4 ms·

"Lower body weight reduces terminal velocity," How does this work?

Nursie 10y ago
Air resistance affects lighter stuff more, proportionally, and gives it a lower terminal velocity. A mouse can be dropped and survive (maybe with broken limbs) from almost any height, as there's not a lot of mass behind it and the air will keep it from going too fast. This is in contrast to the Galilean experiment where you drop two things and they fall at the same rate regardless of mass - this is true in a vacuum but not in atmosphere.
- barrkel 10y ago
  "Air resistance affects lighter stuff more" This is nonsense. Air resistance is caused by drag and has nothing to do with weight. An arrow will fall faster to the ground than big balloon, despite weighing the same.
  - PhasmaFelis 10y ago
    It's awkwardly phrased, but it's pretty clear what they intended from the rest of the comment.
  - Nursie 10y ago
    "This is nonsense. Air resistance is caused by drag and has nothing to do with weight. An arrow will fall faster to the ground than big balloon, despite weighing the same." But if you had two arrows of different weights, air resistance would act to slow the lighter one more. So no, it's not nonsense.
arnarbi 10y ago
Like a ping-pong ball vs a golf ball. The gravitational force is smaller on a light object, so less drag is required to counter it. Being the same shape, that drag is reached at a lower speed than for the heavy object.
barrkel 10y ago
Gravitational force is proportional to mass; in a vacuum, the only thing that stops heavier things from falling faster is the fact that acceleration due to applied force is inversely proportional to mass, so the mass cancels out. Drag is proportional to cross-sectional area and the square of the velocity; mass doesn't factor in. There are two main forces on the falling object, then: gravity pulling it down, and drag pushing it up. Terminal velocity is reached when both are equal. Lower mass means less gravity, but drag is unaffected. Thus it takes a lower amount of speed increase until drag equals the gravitational pull, and terminal velocity is reached.
- D-Coder 10y ago
  Thus, take a compressed-air tank with you. Point it down and open the valve to increase the air density that you are falling through. Is this so complicated???
  - harperlee 10y ago
    That basically amounts to a jetpack, and yes it would help!
- todd8 10y ago
  Yes. Assuming a relatively consistent body density, mass will be proportional to the cube of the linear dimension (say height of person falling) and cross-sectional area will be proportional to the square of the linear dimension. This is why an ant can make it to the ground without a parachute. F_drag = K_1 * velocity^2 * Size^2 F_gravity = K_2 * Size^3 Acceleration will be zero when the forces balance so terminal velocity is: v_term = sqrt((K_2 * Size^3)/(K_1 * Size^2)) = K*sqrt(Size) So if an ant is say 10mm long and a human is 2m long (200 * the length of the ant) the human falls 14 times faster. Furthermore, the forces on our bones at impact will be likely be proportional to the cube of our size while their strength will be proportional to their cross section, related to the square of our size. This give the ant a big advantage at impact as well. Finally, I would probably die of fright on the way down, the ant wouldn't know any better.
goodcanadian 10y ago
It is not solely about weight. It is the ratio between weight and surface area. Surface area tends to go as the square of the size whereas mass tends to go as the cube. For objects of the same density (all people are about the same), smaller and thus lighter ones have a greater surface area to mass ratio, and thus a lower terminal velocity.
- kqr 10y ago
  This is also why, e.g., ants basically never die when you drop them. Also helps cats.

Air resistance affects lighter stuff more, proportionally, and gives it a lower terminal velocity. A mouse can be dropped and survive (maybe with broken limbs) from almost any height, as there's not a lot of mass behind it and the air will keep it from going too fast. This is in contrast to the Galilean experiment where you drop two things and they fall at the same rate regardless of mass - this is true in a vacuum but not in atmosphere.

barrkel 10y ago
"Air resistance affects lighter stuff more" This is nonsense. Air resistance is caused by drag and has nothing to do with weight. An arrow will fall faster to the ground than big balloon, despite weighing the same.
- PhasmaFelis 10y ago
  It's awkwardly phrased, but it's pretty clear what they intended from the rest of the comment.
- Nursie 10y ago
  "This is nonsense. Air resistance is caused by drag and has nothing to do with weight. An arrow will fall faster to the ground than big balloon, despite weighing the same." But if you had two arrows of different weights, air resistance would act to slow the lighter one more. So no, it's not nonsense.

arnarbi 10y ago

Like a ping-pong ball vs a golf ball. The gravitational force is smaller on a light object, so less drag is required to counter it. Being the same shape, that drag is reached at a lower speed than for the heavy object.

barrkel 10y ago

Gravitational force is proportional to mass; in a vacuum, the only thing that stops heavier things from falling faster is the fact that acceleration due to applied force is inversely proportional to mass, so the mass cancels out. Drag is proportional to cross-sectional area and the square of the velocity; mass doesn't factor in. There are two main forces on the falling object, then: gravity pulling it down, and drag pushing it up. Terminal velocity is reached when both are equal. Lower mass means less gravity, but drag is unaffected. Thus it takes a lower amount of speed increase until drag equals the gravitational pull, and terminal velocity is reached.

D-Coder 10y ago
Thus, take a compressed-air tank with you. Point it down and open the valve to increase the air density that you are falling through. Is this so complicated???
- harperlee 10y ago
  That basically amounts to a jetpack, and yes it would help!
todd8 10y ago
Yes. Assuming a relatively consistent body density, mass will be proportional to the cube of the linear dimension (say height of person falling) and cross-sectional area will be proportional to the square of the linear dimension. This is why an ant can make it to the ground without a parachute. F_drag = K_1 * velocity^2 * Size^2 F_gravity = K_2 * Size^3 Acceleration will be zero when the forces balance so terminal velocity is: v_term = sqrt((K_2 * Size^3)/(K_1 * Size^2)) = K*sqrt(Size) So if an ant is say 10mm long and a human is 2m long (200 * the length of the ant) the human falls 14 times faster. Furthermore, the forces on our bones at impact will be likely be proportional to the cube of our size while their strength will be proportional to their cross section, related to the square of our size. This give the ant a big advantage at impact as well. Finally, I would probably die of fright on the way down, the ant wouldn't know any better.

goodcanadian 10y ago

It is not solely about weight. It is the ratio between weight and surface area. Surface area tends to go as the square of the size whereas mass tends to go as the cube. For objects of the same density (all people are about the same), smaller and thus lighter ones have a greater surface area to mass ratio, and thus a lower terminal velocity.

kqr 10y ago
This is also why, e.g., ants basically never die when you drop them. Also helps cats.