physics concept quesiton

[Titan]

I understand the math. I just dispute the present definition of acceleration. The universe is not a place governed by math. Our math is a result of understanding the universe. Forces are a more fundamental idea in Physics than acceleration. So I say, knowing how forces work, "acceleration" implies and means the resultant motion of an object due to a force. And "Force" describes one of our known forces, in this case gravity.

Clear?

 

[Mo0o]

In the end the math doesn't lie:

X=VoT + .5 AT^2
dX/dT = V = Vo + AT
dV/dT = A

 

[dighn]

Originally posted by: Titan
I understand the math. I just dispute the present definition of acceleration. The universe is not a place governed by math. Our math is a result of understanding the universe. Forces are a more fundamental idea in Physics than acceleration. So I say, knowing how forces work, "acceleration" implies and means the resultant motion of an object due to a force. And "Force" describes one of our known forces, in this case gravity.

Clear?

no, not at all. but whatever.

 

[Mo0o]

Originally posted by: Titan
I understand the math. I just dispute the present definition of acceleration. The universe is not a place governed by math. Our math is a result of understanding the universe. Forces are a more fundamental idea in Physics than acceleration. So I say, knowing how forces work, "acceleration" implies and means the resultant motion of an object due to a force. And "Force" describes one of our known forces, in this case gravity.

Clear?

no not really. according to one of the most fundamental laws of newtonian physics, F=MA. In the presence of a net force there WILL be an non zero acceleration. And my definition of acceleration is the change in mometum.

 

[Titan]

Originally posted by: Mo0o
In the end the math doesn't lie:

X=VoT + .5 AT^2
dX/dT = V = Vo + AT
dV/dT = A

No, the language lies. Acceleration, to me, is a measurement of phenomena, motion. I don't care if you think i'm right or wrong. The point out of all this is that our language is so inadequate that we need more insight from the asker of the question. If they threw the word "resulting" acceleration in there, it would change things, right? I see that word as implied.

If you were an engineer and asked this question, you would make sure and ask for clarification. Otherwise people may die.

I'm looking at it from the practical slant. At rest, what does an accelerometer measure?

 

[Mo0o]

Originally posted by: Titan

Originally posted by: Mo0o
In the end the math doesn't lie:

X=VoT + .5 AT^2
dX/dT = V = Vo + AT
dV/dT = A

No, the language lies. Acceleration, to me, is a measurement of phenomena, motion. I don't care if you think i'm right or wrong. The point out of all this is that our language is so inadequate that we need more insight from the asker of the question. If they threw the word "resulting" acceleration in there, it would change things, right? I see that word as implied.

What the hell are you talking about. Even if you define acceleration as a measurement of motion, FINE. By acceleration is the CHANGE in the rate of motion over time. So if the bullet is at zero velocity at its apex, then 1 second later it's moving 9.81m/s , its during that entire time is 9.81m/s^2. The language lies? That's not even a valid argument, how can the language lie? It's mathematics derived from one of the fundamental laws of newtonian physics, that's what we're arguinig here by the way, so I'm not sure how you can say it lies

 

[silverpig]

With no additional information all answers are both correct and incorrect

Assuming the particle is near the earth's surface, the answer is b.

 

[Titan]

Mo0o, If the language wasn't stark black and white truth, you and I would not be arguing at this time. The question is also flawed because we have no scientific definition of an instant. Which could be a reason to support your claim cceleration is constant. I hope I have demonstrated I know something about what i'm talking about.

One other point. Time is not discreet. It is continuous. That is why we use calculus to determine and predict motion.

I look at it from the other way. The practical way, not what the formula says, but what answer does the asker need? How did the object travel upward? What caused its velocity to reach zero? The answer is forces. In any useful term, what is its resultant acceleration?

When mass remains constant, F = ma. The force of gravity at the surface of the earth is approximately 9.8m/s^2.

Let's try a more interesting hypothetical question. Assume by magical means, at it's apex, the object loses all mass. What will it's acceleration be? The force of gravity is still acting upon it.

I just look at everything as forces. In this case, the forces are constant, and the motion changes.

 

[Mo0o]

Originally posted by: Titan
Mo0o, If the language wasn't stark black and white truth, you and I would not be arguing at this time. The question is also flawed because we have no scientific definition of an instant. Which could be a reason to support your claim cceleration is constant. I hope I have demonstrated I know something about what i'm talking about.

One other point. Time is not discreet. It is continuous. That is why we use calculus to determine and predict motion.

