If you drop objects that weigh different amounts, which will hit the ground first? What you need:
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What happens Gravity is the force that causes things to fall to earth. When you drop a ball (or anything) it falls down. Gravity causes everything to fall at the same speed. This is why balls that weigh different amounts hit the ground at the same time. Gravity is the force acting in a downwards direction, but air resistance acts in an upwards direction. The flat piece of paper takes much longer to hit the ground, not because it is lighter, but because it has a larger surface area so it gets caught up by air resistance. When it is scrunched into a ball shape, it should hit the ground at about the same time as a ball, and hit the ground earlier than a flat piece of paper, even though they both weigh the same. Back to Home Science activities.
QUESTION #6 Asked by: Terri If no air resistance is present, the rate of descent depends only on how far the object has fallen, no matter how heavy the object is. This means that two objects will reach the ground at the same time if they are dropped simultaneously from the same height. This statement follows from the law of conservation of energy and has been demonstrated experimentally by dropping a feather and a lead ball in an airless tube. When air resistance plays a role, the shape of the object becomes important. In air, a feather and a ball do not fall at the same rate. In the case of a pen and a bowling ball air resistance is small compared to the force a gravity that pulls them to the ground. Therefore, if you drop a pen and a bowling ball you could probably not tell which of the two reached the ground first unless you dropped them from a very very high tower. Answered by: Dr. Michael Ewart, Researcher at the University of Southern California The above answer is perfectly correct, but, this is a question that confuses many people, and they are hardly satisfied by us self-assured physcists' answers. There is one good explanation which makes everybody content -- which does not belong to me, but to some famous scientist but I can't remember whom (Galileo?); and I think it would be good to have it up here. (The argument has nothing to do with air resistance, it is assumed to be absent. The answer by Dr. Michael Ewart answers that part already.) The argument goes as follows: Assume we have a 10kg ball and a 1kg ball. Let us assume the 10kg ball falls faster than the 1kg ball, since it is heavier. Now, lets tie the two balls together. What will happen then? Will the combined object fall slower, since the 1kg ball will hold back the 10kg ball? Or will the combination fall faster, since it is now an 11kg object? Since both can't happen, the only possibility is that they were falling at the same rate in the first place. Sounds extremely convincing. But, I think there is a slight fallacy in the argument. It mentions nothing about the nature of the force involved, so it looks like it should work with any kind of force! However, it is not quite true. If we lived on a world where the 'falling' was due to electrical forces, and objects had masses and permanent charges, things would be different. Things with zero charge would not fall no matter what their mass is. In fact, the falling rate would be proportional to q/m, where q is the charge and m is the mass. When you tie two objects, 1 and 2, with charges q1, q2, and m1, m2, the combined object will fall at a rate (q1+q2)/(m1+m2). Assuming q1/m1 < q2/m2, or object 2 falls faster than object one, the combined object will fall at an intermediate rate (this can be shown easily). But, there is another point. The 'weight' of an object is the force acting on it. That is just proportional to q, the charge. Since what matters for the falling rate is q/m, the weight will have no definite relation to rate of fall. In fact, you could have a zero-mass object with charge q, which will fall infinitely fast, or an infinite-mass object with charge q, which will not fall at all, but they will 'weigh' the same! So, in fact, the original argument should be reduced to the following statement, which is more accurate: If all objects which have equal weight fall at the same rate, then _all_ objects will fall at the same rate, regardless of their weight.In mathematical terms, this is equivalent to saying that if q1=q2 then m1=m2 or, q/m is the same for all objects, they will all fall at the same rate! All in all, this is pretty hollow an argument. Going back to the case of gravity.. The gravitational force is
 ( G is a constant, called constant of gravitation, M is the mass of the attracting body (here, earth), and m1 is the 'gravitational mass' of the object.) And newton's law of motion is
where m2 is the 'inertial mass' of the object, and a is the acceleration. Now, solving for acceleration, we find:
Which is proportional to m1/m2, i.e. the gravitational mass divided by the inertial mass. This is our old 'q/m' from the electrical case! Now, if and only if m1/m2 is a constant for all objects, (this constant can be absorbed into G, so the question can be reduced to m1=m2 for all objects) they will all fall at the same rate. If this ratio varies, then we will have no definite relation between rate of fall, and weight. So, all in all, we are back to square one. Which is just canceling the masses in the equations, thus showing that they must fall at the same rate. The equality of the two masses is a necessity for general relativity, and enters it naturally. Also, the two masses have been found to be equal to extremely good precision experimentally. The correct answer to the question 'why objects with different masses fall at the same rate?' is, 'beacuse the gravitational and inertial masses are equal for all objects.' Then, why does the argument sound so convincing? Since our daily experience and intuition dictates that things which weigh the same, fall at the same rate. Once we assume that, we have implicitly already assumed that the gravitational mass is equal to the inertial mass. (Wow, what things we do without noticing!). The rest of the argument follows easily and naturally...Answered by: Yasar Safkan, Physics Ph.D. Candidate, M.I.T.
