**Just after jumping out, the instructor throws out a large (approx. 4-foot/1.2-m diameter) drogue chute, and this drogue is out during the entire free fall. Without this drogue, the combined weight of the instructor and student would cause the pair to fall at 180 to 200 mph (290 to 320 kph) – much faster than the normal 120 mph. The drogue slows the pair down to the normal falling speed. **
http://travel.howstuffworks.com/skydiving1.htm
I was reading this and wondered how this works. I always thought that once you reach terminal velocity, you cannot go any faster. I also thought that two objects fall at the same speed no matter what their weight. What’s the SD?
Terminal velocity is dependent upon a number of factors, like surface-to-mass ratio (surface, in this case being the surface facing downward). With two people jumping in tandem you’ve approximately doubled the mass, but the wind-load surface area isn’t changed much, so the pair has a higher terminal velocity than either alone.
I didn’t read the cite but I assume they mean that when you strap two people together, with one in front of the other like they do, that you have twice the weight, and the same downword facing profile.
This means you get to fall faster than one person. Not twice as fast as drag becomes s^2 thing approaching some speed.
Think of it as the second guy drafting behind the first guy, so has basically no force on him from the air resistance, he ends up laying on top of the first guy, pushing him even faster.
If they were not on top of each other, but next to each other, the terminal velocity would be much closer to that of an individual. I’m sure it would not be exactly the same though. I don’t know enough about airflow to know if they would fall faster or slower when side by side.
So what was the story with Gallileo dropping the two objects off the leaning tower of Pisa? I thought they they both hit the ground at the same time. So if the tandem jumpers and another skydiver left the plane at the same time, how is it that one will fall faster than the other. Sorry to be so dense, but this is really bugging me and I can’t seem to get my head around it.
Dropping objects off the leaning Tower isn’t quite the same, since the objects don’t have time to reach terminal velocity (which for a cannonball would be really fast anyway), and they do hit the ground at the same time (unless one is a feather or something).
Let’s say a single jumper and a pair pf tandem jumpers exit the plane simultaneously. Initial, both the single, and the tandem pair will accelerate the same and fall together. However, eventually the single will reach his termanal velocity, say, at 120 MPH, and stop accelerating. He’ll stay at that speed until he opens his chute (or smushes into the ground). Meanwhile, at 120 MPH, the tandem jumber, having more mass, but the same wind-load surface area, will continue to accelerate until they reach their terminal velocity, at say, 170 MPH.
It was a story to illustrate that gravity ACCELERATEs things the same no matter what they weigh, their size, their shape, or how dense they are. Gravity though, produces FORCE, directly proportional to the weight and cares not about the density, size or shape…
Air resistance is not nearly so understanding though. Air resistance is directly related to the size and shape of things and cares not about the weight or density.
Tandem jumpers have a shape very similar to a solo jumper so air resistance treats them about the same. Gravity however exterts more force on the tandem jumpers (more weight, more force) than the solo jumpers so the tandem falls faster.
…To the rest of you, please no comments about the weight and force being the same. I am treating mass and weight here the same to facilitate the answer to the OP, not working on a theisis.
The bit about “all objects fall at the same rate” is only true if air resistance is not significant. Consider a hammer and a feather: The feather definitely does fall slower, because of air resistance. And whenever you’re talking about parachutes or terminal velocity, air resistance is definitely significant.