I look at it from the other way. The practical way, not what the formula says, but what answer does the asker need? How did the object travel upward? What caused its velocity to reach zero? The answer is forces. In any useful term, what is its resultant acceleration?

When mass remains constant, F = ma. The force of gravity at the surface of the earth is approximately 9.8m/s^2.

Let's try a more interesting hypothetical question. Assume by magical means, at it's apex, the object loses all mass. What will it's acceleration be? The force of gravity is still acting upon it.

I just look at everything as forces. In this case, the forces are constant, and the motion changes.

Well the object didn't lose its mass. And if for some magical reason the object managed to exist in absence of mass, it would not accelerate. It would simply sit there or continue on its x coordinate velocity.

 

[Eeezee]

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

Wrong wrong wrong! Acceleration LEADS TO movement. You're confusing acceleration with velocity. Momentum is NOT a force. I sincerely hope that you aren't in a field that requires knowledge of these things.

F = ma = mg (in the case of gravity)
Therefore a = g

 

[Eeezee]

Originally posted by: Titan
I understand the math. I just dispute the present definition of acceleration. The universe is not a place governed by math. Our math is a result of understanding the universe. Forces are a more fundamental idea in Physics than acceleration. So I say, knowing how forces work, "acceleration" implies and means the resultant motion of an object due to a force. And "Force" describes one of our known forces, in this case gravity.

Clear?

The particle takes 2 seconds to reach its highest point. This implies that there is an acceleration downward, otherwise it would never reach its highest point (it would always go up at constant velocity).

If a = 0, then dv/dt = 0, which means that your change in velocity is zero. If you experience no change in velocity, then you will continue moving in the same direction at the same speed forever. Objects in motion stay in motion. You may want to review your kinematic equations if this is at all confusing.

This is actually a trick question, you can not know the particle's acceleration because you don't know what planet you're on or if the particle is massive enough to significantly feel the effects of gravity (for example, if it's in a strong electric field and has a charge then gravity is negligible).

Let's say we're talking about a soccer ball on Earth. The scenario is a child throwing the ball straight up in the air. The acceleration throughout its entire motion after its release from the kid's hands is 9.8 m/s^2 pointing towards the Earth's center of mass (straight down).

You keep talking about Newton and how he's so great, but then you say that his math is wrong and that a change in velocity must imply 0 acceleration? That goes against Newton's fundamental equation, that a = dv/dt! Not only that, but he also came up with the law of gravity.

F = -G*m*M/r^2 rhat = ma
a = -G*M/r^2 = g = -9.8 m/s^2 rhat

 

[Eeezee]

Originally posted by: Titan

Originally posted by: Mo0o
In the end the math doesn't lie:

X=VoT + .5 AT^2
dX/dT = V = Vo + AT
dV/dT = A

No, the language lies. Acceleration, to me, is a measurement of phenomena, motion. I don't care if you think i'm right or wrong. The point out of all this is that our language is so inadequate that we need more insight from the asker of the question. If they threw the word "resulting" acceleration in there, it would change things, right? I see that word as implied.

If you were an engineer and asked this question, you would make sure and ask for clarification. Otherwise people may die.

I'm looking at it from the practical slant. At rest, what does an accelerometer measure?

Velocity is a measurement of motion. Acceleration is a measurement of a change in motion.

 

[Eeezee]

Originally posted by: Titan
Mo0o, If the language wasn't stark black and white truth, you and I would not be arguing at this time. The question is also flawed because we have no scientific definition of an instant. Which could be a reason to support your claim cceleration is constant. I hope I have demonstrated I know something about what i'm talking about.

One other point. Time is not discreet. It is continuous. That is why we use calculus to determine and predict motion.

I look at it from the other way. The practical way, not what the formula says, but what answer does the asker need? How did the object travel upward? What caused its velocity to reach zero? The answer is forces. In any useful term, what is its resultant acceleration?

When mass remains constant, F = ma. The force of gravity at the surface of the earth is approximately 9.8m/s^2.

Let's try a more interesting hypothetical question. Assume by magical means, at it's apex, the object loses all mass. What will it's acceleration be? The force of gravity is still acting upon it.

I just look at everything as forces. In this case, the forces are constant, and the motion changes.

Okay, so the object now has no mass. In this case, there would be no acceleration. The original problem, however, is obviously geared toward an intro physics course involving the Earth's gravitational field. The language is not meant to be read into any more than necessary. You can assume that there's a damped harmonic oscillator or a means of removing almost all mass from the particle or some extran force field that kicks in suddenly at t=2, but that's drastically overcomplicating things.

