Science questions

[DrPizza]

Originally posted by: Astaroth33
The correct answer is that the only force that's really exerted here is God's Will. The pen falls because the Intelligent Designer wills it. The Volkswagon isn't exerting any force, but rather, the it is God's Will that the SUV move slowly.

All science is an illusion, a mode of thinking specifically designed to seperate people from their faith in God.

:laugh:

 

[RaynorWolfcastle]

<devil's advocate>
I don't really understand why you say the forces are equal: F = ma. Let's say the 250 lb lineman exerts force F1 (of mass m1) on the lighter lineman (of mass m2) that exerts F2 back where F1 > F2. This means that both linemen will begin to accelerate such that F1-F2 = (m1+m2)*a is satisfied not that F1 = F2. Either way, I understand what you meant by your question but it IS poorly worded as others have stated.

That being said, the weight of the linesmen has strictly nothing to do with the forces they exert on each other. Weight defined as "the vertical force exerted by a mass as a result of gravity" and has absolutely nothing to do with the horizontal forces being exerted unless you start considering friction and use a more complex model for where and how the forces get exerted. In the case of car and the SUV, the weight car has even less to do with anything as rolling motion is assumed and we are not concerned with the acceleration.
</devil's advocate>

 

[DrPizza]

Originally posted by: RaynorWolfcastle
<devil's advocate>
I don't really understand why you say the forces are equal: F = ma. Let's say the 250 lb lineman exerts force F1 (of mass m1) on the lighter lineman (of mass m2) that exerts F2 back where F1 > F2. This means that both linemen will begin to accelerate such that F1-F2 = (m1+m2)*a is satisfied not that F1 = F2. Either way, I understand what you meant by your question but it IS poorly worded as others have stated.

That being said, the weight of the linesmen has strictly nothing to do with the forces they exert on each other. Weight defined as "the vertical force exerted by a mass as a result of gravity" and has absolutely nothing to do with the horizontal forces being exerted unless you start considering friction and use a more complex model for where and how the forces get exerted. In the case of car and the SUV, the weight car has even less to do with anything as rolling motion is assumed and we are not concerned with the acceleration.
</devil's advocate>

Huh?? What do you mean "devil's advocate"?
If you mean you're providing an incorrect explanation for the sake of eliciting a discussion, your argument has already been discussed.
Your equation F1-F2 = (m1+m2)*a is incorrect with the forces F1 and F2 being as I described and as you described. Furthermore, F1 must equal F2.

Now, if there was a big block sitting in the middle of the field, and F1 and F2 were the forces being applied to the block (in opposite directions) by the two players, then, yes, the block would accelerate according to your equation (if there's no friction acting on the block)

However, (I'm starting to feel like a broken record) The force that player one exerts on the box = F1. The magnitude of the force the box exerts on player one is ALSO = F1. These are the equal and opposite forces that Newton was talking about. Ditto for player 2.

Equal and opposite forces have nothing to do with the net forces acting on an object. Like a lot of other people, you're probably thinking of statics.

Look at it this way. I'll strap on a pair of rollerskates. I'll go up to the wall, and while facing the wall, I'm going to push against it with a 50 Newton force.
Explain why I move backwards. You can't, unless you consider that if I push against the wall, the wall is pushing against me. And, just how hard is it pushing against me... search for the number.... 50 Newtons? Yes.

What's the force that I exert on the surface of the earth? Grab a bathroom scale, stick it under me, and it'll say somewhere around 900 Newtons. (actually, it'll give my mass in kilograms... but it's really measuring force, not mass. The manufacturer just divided by 9.8 m/s^2 so that a person could know their mass) What is the force that the earth is exerting against my feet? That's a tough one. Turn the bathroom scale upside down and measure 🙂 Ohhh, it reads the same amount?

 

[l Xes l]

rofl.. we never went to the moon..

 

[DrPizza]

Originally posted by: krnxpride83
rofl.. we never went to the moon..

Yeah, I know. They just used a really really heavy feather, made out of lead for that video. And, they recorded it really fast, then play it back slow to make it appear that it was only accelerating at a rate of about 1/6th that on earth.