I have seen youtube videos where two balls of the same size and of different masses are dropped from the same height and they hit the ground at the same time. I understand why this is so: the increase in the mass of a body increases the force of gravity acting on the body, but also decreases the body's willingess to move.
It makes sense to me in vacumm, but it somehow collides with what i have found written in my textbook. It goes more less like this: If you dropped an ant from a certain height in the air, it would not die upon landing, because the increase in speed as it is falling entails the increase of air resistance acting on the ant. The force of air resistance quickly balances the force of gravity acting on the ant. Up to this point the ant hasn't gained much speed and now is no longer accelerating. The speed is too little to cause it much harm when landing. Then it says that if you dropped a human from that height it would also stop accelerating at some point (at the point of air resistance balancing the body's weight), but it would happen much later. Therefore a human would gain more speed before landing and would die. This brings me back to the experiment with two balls.
Why doesn't the same principle work here?
I know their shape makes air resistance less powerful but it must still be there.
The lighter ball has lesser weight, so it should take less time for air resistance to counter the ball's weight than it should take in the case of the ball with greater mass.
The heavier ball should accelerate longer then the lighter ball, and therefore it should hit the ground first.
Please tell me, where is the error in my thinking. Answers and Replies
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anorlunda
You are correct, there. Is some air resistance, even for balls. It might be clearer for you if you imagine the metal in the smaller ball being hammered into the shape of a feather. With the bigger surface area, an iron feather will experience even more air resistance. Likes hipokrytus
BvU
No error, you are absolutely right: the experiment is to be conducted in vacuum to eliminate the influence of air resistance.
I'm not sure your argument
Likes hipokrytus
Thank you for your responses.
The experiment was conducted in the open air, and the performer lifted the balls as high as his hands could go up (so not very high).
So is it correct to conclude that at this height both balls were accelerating all the way?
And if the height were (much) greater we would notice difference in time in which they hit the ground?
sophiecentaur
It isn't really a matter of time. The fact is that the air resistance does not depend on the actual masses of two objects of the same size and shape. But the weight force is, of course, greater for the more massive object. (Just putting it a different way, anorlunda) Likes hipokrytus
I think i phrased that badly.
What I said there refers to the fact that air resistance increases if the velocity of a falling body icreases too.
And when this force of air resistance reaches a point where it balances the weight force of the body, the acceleration ceases, and the body is from then on falling with constant speed.
The time during which the ball with lesser weight is accelerating is shorter when compared to the time during which the heavier ball is accelerating because there is less weight force for the air resistance to balance (in the case of the lighter ball). Is that correct?
I may have phrased it even worse now.
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2) The complex behaviour of objects of various sizes and shapes within the atmosphere, which includes thermals and air currents as well as air resistance and the aerodynamic principles by which birds, aircraft and helicopters can fly. Likes hipokrytus
anorlunda
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Therefore, the time to reach terminal velocity is harder to define. It couild be infinite.
d) You'll hit the ground sooner or later.
anorlunda
d) You'll hit the ground sooner or later.
EDIT: I take all that back. PeroK is pointing out that terminal velocity could decrease with altitude because of air pressure, then approach will not by asymtotic. Likes hipokrytus
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When you drop two balls of different weights from the same height?
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