many glider pilots get the right answer to the first half but give the wrong reason for their answer, but I suspect you will get it correct.
Two identical gliders (ie same model, same shape, same empty mass), with identical weight pilots are flying at the same speed (we will say fast, say 100 knots, to make this more straightforward). And are flying together at the same height. But one glider has 100kg of water ballast in each wing, the other has no water ballast on board (not any other type of ballast). Both pilots pull back on the control column by the same amount / same angle / same stick movement at the same 100 knots speed, and not at an angle that risks stalling the aircraft due to excessive g loading and huge angle of attack. And they dont' adjust the glider's flaps, either. I think I've covered all excuses or silly things and variations that would mess things up.
So.
Which one will pull up by the largest amount, and why?
(Or do they both pull up to the same height?)
Remember PE = mgh and KE = 1/2mv
2
h = height of course.
Gone on, give it a try, but the reason why is the important bit ;)
