Acceleration of a free falling object?

[Bluedog]

G'day, this probably seems like a strange question to be asking here, but some of you guys seem to be pretty clued up in the way of things, and maybe you could explain something to me.
High school physics stuff really, infact I can even remember my year 11 physics teacher talking about this, but I was way more interested in the girl in the seat beside me and the football game on the oval out the window, than I was in the grey haired old fart droning monotonous crap up the front.

What is the rate of acceleration of a free falling object?
Is it 2m per sec/sec? or does it's velocity double every second? or am I WAY off, and it is something else entirely?.

Also, to my understanding, given that both objects have the same aerodynamic shape, same size etc, but one being heavier ( basically all factors being equal bar weight), two objects released simultaniously from exactly the same height, will hit the earth at exactly the same time regardless that one object is heavier, but with very differant kinetic energy states....ie the heavier object will take more force to halt it's motion than the lighter object, or another way to put it, the heavier object's impact force would be greater.
Am I correct at all in this? could someone explain if I am wrong please.


He he... I was bored after lunch at work today, so I strolled out the back, sparked up a joint, then went and hassled the big angry bikie bloke in the machine shop next door, we went from talking about the show he saw on telly last night about what caused the dinosaurs to all die out, to him telling me that no way a meteor hitting earth could have done it, to me arguing that a meteor is screaming right along, to atmosphere re-entry angles for space craft, the future of air travel and the velocity of free falling objects......or something like that, the J makes it all a bit blurry now ;-)
Anyway, he flat disagrees about the two objects of differing weights falling/accelerating at the same rate, and I would REALLY like to prove him wrong.
Can anyone set me straight?

Thanks
Blue

[Creamo]

This is off the top off my head-

The motion of a free falling object can be described by Newton's second law of motion, force (F) = mass (m) times acceleration (a). We can do a little algebra and solve for the acceleration of the object in terms of the net external force and the mass of the object ( a = F / m). The net external force is just the weight of the object (F = W). Substituting into the second law equation gives: a = W / m = m * g / m = g . The acceleration (change of velocity) of the object then becomes the gravitational acceleration. The mass, size, and shape of the object are not a factor in describing the motion of the object. So all objects, regardless of size or shape or mass (or weight) will free fall at the same rate; a beach ball will fall at the same rate as an airliner. Knowing the acceleration, we can predict the velocity and location of a free falling object at any time. If the object were falling through the atmosphere, there would be an additional drag force acting on the object. And the physics involved with describing the motion of the object would be more complex. Or I might have copied it off a webpage.

[funkedup]

Not bad Creamo.  We might let you work on airplanes eventually!

FYI g is 9.80665 meters/sec/sec or 32.17 feet/sec/sec

There is a fancier law of gravity for the more general case but what Creamo posted works great for vehicles and other objects on earth or in the atmosphere.

[Bluedog]

OK Creamo....now I'm REALLY confused......
Why I said about the aerodynamic shape etc, is this....you cant tell me that say a feather, is going to free fall at the same rate as say a shot put.....the feather is going to "slide' from side to side, and tumble as it falls, whereas the shot is going to fall stright down??

[funkedup]

In a vacuum (no air) they fall at the same rate.  When aerodynamic or other non-gravitational forces act on them then they can fall at different rates.

[Creamo]

I believe that formula shows from a vaccum standpoint, then adds that aerodynamic forces ala drag comes into play. Dunno, ask funked.

[funkedup]

Creamo's right.  All the drag and other junk goes into the F term, which makes the feather fall slower than the shot.

[Bluedog]

So say you climb to the top of the Statue of Liberty with two  spheres 10 cm in diameter, one made of carbon fiber, and weighing bugger all, and the other of lead and weighing quite a bit, and drop them at exactly the same time, will theyaccelerate , and impact at the same rate/time? or not.
Aerodynamically identical shapes, so drag/air resistance would be the same for both, should factor out the question of vacuum or air shouldnt it?

[LtHans]

No, they won't.  Air drag relys on
thrust versus surface area and surface texture.  Thrust in this case is provided by nature called gravity which is  9.8 ms^2 to be precise.

Now, if you had two spheres both perportional to each other, then they would hit at the same time.  A demostration I've seen is a bowling ball and a golf ball.

[Pyton]

So say you climb to the top of the Statue of Liberty with two spheres 10 cm in diameter, one made of carbon fiber, and weighing bugger all, and the other of lead and weighing quite a bit, and drop them at exactly the same time, will theyaccelerate , and impact at the same rate/time? or not.

Not, they are not aerodynamically identical. To get aerodynamically identical objects they must have the same drag/mass. If the spheres were same size and shape they would have the same drag but different mass. To get them aerodynamically identical you would have to reduce the drag of lighter object (or increase the drag of bigger object).

[Bluedog]

Thanks guys.

[Otto]

"There's no Force of Gravity, the Earth just sucks"

[Elfenwolf]

Originally posted by Bluedog
So say you climb to the top of the Statue of Liberty with two  spheres 10 cm in diameter, one made of carbon fiber, and weighing bugger all, and the other of lead and weighing quite a bit, and drop them at exactly the same time, will theyaccelerate , and impact at the same rate/time? or not.
Aerodynamically identical shapes, so drag/air resistance would be the same for both, should factor out the question of vacuum or air shouldnt it?

If you climb to the top of the Statue of Liberty and start throwing toejam you'll get your bellybutton shot as a terrorist. Get out of the sun, Bluedog. You're talking crazy.

[2Slow]

Originally posted by funkedup
In a vacuum (no air) they fall at the same rate.  When aerodynamic or other non-gravitational forces act on them then they can fall at different rates.

This was demonstrated during one of the moon landing.

[Mr Hanky]

Originally posted by 2Slow


This was demonstrated during one of the moon landing.

Quite correct.  They dropped a hammer and a feather while on the moon... both hit at the same time.