Physics Question

PostmodernProphet said:
illogical......in a vertical situation there is only a force in one direction....the top is stationary...when it is horizontal there are two forces......
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You’re not viewing it correctly. There may be two forces acting on the scale but only one is acting on the scale spring. The other is acting to hold the scale stationary. If, for example, you suddenly removed the 100 N force from the spring the other 100 N force would pull the scale across the table and to the floor. However since there would be no force acting on the spring as it would fly across the table the scale would measure 0 N force. Does that explain why the scale would read 100N in this experiment?

The same applies if your holding the scale vertically. One force, your arm, holds the scale stationary and the other force acts upon the spring. If you removed the force from the spring the scale would move in the direction of the other force, your arm, but since no force is acting on the spring the scale would record 0 N force.
 
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Mott the Hoople said:
You’re not viewing it correctly. There may be two forces acting on the scale but only one is acting on the scale spring. The other is acting to hold the scale stationary. If, for example, you suddenly removed the 100 N force from the spring the other 100 N force would pull the scale across the table and to the floor. However since there would be force acting on the spring as it would fly across the table the scale would measure 0 N force. Does that explain why the scale would read 100N in this experiment?
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That doesn't mean anything to me Mott.

However the sum of the forces = 0. The same as if the scale were attached to the table.
 
Mott the Hoople said:
You’re not viewing it correctly. There may be two forces acting on the scale but only one is acting on the scale spring. The other is acting to hold the scale stationary. If, for example, you suddenly removed the 100 N force from the spring the other 100 N force would pull the scale across the table and to the floor. However since there would be no force acting on the spring as it would fly across the table the scale would measure 0 N force. Does that explain why the scale would read 100N in this experiment?

The same applies if your holding the scale vertically. One force, your arm, holds the scale stationary and the other force acts upon the spring. If you removed the force from the spring the scale would move in the direction of the other force, your arm, but since no force is acting on the spring the scale would record 0 N force.
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the only scale I am familiar with is my fishing scale.......no part is stationary......
 
Mott the Hoople said:
No, because then you have 100 N force applied to the spring. The scale would read 100 N force.
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No. The sum of the forces would = zero. The scale only measures force in one direction which of course = 100N. Whatever secures the spring scale applies an equal force in the opposite direction of 100N which is not measured by the scale. The net force is zero which is why the system is in equilibrium.
 
aloysious said:
That takes a lot of logic, doesn't it?. That was one of those liberal arts courses to avoid from what I heard.
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back in my day there was no "pre-law" curriculum......they suggested we take classes that required lots of reading and writing to prepare for law school.....to be completely honest I only graduated a double major......came up two classes short to complete a third major in philosophy.....
 
PostmodernProphet said:
back in my day there was no "pre-law" curriculum......they suggested we take classes that required lots of reading and writing to prepare for law school.....to be completely honest I only graduated a double major......came up two classes short to complete a third major in philosophy.....
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There was a student in my pre-med classes that had already graduated from Haverford with a degree in history. He aced all the minimum requirements to get into med school which was all he needed. 4.0. I was amazed that a history major could do that.
 
PostmodernProphet said:
no......hang a scale "upside down" and put a weight on the bottom it will still measure the weight........
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That's still one direction. And if you're hanging the scale secured from an immovable object, that object exerts an equal and opposite force.
@Mott. If the weight is stationary it's in equilibrium and the sum of the forces = zero.

If there is a force not equal to zero the object will accelerate until it reaches equilibrium.
 
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PostmodernProphet said:
the scale in the problem is not secured from an immovable object.......it is suspended in a loop between two movable objects......
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That is correct. But the two movable objects exert an equal and opposite force on each other causing the system to be in equilibrium. All objects are movable if enough force is exerted on the object. I'd assume there's no other force exerted on any of the objects and the pulleys are exactly equal.

You mention that scales don't necessarily measure in one direction. Let's assume this scale measures in two opposite directions, horizontally. Zero is marked in the middle and the string holding each weight is secured to each spring at the center (or at the ends, doesn't matter) . Obviously each spring would move in the direction of the weight, or force, until there was too much resistance in each spring. Eventually the weights would stop moving downward but each individual spring would measure the force which would be 100N.
So it really doesn't matter if the scale is measuring in one direction or two.
 
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aloysious said:
That is correct. But the two movable objects exert an equal and opposite force on each other causing the system to be in equilibrium. All objects are movable if enough force is exerted on the object. I'd assume there's no other force exerted on any of the objects and the pulleys are exactly equal.

You mention that scales don't necessarily measure in one direction. Let's assume this scale measures in two opposite directions, horizontally. Zero is marked in the middle and the string holding each weight is secured to each spring at the center (or at the ends, doesn't matter) . Obviously each spring would move in the direction of the weight, or force, until there was too much resistance in each spring. Eventually the weights would stop moving downward but each individual spring would measure the force which would be 100N.
So it really doesn't matter if the scale is measuring in one direction or two.
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Oh absolutely it does. If the scale has two movable ends (springs) attached to the meter than it would measure net force in both directions which would be 0 with two moving forces in opposite direction of equal force.

In this experiment you don’t have that. You have a scale with one stationary end and one movable end. Thus the scale only measures force applied on the movable end while the other force holds the stationary end stationary.
 
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