Physics Question Urgent
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If a flowerpot and pencil drops from the same height, will they reach the ground at the same time with the same speed? (Or if u have Physics Matters TEXTBOOK refer to pg 60)
Why is the answer yes?
I thought that in real life there is air resistance and this would oppose the motion of the two moving objects such that the flowerpot will drop first?
Also does air resistance depends on surface area or mass?
Let me illustrate two examples:
One, a human with a parachute will fall slower than a golf ball, even though it is far heavier. (larger surface area- fall slower/ more air resistance)
Second, an ant will fall slower than an elephant, as it is far lighter?? (elephant has larger surface area so it should have more air resistance and theoretically fall slower but in real life it falls faster) WHY?
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i thought in physics we learn to neglect the air resistance?
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air resistance, or rather, fluid resistance depends on velocity, surface area as well as viscousity of the fluid.
Anyway, for flowerpot and pencil, the reason why you state the same is because
1) The distance is usually to short to have any significant difference; velocity is still too small.
2) Their surface area (that part that is parallel to the velocity) doesn't have too great a difference anyway.For 2), for a great difference, just compare between a normal piece of paper and a crushed piece.
For the ant and elephant, how do you know which will fall faster?
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For the ant and elephant, how do you know which will fall faster?
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/newtlaws/efar.html
But oops is feather instead of ant sry
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very urgent question?
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Originally posted by Peoplethinkimsarcastic:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/newtlaws/efar.html
But oops is feather instead of ant sry
Didn't they answer it quite well?
So in conclusion, the elephant falls faster than the feather because it never reaches a terminal velocity; it continues to accelerate as it falls (accumulating more and more air resistance), approaching a terminal velocity yet never reaching it. On the other hand, the feather quickly reaches a terminal velocity. Not requiring much air resistance before it ceases its acceleration, the feather obtains the state of terminal velocity in an early stage of its fall. The small terminal velocity of the feather means that the remainder of its fall will occur with a small terminal velocity.
For this question
But what if there were no air resistance? If air resistance could somehow be eliminated (by conducting the experiment in a vacuum), then which object - the elephant or the feather - would strike the ground first?
If there was no acceleration, both will strike the ground at the same time.
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Okay so is the air resistance that ultimately matters?
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Originally posted by Peoplethinkimsarcastic:
Okay so is the air resistance that ultimately matters?
Ya, and as I said before, this depends on the factors that affect air resistance as well, or rather, fluid resistance depends on velocity, surface area as well as viscousity of the fluid.
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haven finished yet. If say there are 2 objects and both does not reach terminal velocity. Both should still fall at different times because one reaches terminal velocity faster than the other.
Ok i guess i am just stating lol.
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Actually by right both should reach ground at different times because the net acceleration acting would be different.
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Originally posted by 16/f/lonely:
Actually by right both should reach ground at different times because the net acceleration acting would be different.
net acceleration = gravity(acceleration) - air resistance (acceleration)
air resistance will increase over time, until net acceleration is zero.... this means terminal velocity.
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Originally posted by skythewood:
net acceleration = gravity(acceleration) - air resistance (acceleration)
air resistance will increase over time, until net acceleration is zero.... this means terminal velocity.
Wrong. You cannot calculate net acceleration like that.You must calculate the net force first.
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eerrr... ok.
since, F=ma
net force = gravity force - air resistance force
F = F(g) - F(a) , at this point sub in F=ma
ma = ma(gravity) - ma (air resistance) , at this point, take out mass.
net acceleration = gravity(acceleration) - air resistance (acceleration) -
Originally posted by skythewood:
eerrr... ok.
since, F=ma
net force = gravity force - air resistance force
F = F(g) - F(a) , at this point sub in F=ma
ma = ma(gravity) - ma (air resistance) , at this point, take out mass.
net acceleration = gravity(acceleration) - air resistance (acceleration)Don't be lazy! It'll cost you a lot in exams.
I learnt it hard then.
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Originally posted by 16/f/lonely:
Don't be lazy! It'll cost you a lot in exams.
I learnt it hard then.
i have the feeling you are just joking, so let's just stop here.
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Originally posted by skythewood:
i have the feeling you are just joking, so let's just stop here.
I'm not.I can't be when I got back my exam paper with the word: LAZY! big big on my paper.
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Originally posted by 16/f/lonely:
I'm not.I can't be when I got back my exam paper with the word: LAZY! big big on my paper.
than i suggest you post full working here is sgforums to counter.
cos i used that formulae in NUS all the time, so i can afford to be lazy...
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Hmm, im from combine, the easier explanation is that gravatational pull is at 10m/s. thus they should reach at the same time
and becos of the weight they contain diff amount of gravitational potential energy, so the force that they reach the ground will be larger.
im not very sure though
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Originally posted by skythewood:
than i suggest you post full working here is sgforums to counter.
cos i used that formulae in NUS all the time, so i can afford to be lazy...
Nothing wrong with that, I just prefer playing safe. -
Originally posted by 16/f/lonely:
Nothing wrong with that, I just prefer playing safe.don't be lazy
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Originally posted by skythewood:
don't be lazy
Sorry I'm lazy. -
Originally posted by MyPillowTalks:
Hmm, im from combine, the easier explanation is that gravatational pull is at 10m/s. thus they should reach at the same time
and becos of the weight they contain diff amount of gravitational potential energy, so the force that they reach the ground will be larger.
im not very sure though
potential energy is mgh. so bigger the mass, the higher the P.E. but nope, that's not the right... have to stick with the more complicated explanation -
Originally posted by 16/f/lonely:
Wrong. You cannot calculate net acceleration like that.You must calculate the net force first.
skythewood is right actually. You can add up like that because acceleration is a vector and the accelerations involved are just either up or down.
He's doing vector sum of acceleration, very much like vector sum of forces. Maybe your teacher mark you wrong because of some requirements of the question.