Your "practical" explanation for acceleration is nothing more than dancing around the bush. You forgot how to solve an intro physics problem, and that's okay (assuming you're in a field that does not require you to know this). The best way to solv ean intro physics problem is to make some assumptions that would result in the problem becoming incredibly easy.

Assume that there is only 1 force (gravity). Assume the particle does not lose or gain mass. Assume that the particle had some initial upward velocity and that the acceleration was constant at all times in its travel. After that, the problem is trivial. Those of us who solved the problem correctly all followed these steps, and these are the correct steps.

 

[Titan]

Originally posted by: Mo0o

Originally posted by: Titan
Mo0o, If the language wasn't stark black and white truth, you and I would not be arguing at this time. The question is also flawed because we have no scientific definition of an instant. Which could be a reason to support your claim cceleration is constant. I hope I have demonstrated I know something about what i'm talking about.

One other point. Time is not discreet. It is continuous. That is why we use calculus to determine and predict motion.

I look at it from the other way. The practical way, not what the formula says, but what answer does the asker need? How did the object travel upward? What caused its velocity to reach zero? The answer is forces. In any useful term, what is its resultant acceleration?

When mass remains constant, F = ma. The force of gravity at the surface of the earth is approximately 9.8m/s^2.

Let's try a more interesting hypothetical question. Assume by magical means, at it's apex, the object loses all mass. What will it's acceleration be? The force of gravity is still acting upon it.

I just look at everything as forces. In this case, the forces are constant, and the motion changes.

Well the object didn't lose its mass. And if for some magical reason the object managed to exist in absence of mass, it would not accelerate. It would simply sit there or continue on its x coordinate velocity.

Exactly. I'll condede the math is on your side for an answer. But what does it mean? I would say your answer means there is an outside force contunuously acting on an object of mass. But I question what kind of answer the asker wanted. That is how I knew what to answer and got 100s on my physics tests.

I only persist because I am not one of those people who believes math has all the answers. If you look at history, math did not create science, it is the other way around. Newton had an ah-ha moment about the nature of forces in our universe then used math and language to describe it. They can both be limiting and confusing in the practical world. And history has also shown that these forumlas need revision to put them into context. We could try to discuss what things would be like without history, but that would be downright absurd.

No real scienctist should believe all answers lie on the multiple choice list. Tests at school are more or less a game within a game played by us, humans. The real world is out there. Not on paper in a math or physics book.

Other answers that I would consider true is

E) Undefined. Due to quantum uncertainty, the object could simultaneously exist in another space affected by different forces at any given instant.
F) Relative to itself, the object is not accelerating anywhere.
G)Unknown, question does not specify a reference frame.
H) Unknown, exact elevation above the earth's surface is not specified.
I) The curvature of space-time requires more information.
J) The question does not specify the reference frame and could be asking the acceleration of orbiting electrons, determined by charge and the weak force.

You point to the box. I acknowledge it's there and it seems to suit you. But I am not getting in it. I enjoy the color out here.

 

[Mo0o]

Originally posted by: Titan

Originally posted by: Mo0o

Originally posted by: Titan
Mo0o, If the language wasn't stark black and white truth, you and I would not be arguing at this time. The question is also flawed because we have no scientific definition of an instant. Which could be a reason to support your claim cceleration is constant. I hope I have demonstrated I know something about what i'm talking about.

One other point. Time is not discreet. It is continuous. That is why we use calculus to determine and predict motion.

I look at it from the other way. The practical way, not what the formula says, but what answer does the asker need? How did the object travel upward? What caused its velocity to reach zero? The answer is forces. In any useful term, what is its resultant acceleration?

When mass remains constant, F = ma. The force of gravity at the surface of the earth is approximately 9.8m/s^2.

Let's try a more interesting hypothetical question. Assume by magical means, at it's apex, the object loses all mass. What will it's acceleration be? The force of gravity is still acting upon it.

I just look at everything as forces. In this case, the forces are constant, and the motion changes.

Well the object didn't lose its mass. And if for some magical reason the object managed to exist in absence of mass, it would not accelerate. It would simply sit there or continue on its x coordinate velocity.

Exactly. I'll condede the math is on your side for an answer. But what does it mean? I would say your answer means there is an outside force contunuously acting on an object of mass. But I question what kind of answer the asker wanted. That is how I knew what to answer and got 100s on my physics tests.

I only persist because I am not one of those people who believes math has all the answers. If you look at history, math did not create science, it is the other way around. Newton had an ah-ha moment about the nature of forces in our universe then used math and language to describe it. They can both be limiting and confusing in the practical world. And history has also shown that these forumlas need revision to put them into context. We could try to discuss what things would be like without history, but that would be downright absurd.

