Normal force reading on a scale -- How and why?

[Elvis 123456789]

Homework Statement

let's say you have a regular bathroom scale, which we know measures the normal force that it exerts on a person aka. apparent weight. Now let's say that we didn't know that it measured the normal force when a object was on it. Obviously we still know that the only two forces acting on the object are the normal force and the force of gravity. We also cannot perform any experiments with the scale, such as accelerating it to see if the scale reading changes. Do you have enough information to deduce that the scale reads the normal force and why? ( This wasn't really a homework question, just a misunderstanding that I've had with this topic, and i wanted to see if somebody can help clear it up for me)

Homework Equations

The Attempt at a Solution

 

[J Hann]

What does Newton's 3'd Law say and what is the definition of the normal force?

 

[Elvis 123456789]

What does Newton's 3'd Law say and what is the definition of the normal force?

Newton's 3rd Law states that in every interaction there are equal and opposite force pairs that act on different objects. The normal force is the force that a surface applies perpendicularly to the surface on an object. I don't see how either of those two things will give me the answer to the question.

 

[J Hann]

Isn't the normal force considered to be the "normal reaction" of the scale?
What else can the scale reading be?

 

[Mustafa Mahfouz]

i still don't get it , could u please explain more ? and some pictures would really help

 

[jbriggs444]

Obviously we still know that the only two forces acting on the object are the normal force and the force of gravity.

We do not know this. Because it is obviously false. There is a third force.

 

[Chestermiller]

We do not know this. Because it is obviously false. There is a third force.

I'm having trouble figuring out the third force you are referring to. Please tell me you are not talking about air buoyancy.

 

[jbriggs444]

I'm having trouble figuring out the third force you are referring to. Please tell me you are not talking about air buoyancy.

The two forces already identified are the normal force (acting on the top of the scale) and gravity (acting on the bulk of the scale). What holds it up?

The idea that "gravity" acts on the top of the scale would be incorrect. Your feet act on the top of the scale, not gravity.

 

[Chestermiller]

The two forces already identified are the normal force (acting on the top of the scale) and gravity (acting on the bulk of the scale). What holds it up?

The idea that "gravity" acts on the top of the scale would be incorrect. Your feet act on the top of the scale, not gravity.

I thought the OP was referring to the forces acting on the object.

 

[jbriggs444]

I thought the OP was referring to the forces acting on the object.

Right, you are.

We are concerned with what the scale is measuring. So forces acting on the scale are naturally the relevant things to consider.