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Tue 29 Sep, 2009 11:20 pm
When you drop a boewling ball and a marble off the side of an apartment building at the same time, Witch one will hit the ground first? Or, Will they hit at the same time?
Discounting possible effects of air resistance, they'd hit the earth at the same time (assuming they both hit at the same elevation--this doesn't hold true, for example, if one hit, say, the roof of a parked car while the other continued stright down to the ground, or if one bounced off the head (or sunk in, in the case of a bowling ball) of a passing pedestrian). Next question.
@jaimeeferguson,
Can't tell, without knowing the respective densities. If both had the same composition (they don't) the larger sphere would hit first as it would have less cross sectional density. The greater the distance, ceteris paribus, the further apart would be the landing.
@roger,
roger wrote:
Can't tell, without knowing the respective densities. If both had the same composition (they don't) the larger sphere would hit first as it would have less cross sectional density. The greater the distance, ceteris paribus, the further apart would be the landing.
This is false. Ignoring air resistance, they would strike the ground simultaneously regardless of weight or density.
@Brandon9000,
But Roger was not ignoring air resistance.
Weight increases as the cube of the radius. Cross-sectional area increases as the square of the radius.
@DrewDad,
DrewDad wrote:
But Roger was not ignoring air resistance.
Weight increases as the cube of the radius. Cross-sectional area increases as the square of the radius.
It's very hard to tell what he meant. There is no mention of air resistance in his post. If he intended to include all forces, then I withdraw my comment. I'd be interested to know whether the effect of air resistance is appreciable for a typical bowling ball and marble falling, say, 30 - 100 ft.
@Brandon9000,
Air resistance was not mentioned because air resistance was not ignored. The OP was dropping stuff from an apartment building. Not many apartment buildings on the moon, are there?
Frankly, my intuitive feeling is that for objects of the size and density mentioned and typical heights for apartment buildings (say under 100 ft), air resistance is not appreciable .
@Brandon9000,
Ignoring wind resistance, then an object falling from 100 feet would be traveling at nearly 55 miles per hour at the time of impact.
I would say that's easily fast enough for one to need to take wind resistance into account.
@DrewDad,
On a bicycle, it gets very important somewhere around 15 mph. Not suggesting I resemble a bowling ball, or anything.
@MontereyJack,
Then there's the possible question on how fast can one run away before being caught by the inevitable 911 phone call and police chase.
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