all objects fall at the same speed?

[esa]

ok, heres the thing.. ive been thinking about this for a LONG time now, and have gotten nowhere (not even my physics teacher can help me). what im wondering is about is this...

 

all objects fall at the same rate (earth's gravity) and they have tested this with a feather and an apple in a vacuum, both do fall at the exact same time. however, when it is not in a vacuum, say in air. it is the surface area that effects the rate of fall, NOT the mass at all (which is what it says in the books). i know that this is true, but keep thinking about "momentum". say if you had two balls totally the same size, so that surface area wouldn't be a factor. the only difference between the two balls is one has a lot more mass then the other. we all know that things that have more mass, have more momentum. one can see this with cars compared to semitrucks for example. newtons law states that for every action, there is an equal and opposite reaction, yes? so wouldn't the ball with more mass "push" more air molecules away, then the one with lesser mass? i mean if you think of it, when both balls hit the ground, the one with more mass makes a greater/deeper impact creator (travels overall further). can't the same happen with air molecules being the thing "impacted"? you can try the same thing with throwing a ping-pong ball compared to a heavier one of the same size, which one could one throw farther? i know that in rocketry, that a rocket with more mass is said to have less "air resistance", because of the more enitial momentum it has. meaning that if you had the space shuttle and a small model rocket go at the same speed and cut off there engines at the same time, the space shuttle will coast much farther then the model rocket. how bout a bullet of lead compared to one of plastic? the one out of lead will "penetrate" much more, but won't it also "penetrate" the air much more as well?

 

so what im thinking is that air resistance cant be the only factor, or maybe there is a "backfire" way of how air resistance works? how about water, maybe some comparasions?

 

i know that there must be some simple explanation, but i cant seem to find it please help explain

 

esa

[Xecuter]

oai a yu taaking in inglish?

[esa]

oai a yu taaking in inglish?

6870909[/snapback]

 

o, btw im from canada... i should of stated that first

i understand norwegian and can read and write it, but english is just so much easier! *sry*

 

reply in norwegian, i can read it fine..

 

esa

[ATWindsor]

I don't know what books you have, but that only the surface area impacts the rate of fall is wrong, for at least two reasons (I haven't had about air restiance in a long time, so I might be a bit rusty),

 

1. The air drag depends not only on the surface area, but also on the shape of the object.

 

2. The air drag (proportional to speed in low speeds and speed^2 in high speeds) is a force, the same force on a heavy object will have less impact, than the same force on a light object.

 

So in addition to the surface area, bot mass and shape affect the speed.

 

AtW

[esa]

o i meant shape! sry bout that, the shape of the object i meant**

 

but u say that the mass DOES have an affect on the rate at which it falls (in air for example??

 

esa

[ATWindsor]

o i meant shape! sry bout that, the shape of the object i meant**

 

but u say that the mass DOES have an affect on the rate at which it falls (in air for example??

 

esa

6871024[/snapback]

 

Yes, because the air drag is a force, and as you know (?) the force downward on a heavy object (mass*gravity) is larger then on a light one, so the same force upward (comming from the air drag), will impact the heavy object less than the light object.

 

AtW

[Xecuter]

oai a yu taaking in inglish?

6870909[/snapback]

 

o, btw im from canada... i should of stated that first

i understand norwegian and can read and write it, but english is just so much easier! *sry*

 

reply in norwegian, i can read it fine..

 

esa

6870931[/snapback]

 

Oh, cool! Anyways:

 

As i understand it, since the ball with more mass needs more energy to fall, it equals the air resistance. I read it today in Illustrert Vitenskap.

 

To make it more clear:

- A ball with little mass, penetrates the air with less force, but also needs less energy to fall.

- A ball with more mass, penetrates the air with greater force, but it also needs more enegry to fall.

 

Hope you understand.

[esa]

oh i see, so saying that it is JUST the shape of the object that decides how fast an object falls is wrong yes? (and then my thinking was right)

 

in the vacuum of space, there is no "force" like the air, so then they fall at the same rate, whatever size/shape (as tested with a feather and apple)...

 

why do the school books say its just the shape that decides the rate of fall an object has (falling in air)? ive always thought that there must be something else because of momentum, now i know

 

would it be easier to see if the air was replaced with water? any thoughts...

 

esa

[esa]

oai a yu taaking in inglish?

6870909[/snapback]

 

o, btw im from canada... i should of stated that first

i understand norwegian and can read and write it, but english is just so much easier! *sry*

 

reply in norwegian, i can read it fine..

 

esa

6870931[/snapback]

 

Oh, cool! Anyways:

 

As i understand it, since the ball with more mass needs more energy to fall, it equals the air resistance. I read it today in Illustrert Vitenskap.

 

To make it more clear:

- A ball with little mass, penetrates the air with less force, but also needs less energy to fall.

- A ball with more mass, penetrates the air with greater force, but it also needs more enegry to fall.

 

Hope you understand.

