B Force transition through spring

[Janez]

We put object on weight ang get a mass. What would that mass be if we put a spring between object and weigt, so that the spring woul shrink to half its original size?

 

[Doc Al]

We put object on weight ang get a mass.

Can you rephrase this? It's not clear what you are describing.

What would that mass be if we put a spring between object and weigt, so that the spring woul shrink to half its original size?

Again, your scenario is unclear. Are you placing a mass on a spring, so that the spring is compressed? The amount of compression depends on the stiffness of the spring (its spring constant) and the weight of the mass.

 

[Janez]

Thanx for answer.
Yes, the spreing compresess. For example we have a 1 kg object with no spring. How would we calculate the force when the spring is betwen object and weight?

 

[Doc Al]

How would we calculate the force when the spring is betwen object and weight?

You have something you call the "object" and something else you call the "weight". It's unclear what you are describing or what force you are asking about.

Can you give a simple diagram of what you are asking?

 

[berkeman]

What would that mass be if we put a spring between object and weigt,

Maybe you're asking this question: "Do I measure the same weight with a scale when there is a mass and a spring sitting next to each other on the scale, versus if I put the mass on top of the spring on the scale?"

Is that what you mean? I agree that a sketch would be helpful.

 

[Janez]

 

[berkeman]

How much does the spring weigh?

 

[Janez]

Nothing, for the purpuse of this question.

 

[berkeman]

Nothing, for the purpuse of this question.

Then the scale will measure the same weight in both cases. And in my example above, if the spring is also sitting next to the mass in your first drawing, then the scale will measure the combined weight of the spring and mass in both cases, regardless of whether the spring us under the mass or just sitting beside it on the scale.

Does that make sense?

 

[Janez]

So the spring transfer the whole force like solid object would? It does make sense, altought I found it somewhat unitnuiteve and I just wasnt sure.

 

[Doc Al]

So the spring transfer the whole force like solid object would?

Sure. Assuming equilibrium -- that the object isn't falling.

In fact, you can think of a solid object as if it were a spring -- place something on top of it and it will be compressed (perhaps only slightly), just like a spring.

 

[PeroK]

So the spring transfer the whole force like solid object would? It does make sense, altought I found it somewhat unitnuiteve and I just wasnt sure.

As the spring is not accelerating, the external forces on it must be balanced (Newton's second law). Therefore, the downward force of the mass on the spring (weight of mass) must be equal to the upward force the scale exerts on the spring. So, the scale shows the weight of the mass.

 

[Janez]

Ok, thanx for help.

 

[PeroK]

So the spring transfer the whole force like solid object would? It does make sense, altought I found it somewhat unitnuiteve and I just wasnt sure.

Or, imagine you were lying on the ground with a large spring on your chest. Would you allow an elephant to be lowered onto the spring? That might decide the issue!

 

[A.T.]

So the spring transfer the whole force like solid object would?

Yes, and there are no prefectly rigid objects, they are all "springs".

If the spring is assumed mass-less, then the net force on it must always be zero. So the force on the bottom must be equal but opposite to the force on top.