Besides, you can't beat this logic:

"the feather would float away"
"well, then, what kept the astronauts on the moon?"
"Heavy boots."
"AAhhh ha! Well, then, why didn't the heavy boots float away?!"
"Hey, that makes sense. They would have floated away. I guess we never went to the moon. That's the only logical explanation"

 

[Mik3y]

Originally posted by: Ronstang

Originally posted by: Dgital

Originally posted by: DingDingDao
3rd choice
3rd choice
3rd choice

And this is such basic physics that if teachers cannot get the right answer then they should not be teachers. No wonder our educational system sucks.

Oh and BTW....I have not been in the educational system where science was involved for over 15 years so I am not exposed to this kind of critical science related thought on a daily basis.

most teachers are generally not or nowhere near top of the class when graduating high school or college. the ones who are top of the class end up doing more sophisticated work. getting a teaching credential is easy as hell. all you teach are basics really or what the department tells you to, and everything you need to teach is right in the book that tells how how to teach.

 

[Cattlegod]

Your second question answers are terribly worded. You make it assume total power output, and not one vs. the other (even though it is asked in the question) it is misleading.

Next time review your science questions with the english teacher 🙂

edit: In the question you are looking for answer 3, however, there is nothing incorrect about the answer 2.

 

[RaynorWolfcastle]

All of what you said is absolutely correct (and I never said otherwise) but that still doesn't change the fact that the weight of either the players or the cars has absolutely 0 bearing on the questions (red herring, perhaps?) or on the forces being applied onto each other.

Secondly, I very clearly explained in my response why I think your question is poorly worded. In the case of the rollerblades, you exert a force on a wall, the wall exerts a force back on you of equal and oposite direction which is caused by the static friction between the wall and the ground meanwhile you're on wheels so there is rolling motion and you roll back. Obviously it all works out, when you take a wider view of the system.

In the end, my point (that you ignored) was that these questions are extremely pedantic and serve only to try to tell someone "AHA! You're wrong!". Let me put it this way, if you put numbers to these questions and asked these same people to describe what would happen, how many do you think would get it wrong? None, right? So what's the point of asking these questions if everyone understands basic Newtonian mechanics?

 

[DrPizza]

Originally posted by: Cattlegod
Your second question answers are terribly worded. You make it assume total power output, and not one vs. the other (even though it is asked in the question) it is misleading.

Next time review your science questions with the english teacher 🙂

edit: In the question you are looking for answer 3, however, there is nothing incorrect about the answer 2.

Yes, there is something incorrect with answer 2. It is IMPOSSIBLE for one to push on the other harder. The forces MUST be equal.

 

[DrPizza]

Originally posted by: RaynorWolfcastle
All of what you said is absolutely correct (and I never said otherwise) but that still doesn't change the fact that the weight of either the players or the cars has absolutely 0 bearing on the questions (red herring, perhaps?) or on the forces being applied onto each other.

Secondly, I very clearly explained in my response why I think your question is poorly worded. In the case of the rollerblades, you exert a force on a wall, the wall exerts a force back on you of equal and oposite direction which is caused by the static friction between the wall and the ground meanwhile you're on wheels so there is rolling motion and you roll back. Obviously it all works out, when you take a wider view of the system.

In the end, my point (that you ignored) was that these questions are extremely pedantic and serve only to try to tell someone "AHA! You're wrong!". Let me put it this way, if you put numbers to these questions and asked these same people to describe what would happen, how many do you think would get it wrong? None, right? So what's the point of asking these questions if everyone understands basic Newtonian mechanics?

The point of these questions is to point out that everyone DOESN'T understand basic Newtonian mechanics. If people understood "equal and opposite" then none of them would have gotten the 2nd or 3rd questions wrong. Their ability to parrot back to some high school or college teacher word for word Newton's 3rd law does not mean they understand the 3rd law. You are right that the weights of the players doesn't matter. If they believe that it does matter, then they don't understand Newton's 3rd law.


Also, allow me to point out that the following question is not a physics question, it's a mathematics question. "A unbalanced force of 10 Newtons pushes against a 5 kilogram mass. What is the resulting acceleration of the mass? Fnet = ma" If that's a physics question, then "If I have 3 quarks and I take one away, how many quarks do I have left?" isn't a 1st grade arithmetic problem, it's a quantum mechanics problem!

