Weight And Falls

[JMJones0424]

the object with the biggest mass will touch the ground for about 10^-12 faster :)

You forgot to add + or -.  I don't doubt your claim, assuming it was a joke, but in all seriousness, do you know of any actual high precision tests that have been performed that could be useful to refer to in discussions like we are having here?  It is not necessarily obvious to those without a physics education that all objects regardless of mass fall at the same rate if you remove all effects other than gravity.  Proof by contradiction is how I accepted this to be the case, but I am a moron and my schooling was inadequate.  It would be useful to be able to point to specific measurements made.

Edited April 25, 2018 by JMJones0424

[EinsteinIsUseless199]

no

 

seconds lol   

[EinsteinIsUseless199]

ok but take a look at this article:http://www.physicsclassroom.com/class/circles/Lesson-3/Newton-s-Law-of-Universal-Gravitation

 

 

 

 

if you set mass1 to the object's mass and mass2 to the earth's mass , mass2 is being accelerated beacause of the force F that it is applying to mass2

Edited April 26, 2018 by EinsteinIsUseless199

[Moronium]

A lot of people here are saying the same thing in different ways, so I'll go ahead and throw in my two bits worth, Hazel, in the hopes it might help. By the same token, it might just create more confusion for you, but I'll try to put it in terms that go beyond the mere application of a formula.

 

1.  If you hit a golf ball with a baseball bat, it will go a lot farther than a bowling ball would if you hit it with the same force. Based on that thought, it would seem natural to conclude that a bowling ball would fall slower when subjected to the same force (gravity).   But, the assumption of the "same force" is the key here.  Although the word "gravity" is the same in each case, the amount of force gravity exerts on objects of different masses is NOT the same.

 

2.  According to Newton's law, gravity does not exert itself on all objects with the "same force," which, at first blush, sounds kind of mysterious.  It kinda sounds like some "conspiracy of nature" designed to fool and mislead us.  The force of gravity is proportional to the respective masses of the objects involved.  The more massive an object is, the more "force" the earth's gravity will apply to it.

 

3.  The term "mass" really just boils down to meaning "resistance to acceleration," aka "inertia." Since a more massive object is more resistant to acceleration, it follows that gravity must exert more force on it than on a less massive object if both are going to fall at the same rate.

 

4.  Newton never did try to explain "why" this is the case.  His universal law of gravitational attraction is just that--a mere law, and not a "theory of gravity."

 

Newton expressly said:

 

"It is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter without mutual contact...That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it."

 

 

 

Newton did not pretend to explain "how" gravity works.  He merely reduced his observations (and mathematical deductions therefrom) to a formula which is accurate.  If he didn't understand it, Hazel, then why should you?

 

To sum up, we know from observation that objects with different masses DO, in fact, fall at the same rate.  "Why" this should be the case is unknown.  But knowing that it is, in fact, the case, we can devise various concepts (such as mass, acceleration, force, etc.) to "explain" it.

 

Long before Pythagoras ever came up with his famous theorem (A squared plus B squared = C squared in a right triangle), people knew it was true in practice.  Ancient Egyptians used this knowledge in construction (Pyramids, etc.) to produce "right angles."

Edited April 26, 2018 by Moronium

[hazelm]

A lot of people here are saying the same thing in different ways, so I'll go ahead and throw in my two bits worth, Hazel, in the hopes it might help. By the same token, it might just create more confusion for you, but I'll try to put it in terms that go beyond the mere application of a formula.

 

1.  If you hit a golf ball with a baseball bat, it will go a lot farther than a bowling ball would if you hit it with the same force. Based on that thought, it would seem natural to conclude that a bowling ball would fall slower when subjected to the same force (gravity).   But, the assumption of the "same force" is the key here.  Although the word "gravity" is the same in each case, the amount of force gravity exerts on objects of different masses is NOT the same.

 

2.  According to Newton's law, gravity does not exert itself on all objects with the "same force," which, at first blush, sounds kind of mysterious.  It kinda sounds like some "conspiracy of nature" designed to fool and mislead us.  The force of gravity is proportional to the respective masses of the objects involved.  The more massive an object is, the more "force" the earth's gravity will apply to it.

 

3.  The term "mass" really just boils down to meaning "resistance to acceleration," aka "inertia." Since a more massive object is more resistant to acceleration, it follows that gravity must exert more force on it than on a less massive object if both are going to fall at the same rate.

 

4.  Newton never did try to explain "why" this is the case.  His universal law of gravitational attraction is just that--a mere law, and not a "theory of gravity."

 

Newton expressly said:

 

 

 

Newton did not pretend to explain "how" gravity works.  He merely reduced his observations (and mathematical deductions therefrom) to a formula which is accurate.  If he didn't understand it, Hazel, then why should you?