No real scienctist should believe all answers lie on the multiple choice list. Tests at school are more or less a game within a game played by us, humans. The real world is out there. Not on paper in a math or physics book.

Other answers that I would consider true is

E) Undefined. Due to quantum uncertainty, the object could simultaneously exist in another space affected by different forces at any given instant.
F) Relative to itself, the object is not accelerating anywhere.
G)Unknown, question does not specify a reference frame.
H) Unknown, exact elevation above the earth's surface is not specified.
I) The curvature of space-time requires more information.
J) The question does not specify the reference frame and could be asking the acceleration of orbiting electrons, determined by charge and the weak force.

You point to the box. I acknowledge it's there and it seems to suit you. But I am not getting in it. I enjoy the color out here.

So on a standardized test you would just leave the answer blank? Create your own bubbles?

 

[Titan]

Eeezee, I know all this. You don't have to give me remedial physics. I have condeded that 9.8 looks ok on paper. But I honestly ask you what use is that information to an engineer, or anybody for that matter? I look for the deeper meaning, which has to do with forces. It tells us there is a force we need to know about.

Or to answer your other statement, how do you measure acceleration? Predict it with a formula, or use an instrument?

I'm looking at the big picture, and remembering the fundamentals of how science works.

I say the question is ambiguous. But people are, so you need to know them.

 

[Titan]

Originally posted by: Mo0o
[So on a standardized test you would just leave the answer blank? Create your own bubbles?

Pretty much. I hate standardized tests because I am not acquainted with the asker of the question. I am a much more personable engineer than most. I always did great in school because I got to know the teacher. On standardized tests I was often confronted with my own creativity and didn't know which direction to go. being an engineer, I am practical, and want to know what use something has to me, otherwise, I don't care what you write on paper. I really enjoy physics because I relate to it on a personal level. I understand angular momentum and rotational inertia better than most. I am cpable of focusing to a point, or panning out to view the big picture. I like the big picture, it's more wondrous and fun.

 

[Mo0o]

Originally posted by: Titan
Eeezee, I know all this. You don't have to give me remedial physics. I have condeded that 9.8 looks ok on paper. But I honestly ask you what use is that information to an engineer, or anybody for that matter? I look for the deeper meaning, which has to do with forces. It tells us there is a force we need to know about.

Or to answer your other statement, how do you measure acceleration? Predict it with a formula, or use an instrument?

I'm looking at the big picture, and remembering the fundamentals of how science works.

I say the question is ambiguous. But people are, so you need to know them.

Given all this "deep" physics talk, it's surprising you gave such a terrible initial answer of the acceleration somehow being zero because velocity is zero

 

[eits]

c, duh.

the particle is stationary in mid-air at it's highest point (with respect to the y-axis)...

 

[Titan]

Originally posted by: Mo0o

Originally posted by: Titan
Eeezee, I know all this. You don't have to give me remedial physics. I have condeded that 9.8 looks ok on paper. But I honestly ask you what use is that information to an engineer, or anybody for that matter? I look for the deeper meaning, which has to do with forces. It tells us there is a force we need to know about.

Or to answer your other statement, how do you measure acceleration? Predict it with a formula, or use an instrument?

I'm looking at the big picture, and remembering the fundamentals of how science works.

I say the question is ambiguous. But people are, so you need to know them.

Given all this "deep" physics talk, it's surprising you gave such a terrible initial answer of the acceleration somehow being zero because velocity is zero

In your judgment it's "terrible." In mine it's practical. I'm not judging your answer. We looked at it from very different contexts. I picture someone with high-speed camera measuring an object determining its acceleration. You picture the equation. We disagree on what the question as really asking. For a physics class where it usually boils down to numbers, i'll admidt you probably got the answer "right." Note the original post, which is what I read, did not specify this was for a class. It could have been Mythbusters. But out in the "real" world where science is determined by measurements, I am thinking of people measuring n object, and that could be what the word acceleration describes.

 

[Mo0o]

Originally posted by: Titan

Originally posted by: Mo0o

Originally posted by: Titan
Eeezee, I know all this. You don't have to give me remedial physics. I have condeded that 9.8 looks ok on paper. But I honestly ask you what use is that information to an engineer, or anybody for that matter? I look for the deeper meaning, which has to do with forces. It tells us there is a force we need to know about.

Or to answer your other statement, how do you measure acceleration? Predict it with a formula, or use an instrument?

