# Free fall - AS PhysicsWatch

#1
If two objects of exact same surface area/shape, but of different masses are dropped on the Earth, which one hits the ground first? I was under the impression they would hit the floor at the same time, however in the physics textbook it says that the air resistance on the one with lower mass has a greater effect on it due to its lower weight.

Would be awesome if anyone has any input on this, thanks!
0

4 years ago
#2
(Original post by Cipherhythm)
If two objects of exact same surface area/shape, but of different masses are dropped on the Earth, which one hits the ground first? I was under the impression they would hit the floor at the same time, however in the physics textbook it says that the air resistance on the one with lower mass has a greater effect on it due to its lower weight.

Would be awesome if anyone has any input on this, thanks!
I'm not 100% sure but here's my input. An object's weight is directly proportional to its mass. The drag force depends on a number of things but not on weight. Therefore, the drag force on two objects with the same surface area and shape travelling at the same velocity would be equal. The acceleration due to gravity is constant but as a=F/m, the decelerative effect of the drag would be greater for the lighter object than for the heavier object. So for the same velocity, my guess is that the heavier object would be accelerating at a slightly greater rate. I'm not sure how this would work out in the end though because the velocities are all dynamic. Also, the terminal velocities of the two objects will be the same. So even if there is a difference, it will be pretty small.
1
4 years ago
#3
Hey,

As far as I am aware air resistance is not dependant on mass, but more on shape etc (as we see with the classic feather and bowling ball question). Theoretically they will hit the ground at the exact same time, this is because the acceleration due to gravity (9.81 m/s^2) is the same for all objects, it's the force (weight) that changes with mass as F=mg. If they are the exact same shape and surface area I see no reason for the object with less mass to hit the floor first. However, if it's the textbook that has stated this I would show the specific section to your teacher who can probably clear things up a little bit more than I can because maybe it's just a context issue as opposed to a theoretical lack of understanding?

Hope that helps,

Emily
1
#4
Hey guys,

Agh, it's pretty complicated after you consider the relativistic effects, for example, from the heavier objects perspective, it exerts a higher force on the Earth than the lighter one, etc.

My teacher said something along the lines of, the upward air resistance has a greater effect on the object with lower mass due to its lower weight, but to me something still doesn't add up right.

Thanks for the input guys, keep it coming
0
4 years ago
#5
(Original post by Cipherhythm)
Hey guys,

Agh, it's pretty complicated after you consider the relativistic effects, for example, from the heavier objects perspective, it exerts a higher force on the Earth than the lighter one, etc.

My teacher said something along the lines of, the upward air resistance has a greater effect on the object with lower mass due to its lower weight, but to me something still doesn't add up right.

Thanks for the input guys, keep it coming
It's nothing to do with gravity, heavier objects experience a greater gravitational force but they also have a greater mass so the acceleration is constant. The air resistance explanation makes sense but again, the effect would be minute.
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