 

To sum up, we know from observation that objects with different masses DO, in fact, fall at the same rate.  "Why" this should be the case is unknown.  But knowing that it is, in fact, the case, we can devise various concepts (such as mass, acceleration, force, etc.) to "explain" it.

 

Long before Pythagoras ever came up with his famous theorem (A squared plus B squared = C squared in a right triangle), people knew it was true in practice.  Ancient Egyptians used this knowledge in construction (Pyramids, etc.) to produce "right angles."

This is definitely not my day.  Google did some resetting and I was unregistered.  Took a while to figure that out.  Anyway,   there have been a few clarifications from the three of you that I want to address but it will have to be later.  For now, just one question to moronium.  Wouldn't gravity exert less force on a falling ball than on an arced ball, the former expending some of its own energy in "free fall" and the later using only gravity's force?

 

"  If he didn't understand it, Hazel, then why should you?"  Right

[Moronium]

This is definitely not my day.  Google did some resetting and I was unregistered.  Took a while to figure that out.  Anyway,   there have been a few clarifications from the three of you that I want to address but it will have to be later.  For now, just one question to moronium.  Wouldn't gravity exert less force on a falling ball than on an arced ball, the former expending some of its own energy in "free fall" and the later using only gravity's force?

 

"  If he didn't understand it, Hazel, then why should you?"  Right

  Not sure I understand your question, Hazel, but I think this example may respond to it.

 

Suppose I have two bullets.  One of them is in a rifle which I am holding at shoulder height and which I have aimed in a line that is perfectly perpendicular to the ground.

 

The other bullet is right outside the rifle chamber.

 

Now, if I fire the rifle and drop the bullet next to it at the same time, then they will hit the ground at the same time (more or less, i.e., if you ignore the curvature of the earth and other factors which might have an infinitesimal effect).

 

The bullet fired from the rifle may not hit the ground until it's a mile away from me, but the "time" it hits will be known to me if I just watch the bullet that was dropped and went straight down.  In other words, its forward motion does not decrease the force that gravity exerts on it.

 

Of course this would not be true if I aimed the rifle straight up, straight down, or at a 45 degree angle from straight up.  But in each case the force of gravity (which varies with distance from the source of the gravity) would be the same.  The force of gravity, as such, wouldn't change, but the force provided by the explosion of the bullet shell would serve to partially and temporarily "overcome" the force.

 

If a ballistic missile were fired on a level line from a high enough altitude (say a mountain top) and with a high enough speed it might "never" hit the ground at all (due to the curvature of the earth). As it goes "forward" it is also "falling," just like the bullet. But with enough speed it will end up in orbit (perpetual free fall) around the earth. Again, that is because the earth is a curved sphere.  But it would still be held in orbit by the force of gravity.

Edited April 26, 2018 by Moronium

[Moronium]

Just to take it a step further, Hazel, I will add this.

 

1.  As you know, the "force" of gravity decreases with distance, so the higher you go up in space (away from the earth's center of gravity) the less force it will exert on you.

 

2.  If you fire a rocket at a high enough speed (higher than the escape velocity), it can escape the earth's gravity entirely and go on to the moon or just into outer space beyond the solar system.  That is because the force of gravity is steadily decreasing with each mile (or inch) further away from earth you go.

 

3.  But there is an in-between speed such that the rocket never returns to earth, but never entirely escapes the earth's gravitational "pull" either.  That's where satellites reside (in orbit).  Their "forward momentum" is still enough that (due to the earth's curvature) they never return to earth.   But it does not require more "energy" for them to remain in orbit.  They are, essentially, "just coasting" at that point.  They can remain in orbit in perpetuity without requiring "more energy" for them to keep going.  The earth is a satellite of the sun and has been orbiting it for eons, for example.  The earth has reached an equilibrium with the sun where it's (inertial) "forward motion" is sufficient to keep it from descending into the sun, but not enough for it to entirely escape the sun's gravity and leave the solar system.

 

4.  All that is kinda oversimplified, but I am trying to address the portion of your question where you asked about "expending some of its own energy in "free fall."  Both an orbiting satellite and an object which is falling but will strike the earth are in "free fall."  In gross terms, though, gravity is exerting a greater force upon the object which will "return" to earth, because it's closer and will just continue getting more close all the time (until it strikes the earth's surface).  But when in free fall, neither one is "expending its own energy" and both are just moving under the effects of gravity.

 

I may not have said all that in a way that makes much sense to you, I don't know.

Edited April 26, 2018 by Moronium

[Moronium]

As a side note that is not particularly relevant, we can, and have, put satellites in space which do not orbit the earth.  Instead they orbit the sun, just like earth does.  This comes in handy for making a number of scientific measurements, such as ones utilizing parallax. 

