How Does a Wall Push Back with Equal Force?

[UrbanXrisis]

If a piece of fabric was stretched out, and I pushed my finger into the fabric with a force of 5N, the fabric will push back the 5N because of its potential energy. correct?

So what if I did the the same thing and pushed my finger agaist a wall? The wall doesn't stretch but it still pushs back with 5N. How does it know to puch back 5N on my finger?

 

[cdhotfire]

hmm, seems to me that if it didnt push back at 5 N it would either throw you back or you would break the wall.

 

[UrbanXrisis]

hahaha, I never knew I was that strong. Why does the fabric have to stretch to produce the 5N?

 

[Doc Al]

If a piece of fabric was stretched out, and I pushed my finger into the fabric with a force of 5N, the fabric will push back the 5N because of its potential energy. correct?

I assume you are asking: What is going on with the fabric that allows it to push with 5N of force? When you push the fabric, you are stretching the molecular bonds--like little springs--which resist that distortion.

So what if I did the the same thing and pushed my finger agaist a wall? The wall doesn't stretch but it still pushs back with 5N. How does it know to puch back 5N on my finger?

Ah, but the wall compresses. When you push on the wall, you are compressing those molecular "springs" that constitute the surface of the wall.

 

[Sirus]

Pretend it's a horizontal spring on a table. If you push on it (horizontally) with a constant force, it will be compressed, but eventually it will push back with enough force to keep your hand in equilibrium. This is because F_{spring}=-kx, where x is displacement from equilibrium position. I believe the fabric works the same.