Rate of Speed?

[Untergang]

Ok, so my friend and I were arguing whether or not all object, in the same shape, will fall at the same speed and he says they will, but I don't think so. Wouldn't the density of the object have a huge impact on the velocity of the object aswell as the acceleration rate? (the argument was between a square block of led and a square block of feathers.

[Tormod]

Your view is the Aristotelian view. Galileo Galilei proved that objects *regardless of weight* fall at the same rate *except* for air friction. The density has nothing to do with the speed if the objects fall in vacuum.

 

However, on Earth a feather will fall slower than a rock because the feather is obstructed by the atmosphere. If you pack each of the items into two equal plastic bags then the problem more or less disappears (there will still be measureable friction for the lighter bag).

 

(BTW what is a square block of feathers?)

[Qfwfq]

Cubic, I guess.

 

He must be reasoning on the terminal velocity.

[Untergang]

By a block of feathers I was just trying to exagerate that they were the same shape but different density.

[Greg_G47]

well, we could be really picky and say you're right and that heavier objects do fall faster.

 

f = Gm1m2/r^2 so the total acceleration due to gravity of two objects falling towards each other is equal to (Gm1m2/r^2)/m1 + (Gm1m2/r^2)/m2 or (Gm1+Gm2)/r^2

 

You wouldn't notice that difference though unless you were dropping say... the moon and a baseball. Most of the time we assume that m1 is the mass of earth and m2 is the mass of the falling object, Gm2 is comparatively very small so we ignore it. This means we're left with G times the mass of earth divided by the radius of earth squared (since we're usually not too far off the surface) and that gives the acceleration of ~9.81m/s^2 which works for most "reasonable" objects.

 

Of course there's still wind resistance. The faster you go the stronger it gets until the acceleration due to gravity equals the acceleration (in the opposite direction) due to banging into air molecules. At this point the speed of the object stays constant as long as atmospheric conditions do. This is called terminal velocity and it varies depending on the shape, size and mass of the object. different or larger shapes/sizes bang into more air creating more air resistance, causing them to fall slower than other objects of similar mass (parachute versus 30lb dumbell), and heavier objects of similar size create more downward force with the same acceleration (f=ma) thus they may fall faster (parachute versus elephant).

 

And that's just about everything I can think to tell you about dropping things. Hope it helps.