Can someone explain this sciencey stuff!

Potential-Monke

OK, just had an argument with a colleague, and we're both convinced we're right. It's in relation to falling objects. Neither of us have studied this, but we're both going on what we think is right.

I know the experiment of dropping a feather and bowling ball in a vacuum and they both hit the ground at the same time. But outside of a vacuum, ie: here on Earth, the bowling ball will hit the ground first, because wind resistance and weight.

So I'm 12.5 stone, he's 11. He thinks that if we both jumped off from 200ft, we hit the ground at the same time. In space, yes, he's right, but on Earth, I believe I'm right in thinking that i'll hit the ground before him. Same with a bowling ball and tennis ball. From high enough, the bowling ball will hit the ground first as it has a higher terminal velocity is my understanding. He thinks they'll hit at the same time.

Who's right? I Googled, and i'm even more confused. I don't understand the scientific explanations, with numbers and letters denoting stuff, so in simple English, who's right?

On a side note, I really wish Sciene was a thing when I was in school.

Wesser

You are right

snowcat

If you both do a synchronized swan dive you will both hit the ground at nearly the exact same time. Weight does not make a difference just your Coefficient of drag.

abbir

Ignore me, I don't know what I was thinking when I wrote that

raspberrypi67

abbir wrote: »

Your weight doesn't matter. It is not the difference in weight of a feather and bowling ball on earth, it is only the wind resistance.

Terminal velocity occurs when the air resistance (sometimes called "drag") force equals the weight of the falling object. This means that: the object is falling with a constant velocity - its acceleration is zero. heavy objects will have a higher terminal velocity than light objects.

Auguste Comte

When people are skydiving fat lads fall quicker than skinny lads and use different body positions and jump suits to even things out. Not much difference over a couple of hundred feet though but the principle is the same.

CinemaGuy45

Get your friend to drop the two out of a window you need to be right under on the ground to gauge the speed.

zuutroy

Mass has nothing to do with it either in idealised vacuum free fall or in the real world. The difference in drag force for two falling bodies is determined by the cross sectional area perpendicular to the direction of motion, so the only reason the heavier person would fall faster is that they were wider. If you took a small person and a tall person with the same cross sectional area (waist size for argument's) sake and they both jumped feet first off a building, they would accelerate at the same rate regardless of the fact that the tall person is heavier. This all assumes you aren't falling far enough to reach terminal velocity which would be valid for a jump from 200ft.

Akrasia

Mass does come into it. Heavy objects have more mass, and therefore gravity has a stronger affect on more massive objects, however, larger objects also have more inertia, so it takes more force to cause a heavy object to move compared with a light object.

In an atmosphere the reason why light objects don't fall as fast is because their velocity is being constantly changed by buffeting from the atmosphere as the gasses get in the way, while a heavy object takes more force to change it's velocity, so the relatively small atmospheric pertubations don't have as much of an effect on it's velocity.

zuutroy

I'm only a physics professor, what would I know?! ¯\_(ツ)_/¯

biko

Somewhat related

https://www.youtube.com/watch?v=-fC2oke5MFg

fly_agaric

Akrasia wrote: »

Mass does come into it. Heavy objects have more mass, and therefore gravity has a stronger affect on more massive objects.

When it is planet earth (solid rock ball, diameter 13000 km or something) and 2 fellows that differ by a few 10s of kgs in mass any difference in force is negligible. Can assume acceleration due to gravity on them is the same.

edit:...apologies, acceleration is same regardless of the mass, but force is bigger as I think you were saying (...going back to bed now)

Akrasia

zuutroy wrote: »

I'm only a physics professor, what would I know?! ¯\_(ツ)_/¯

Pffft, you can prove anything with facts

Akrasia

fly_agaric wrote: »

When it is planet earth (solid rock ball, diameter 13000 km or something) and 2 fellows that differ by a few 10s of kgs in mass any difference in force is negligible. Can assume acceleration due to gravity on them is the same.

That's true, but the Mass does affect the inertia of the body which is why heavy objects can go through more resistance. That's all I was saying

kneemos

Akrasia wrote: »

That's true, but the Mass does affect the inertia of the body which is why heavy objects can go through more resistance. That's all I was saying

Depends on the shape of the object surely?