I'm looking at the big picture, and remembering the fundamentals of how science works.

I say the question is ambiguous. But people are, so you need to know them.

Given all this "deep" physics talk, it's surprising you gave such a terrible initial answer of the acceleration somehow being zero because velocity is zero

In your judgment it's "terrible." In mine it's practical. I'm not judging your answer. We looked at it from very different contexts. I picture someone with high-speed camera measuring an object determining its acceleration. You picture the equation. We disagree on what the question as really asking. For a physics class where it usually boils down to numbers, i'll admidt you probably got the answer "right." But out in the "real" world where science is determined by measurements, I am thinking of people measuring n object, and that could be what the word acceleration describes.

But if you shot pictures of the bullet as it went to the apex then back down and had the height/time data, you should be abel to derive an acceleration can't you? Pulling out hte pictures of the bullet at its apex isn't enough evidence to say whetheri ts accelerating or not.

Ive done this in physics lab where we toss a ball in the air and had a video camera. You can derive the time and height of the ball and calculate a trajectory which lets you find acceleration

 

[Titan]

Originally posted by: Mo0o

But if you shot pictures of the bullet as it went to the apex then back down and had the height/time data, you should be abel to derive an acceleration can't you? Pulling out hte pictures of the bullet at its apex isn't enough evidence to say whetheri ts accelerating or not.

Ive done this in physics lab where we toss a ball in the air and had a video camera. You can derive the time and height of the ball and calculate a trajectory which lets you find acceleration

You and I are literally down to what we each think the word "acceleration" means. According to the mathematic definition you seem to be correct. This could go on forever. You think it is a cause, and I think it is an effect, caused by forces. I think I've been over this before. To me, forces cause acceleration. And there are questions about reference framse. Right now my butt is not accelerating though my chair despite the force of gravity, due to counteracting forces. But that will soon change because I am tired of discussing this and have made it very clear that I interpreted the language differently. And at the end of the day, we all have to intrepret what Cheny meant when he said he shot that guy in the face.

 

[Eeezee]

Originally posted by: Titan

Originally posted by: Mo0o

But if you shot pictures of the bullet as it went to the apex then back down and had the height/time data, you should be abel to derive an acceleration can't you? Pulling out hte pictures of the bullet at its apex isn't enough evidence to say whetheri ts accelerating or not.

Ive done this in physics lab where we toss a ball in the air and had a video camera. You can derive the time and height of the ball and calculate a trajectory which lets you find acceleration

You and I are literally down to what we each think the word "acceleration" means. According to the mathematic definition you seem to be correct. This could go on forever. You think it is a cause, and I think it is an effect, caused by forces. I think I've been over this before. To me, forces cause acceleration. And there are questions about reference framse. Right now my butt is not accelerating though my chair despite the force of gravity, due to counteracting forces. But that will soon change because I am tired of discussing this and have made it very clear that I interpreted the language differently. And at the end of the day, we all have to intrepret what Cheny meant when he said he shot that guy in the face.

In other words, you fvcked up your first answer and need to endlessly backpedal on semantics in order to make yourself feel better. Hell, a bunch of your other "possible" answers were wrong too. For example

F) Relative to itself, the object is not accelerating anywhere.
That's not what the problem asked for. If we were considering a reference frame relative to the object, then the problem would not have stated that the object reaches a maximum height. The object is moving relative to the observer, therefore we are not considering its reference frame.

I) The curvature of space-time requires more information.
Zoom in on any curve enough and it becomes a straight line. You do not require any more information than is provided.

What, do you want to suppose that the particle is moving at near relativistic speeds? How about if there are external fields of force? What if the particle is in a crystal lattice and is at the edge of the Brillouin zone?

No, you're using useless speculation to cover up your mistake. There are about a dozen comments of yours in this thread that are erroneous in one way or another. For example, you said that acceleration must be zero if velocity is zero, I'm sorry but you're wrong. It's okay, we forgive you.

 

[eits]

how the hell is this a 5-paged thread? the answer is c. it's over. done. no debate. let it die.

answer = c.... 0.

the end.

 

[Brainonska511]

Originally posted by: eits
how the hell is this a 5-paged thread? the answer is c. it's over. done. no debate. let it die.

answer = c.... 0.

the end.

No, you're wrong. The answer is B. Gravity is always a constant in these simple physics problems (and F = ma=mg). And just because velocity is 0, doesn't mean that accelation is 0. The magnitude of the acceleration is 9.8m/s^2. I don't know why there is so much arguement about this simple little physics question.