 

[RaynorWolfcastle]

Originally posted by: DrPizza

The point of these questions is to point out that everyone DOESN'T understand basic Newtonian mechanics. If people understood "equal and opposite" then none of them would have gotten the 2nd or 3rd questions wrong. Their ability to parrot back to some high school or college teacher word for word Newton's 3rd law does not mean they understand the 3rd law. You are right that the weights of the players doesn't matter. If they believe that it does matter, then they don't understand Newton's 3rd law.


Also, allow me to point out that the following question is not a physics question, it's a mathematics question. "A unbalanced force of 10 Newtons pushes against a 5 kilogram mass. What is the resulting acceleration of the mass? Fnet = ma" If that's a physics question, then "If I have 3 quarks and I take one away, how many quarks do I have left?" isn't a 1st grade arithmetic problem, it's a quantum mechanics problem!

"A 100 pound freshman lineman goes up against a 250 pound muscular lineman. The 250 pound lineman pushes with x Newtons while the 100 pound lineman pushes back with y newtons, where x > y > 0. Describe using Newtonian mechanics the resulting action of both linemen, you may assume that all forces are applied to the linesmens' centre of mass."

Would you consider this a valid physics question? I would, I and I bet most everyone you asked your question to would find the correct answer.

 

[DrPizza]

I find that to be a poorly written physics question, one that leads to the misconceptions I've noted. It's not worth arguing about though.

 

[Howard]

While accelerating, the net force is not 0, or so it seems. The normal force and force of gravity balance, but [taking "forward" as the positive direction] Fvolks - Fsuv (friction) > 0

Therefore Fvolks > Fsuv?

 

[DaShen]

333

 

[SMOGZINN]

Originally posted by: RaynorWolfcastle

Originally posted by: DrPizza

The point of these questions is to point out that everyone DOESN'T understand basic Newtonian mechanics. If people understood "equal and opposite" then none of them would have gotten the 2nd or 3rd questions wrong. Their ability to parrot back to some high school or college teacher word for word Newton's 3rd law does not mean they understand the 3rd law. You are right that the weights of the players doesn't matter. If they believe that it does matter, then they don't understand Newton's 3rd law.


Also, allow me to point out that the following question is not a physics question, it's a mathematics question. "A unbalanced force of 10 Newtons pushes against a 5 kilogram mass. What is the resulting acceleration of the mass? Fnet = ma" If that's a physics question, then "If I have 3 quarks and I take one away, how many quarks do I have left?" isn't a 1st grade arithmetic problem, it's a quantum mechanics problem!

"A 100 pound freshman lineman goes up against a 250 pound muscular lineman. The 250 pound lineman pushes with x Newtons while the 100 pound lineman pushes back with y newtons, where x > y > 0. Describe using Newtonian mechanics the resulting action of both linemen, you may assume that all forces are applied to the linesmens' centre of mass."

Would you consider this a valid physics question? I would, I and I bet most everyone you asked your question to would find the correct answer.

No, most people would get the answer half wrong. Most people would know that the 100lb lineman moves backwards, but few would tell you that the 250lb lineman has equal force exerted against him, and that is as important a part of the question as the movement of the 100lb lineman. I would bet that most people would tell you that the 100lb lineman has 250lb of force against him while the 250lb lineman has to only resist 100lb of force. In other words, they would tell you that it was a 1 to 2.5 ratio of force. This is clearly wrong.

 

[RaynorWolfcastle]

Originally posted by: SMOGZINN
No, most people would get the answer half wrong. Most people would know that the 100lb lineman moves backwards, but few would tell you that the 250lb lineman has equal force exerted against him, and that is as important a part of the question as the movement of the 100lb lineman. I would bet that most people would tell you that the 100lb lineman has 250lb of force against him while the 250lb lineman has to only resist 100lb of force. In other words, they would tell you that it was a 1 to 2.5 ratio of force. This is clearly wrong.

The point is that it really doesn't matter how you describe what happens in words as long as you understand what happens mathematically and can express the result as the players accelerating with a = (x - y)/(m1+m2). As I said in my other post, everything else is very pedantic as long as you can explain what happens and why.