Pedro K

zuutroy wrote: »

Mass has nothing to do with it either in idealised vacuum free fall or in the real world. The difference in drag force for two falling bodies is determined by the cross sectional area perpendicular to the direction of motion, so the only reason the heavier person would fall faster is that they were wider. If you took a small person and a tall person with the same cross sectional area (waist size for argument's) sake and they both jumped feet first off a building, they would accelerate at the same rate regardless of the fact that the tall person is heavier. This all assumes you aren't falling far enough to reach terminal velocity which would be valid for a jump from 200ft.

I'm curious about this. I'm not, by any means, up on my fluid dynamics. The wiki for terminal velocity says Vt=sqrt(2mg/[rho]AC)

Why is m in the equation if mass has nothing to do with it?

(This isn't an "aha, I got you" attempt, by any means. You've said you're a physics professor, and I'm genuinely curious.)

Leroy Brown

kneemos wrote: »

Depends on the shape of the object surely?

Falling style too.

Potential-Monke wrote: »

So I'm 12.5 stone, he's 11. He thinks that if we both jumped off from 200ft, we hit the ground at the same time. In space, yes, he's right, but on Earth, I believe I'm right in thinking that i'll hit the ground before him.

Who's right?

In theory yes, you are heavier so you hit the ground faster, as professor said already

F = mg (F - speed, m - mass of your body, g = 9.81 m/s2 Earth's gravity)

F1= 12.5 x 9.81
F2 = 11 x 9.81

F1 > F2, but it is in case if you both are same shape and it is free falling (not jumping) because moving your bodies in different ways you can play on air resistance - "falling with style" like in this video

https://www.youtube.com/watch?v=XDZiGVdZG08

the beer revolu

Bowling ball and beach ball of same diameter.

I'm pretty sure the bowling ball will hit the ground sooner. Mass, surely must be a factor in the real world?

Wabbit Ears

uptherebels

the beer revolu wrote: »

Bowling ball and beach ball of same diameter.

I'm pretty sure the bowling ball will hit the ground sooner. Mass, surely must be a factor in the real world?

But if you dropped both off a building the beach ball wouldn't follow the same path as the bowling ball due to wind etc. Drag/ air density would also affect the shape of the beach ball affecting cross sectional area. This is why the feather example is in a vacuum so the only force acting is gravity.

mcmoustache

the beer revolu wrote: »

Bowling ball and beach ball of same diameter.

I'm pretty sure the bowling ball will hit the ground sooner. Mass, surely must be a factor in the real world?

Imagine a bowling ball and a hypothetical empty ball of the same shape and hardness that weighs 1 gram.

If you fill the ball with helium, it won't even drop so yes, mass comes into play but it does so because of the mass of the air and its resistance.

In a vacuum, the bowling ball and identically shaped helium ball would both fall at the same rate.

If the ball was filled with air so that it weighed 1 gram the ball would now fall in the air but it would do so more slowly than the bowling ball. This is because the bowling ball's mass is greater and therefore better at countering the air resistance. It's the same as what happens when you throw a balloon filled with air versus one filled with urine. The mass of the píss balloon means that it has a higher momentum than the air balloon and it requires more force to change that momentum.

sbsquarepants

raspberrypi67 wrote: »

Terminal velocity occurs when the air resistance (sometimes called "drag") force equals the weight of the falling object. This means that: the object is falling with a constant velocity - its acceleration is zero. heavy objects will have a higher terminal velocity than light objects.

True, but in reality it's all down to drag.
If you doubt that, would you rather jump out of a plane butt naked weighing 12 stone, or fully dressed and wearing a parachute and weighing 14?

kneemos

the beer revolu wrote: »

Bowling ball and beach ball of same diameter.

I'm pretty sure the bowling ball will hit the ground sooner. Mass, surely must be a factor in the real world?

If you deflated the beach ball and scrunched it up into a tight lump both would probably hit the ground not far apart.

Potential-Monke

Ok, so in my example, 200ft is not high enough to make a difference, but if we both jumped from 2000ft, I should hit the ground first? Stupid physics!