6871076[/snapback]

 

o ok, but i thought everything accelerated at the same time (9.81m/s^2, gravity)?

 

esa

[ATWindsor]

oh i see, so saying that it is JUST the shape of the object that decides how fast an object falls is wrong yes? (and then my thinking was right) 

 

in the vacuum of space, there is no "force" like the air, so then they fall at the same rate, whatever size/shape (as tested with a feather and apple)...

 

why do the school books say its just the shape that decides the rate of fall an object has (falling in air)? ive always thought that there must be something else because of momentum, now i know 

 

would it be easier to see if the air was replaced with water? any thoughts...

 

esa

6871113[/snapback]

 

Yes, that is wrong.

 

I don't know what school-books who says this, but my books does not say this, you should complain to your teacher and/or the author of the book. As it is not a good thing if the book gives wrong information.

 

AtW

[ATWindsor]

o ok, but i thought everything accelerated at the same time (9.81m/s^2, gravity)?

 

esa

6871123[/snapback]

 

That is correct, but the force exerted on the heavy object is larger (force= mass times acceleration)

 

AtW

[Xecuter]

oai a yu taaking in inglish?

6870909[/snapback]

 

o, btw im from canada... i should of stated that first

i understand norwegian and can read and write it, but english is just so much easier! *sry*

 

reply in norwegian, i can read it fine..

 

esa

6870931[/snapback]

 

Oh, cool! Anyways:

 

As i understand it, since the ball with more mass needs more energy to fall, it equals the air resistance. I read it today in Illustrert Vitenskap.

 

To make it more clear:

- A ball with little mass, penetrates the air with less force, but also needs less energy to fall.

- A ball with more mass, penetrates the air with greater force, but it also needs more enegry to fall.

 

Hope you understand.

6871076[/snapback]

 

o ok, but i thought everything accelerated at the same time (9.81m/s^2, gravity)?

 

esa

6871123[/snapback]

 

Hey, don't kill the messenger! I just read it, i might have misread it.

[esa]

wait wait wait, now im getting even more mixed up

 

does the mass cancel eachother out? like an object with little mass compared to one with lots, so they overall "fall" at the same rate/time?

 

esa

[esa]

u might of misread it? but what if u didnt, very strange...

 

so far i have to go with what ATWindsor is saying (so far*)

 

lol, but i think i need some documentation on "this" does anybody have any?

 

esa

[ATWindsor]

wait wait wait, now im getting even more mixed up 

 

does the mass cancel eachother out? like an object with little mass compared to one with lots, so they overall "fall" at the same rate/time?

 

esa

6871156[/snapback]

 

If you have to objects of same shape and size, the force upward on them will be the same at a given speed (the upwards force from the air dows not depend on the mass), but the heavier object will have more force downwards (the downward force from gravity depends on the mass). So the mass does not cancel eachouter out.

 

AtW

[gaardern]

For low velocity objects falling from rest:

v(t) = (mg*(1-e^(-bt/m)))/b

 

b=constant depending on the fluid and the dimensions of the object

 

Heavier objects fall faster...

Endret 15. september 2006 av gaardern

[ATWindsor]

u might of misread it? but what if u didnt, very strange...

 

so far i have to go with what ATWindsor is saying (so far*)

 

lol, but i think i need some documentation on "this"    does anybody have any?

 

esa

6871176[/snapback]

 

What kind of documentation do you need? Like a reference to a book or something?

 

AtW

[esa]

u might of misread it? but what if u didnt, very strange...

 

so far i have to go with what ATWindsor is saying (so far*)

 

lol, but i think i need some documentation on "this"    does anybody have any?

 

esa

6871176[/snapback]

 

What kind of documentation do you need? Like a reference to a book or something?

 

AtW

6871212[/snapback]

 

Yes! Because I have been argueing with my physics teacher (which I'm also teaching him a little about rocket science ;p) that there must be some other factor other then the shape of the object Can't wait to prove them wrong!

 

esa

[ATWindsor]

u might of misread it? but what if u didnt, very strange...

 

so far i have to go with what ATWindsor is saying (so far*)

 

lol, but i think i need some documentation on "this"    does anybody have any?

 

esa

6871176[/snapback]

 

What kind of documentation do you need? Like a reference to a book or something?

 

AtW

6871212[/snapback]

 

Yes! Because I have been argueing with my physics teacher (which I'm also teaching him a little about rocket science ;p) that there must be some other factor other then the shape of the object Can't wait to prove them wrong!

 

esa

6871246[/snapback]

 

In the book I have (Young & Freedman - University Physics 9th edition), this is documented in page 138 and 146

 

But i guess any book on the same level will have something about air drag.

 

AtW

Endret 15. september 2006 av ATWindsor

[gaardern]

Terminal velocity:

 

v(tv)=sqrt(2mg/pACd)

 

p=density

A=Reference area of object

Cd=drag coeffesient

 

Again, if the geometry of the objects is the same, the heavier one falls faster...

Endret 15. september 2006 av gaardern