 

Those satellites are also in "free fall."  The difference is that the gravitational force which they are acting under is primarily that of the sun, not the earth.

[JMJones0424]

Wouldn't gravity exert less force on a falling ball than on an arced ball, the former expending some of its own energy in "free fall" and the later using only gravity's force?

This is a very good question.

 

It makes sense that if I propel an object out with some amount of force, let's say by shooting a bullet out of a rifle, that it contains more energy than an object that I drop at the same time.  The problem, I think, here is in definition of terms.  Neither the bullet I fired nor the bullet I dropped is compelled to fall towards the Earth due to any force I imparted to it.  In fact, If you could negate the effects of air, the bullet I fired from the rifle parallel to the ground would strike the ground at the same time as the bullet I dropped.  If you are familiar with how rifles are zeroed in for different ranges, then you should know that the path that a bullet follows is not a line, but rather an arc that continuously falls short of the point that the rifle was aimed at.  The rate that it falls short is the same as if it wasn't fired at all.  The forward momentum of the bullet does not in any way affect the rate at which it falls towards the Earth.  This is why you need to adjust for range when firing at a target, and why the further the range, the greater the upward angle required.

 

The very same thing can be experienced when shooting basketballs at a hoop, or when kicking soccer balls, or when driving golf balls.  As soon as you stop imparting force on an object, it begins to accelerate towards the Earth.  This rate of acceleration is not at all affected by the force you imparted on the object.

 

Objects don't orbit the Earth because we impart enough velocity in order to overcome gravity.  They orbit because they are moving forward faster than or equal to the rate that they are falling. If the Saturn V launched straight up, it would fall back to Earth.  The reason why it could orbit the Earth and continue on to the Moon is that it moved forward relative to the Earth faster than it fell towards the Earth.

 

Gravity imparts precisely the same force on an arced ball as it does on a dropped ball, as all objects that aren't being supported by some structure or force are in free fall.  This includes objects that are moving "up".  A thrown ball (unlike a rocket) no longer has anything imparting force on it other than gravity.  Even while it may be moving "up", it is in freefall and is accelerating towards the center of the Earth.  A better description is that it is on an orbit around the center of the Earth, and if the mass of the Earth was represented as a point mass, then the arc a ball follows is an arc of that orbit until it strikes the surface of the Earth.

 

I cannot more highly recommend ASU's hyperphysics site. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

It is an easily understandable overview of basic physics concepts and I find it useful for understanding concepts that don't immediately seem obvious.

 

Alternatively, try playing around with Kerbal Space Program.  It is a sandbox game that deals with orbital and aerodynamic physics and I have learned quite a bit just by playing around with it.

Edited April 27, 2018 by JMJones0424

[hazelm]

This is a very good question.

 

It makes sense that if I propel an object out with some amount of force, let's say by shooting a bullet out of a rifle, that it contains more energy than an object that I drop at the same time.  The problem, I think, here is in definition of terms.  Neither the bullet I fired nor the bullet I dropped is compelled to fall towards the Earth due to any force I imparted to it.  In fact, If you could negate the effects of air, the bullet I fired from the rifle parallel to the ground would strike the ground at the same time as the bullet I dropped.  If you are familiar with how rifles are zeroed in for different ranges, then you should know that the path that a bullet follows is not a line, but rather an arc that continuously falls short of the point that the rifle was aimed at.  The rate that it falls short is the same as if it wasn't fired at all.  The forward momentum of the bullet does not in any way affect the rate at which it falls towards the Earth.  This is why you need to adjust for range when firing at a target, and why the further the range, the greater the upward angle required.

 

The very same thing can be experienced when shooting basketballs at a hoop, or when kicking soccer balls, or when driving golf balls.  As soon as you stop imparting force on an object, it begins to accelerate towards the Earth.  This rate of acceleration is not at all affected by the force you imparted on the object.

 

Objects don't orbit the Earth because we impart enough velocity in order to overcome gravity.  They orbit because they are moving forward faster than or equal to the rate that they are falling. If the Saturn V launched straight up, it would fall back to Earth.  The reason why it could orbit the Earth and continue on to the Moon is that it moved forward relative to the Earth faster than it fell towards the Earth.

 

Gravity imparts precisely the same force on an arced ball as it does on a dropped ball, as all objects that aren't being supported by some structure or force are in free fall.  This includes objects that are moving "up".  A thrown ball (unlike a rocket) no longer has anything imparting force on it other than gravity.  Even while it may be moving "up", it is in freefall and is accelerating towards the center of the Earth.  A better description is that it is on an orbit around the center of the Earth, and if the mass of the Earth was represented as a point mass, then the arc a ball follows is an arc of that orbit until it strikes the surface of the Earth.

 

I cannot more highly recommend ASU's hyperphysics site. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

It is an easily understandable overview of basic physics concepts and I find it useful for understanding concepts that don't immediately seem obvious.

 

Alternatively, try playing around with Kerbal Space Program.  It is a sandbox game that deals with orbital and aerodynamic physics and I have learned quite a bit just by playing around with it.

I am smiling at those last two statements.  My reply would be  a long, meandering topic.   I'll skip it.   But this, which you said, is the key.  Before you can understand any topic, you need a good understanding of the terms and that isn't always easy in a subject like physics. 

 

Thank you for the post.  Good explanation.  As with Moronium's posts, I need to first get the effects of air on the balls before anything more.  The two are said to cancel each other out.  It is on this forum.  I just need time to go back to it.

[JMJones0424]

Have you heard the joke about the horse breeder that was trying to come up with a winning line.  His best friend was a world renowned theoretical physicist and the smartest person he knew.  He asked her how to use physics to come up with the best breeding and training program.  She gave it a lot of thought and finally responded, "First, assume the horse is a sphere on a frictionless plane".

 

The effects of air on the balls don't matter if you can avoid it, and that's the point.  Air doesn't matter in gravitational attraction, and the better you can eliminate air interactions, the better you can measure what you are after.  Don't think too hard about this, it's really quite simple.  Go out and drop a few things and observe how they fall.  I am willing to bet that your intuition of how things fall isn't as good as your intuition of how things move when pushed.

[Moronium]

 I need to first get the effects of air on the balls before anything more.  The two are said to cancel each other out.  It is on this forum.  I just need time to go back to it.

 

 

Most of the general statements made about gravity kinda tacitly presuppose a vacuum.  The atmosphere (air) can serve to slow a falling object's free fall, but that not because the force of gravity is any more or less--it's just the circumstances.

 

What you've "heard" about air "cancelling out" gravity probably relates to "terminal velocity":

 

In a vacuum an object in free fall will just continue accelerating (going faster all the time).  But when you're going through some kind of tangible medium, like air, the acceleration will cease at a certain point, due to the "air resistance."

 

As I recall, the "terminal velocity" for a skydiver is about 200 mph, for example, but that's ONLY IF he's laid out flat, with his stomach to the earth.  If he makes a pointed "dive," like he might off a diving board at the pool, he can go faster than that because that lessens the "drag" of the atmosphere.

 

But air resistance never "cancels out" the pull of gravity.  He's still going 200+ miles per hour toward the earth, due to the pull of gravity.  It is only the continued acceleration that stops.  Depending of the height he jumped from, his speed might otherwise have been, say, 500 mph by the time he hit the ground.  Either way, the poor chump is gunna die if his parachute doesn't open.  Thanks, gravity.

Edited April 27, 2018 by Moronium

[hazelm]

Most of the general statements made about gravity kinda tacitly presuppose a vacuum.  The atmosphere (air) can serve to slow a falling object's free fall, but that not because the force of gravity is any more or less--it's just the circumstances.

 

What you've "heard" about air "cancelling out" gravity probably relates to "terminal velocity":

 

In a vacuum an object in free fall will just continue accelerating (going faster all the time).  But when you're going through some kind of tangible medium, like air, the acceleration will cease at a certain point, due to the "air resistance."

 

As I recall, the "terminal velocity" for a skydiver is about 200 mph, for example, but that's ONLY IF he's laid out flat, with his stomach to the earth.  If he makes a pointed "dive," like he might off a diving board at the pool, he can go faster than that because that lessens the "drag" of the atmosphere.

 

But air resistance never "cancels out" the pull of gravity.  He's still going 200+ miles per hour toward the earth, due to the pull of gravity.  It is only the continued acceleration that stops.  Depending of the height he jumped from, his speed might otherwise have been, say, 500 mph by the time he hit the ground.  Either way, the poor chump is gunna die if his parachute doesn't open.  Thanks, gravity.

Thank you for the review.  I think your last paragraph relates to "cancels" each other out.  Gravity pulls down and speeds the falling body down.  Air holds it up.  I am not sure that's right but .

 

I had thought the description of two bodies falling at the same speed was in a vacuum.  But someone somewhere along the line corrected that.

Edited April 27, 2018 by hazelm

[Moronium]

 

I had thought the description of two bodies falling at the same speed was in a vacuum.  But someone somewhere along the line corrected that.

 

 

I didn't see anyone "correct" you about that, but in any case no "correction" is needed.

 

I think someone, maybe Jim, posted a link to video involving a feather (which I didn't look at, so I'm not sure what's in it).

 

In a vacuum, both a feather and a 50 pound lead ball WILL fall at the same rate.

 

It is the "air resistance" (taken together with its disproportionate surface area) that causes a feather to fall slower in the atmosphere.  It is not because it is of slight weight.

Edited April 27, 2018 by Moronium