B Why Does a Spring Return to Its Original Position After Being Stretched?

[tellmesomething]

Consider a spring in its natural length. I start pulling the string and the force i apply increase from 0 to 5, while this happens theres a restoring force wanting to be back in its original position(intermolecular force) and i am able to stretch the string until this spring force or restoring force equals to my applied force. Now when i remove my hand why does it go back to its original position, i understand the reaction force is opposite in direction to my applied force and at the point where the extension stops the net force on the string is 0. But when i remove my hand does the external force vanish? Its still there right shouldnt the spring still be in equilibrium?

 

[Dale]

Your hand is the source of the applied force. Why would the applied force remain after its source leaves?

 

[tellmesomething]

Your hand is the source of the applied force. Why would the applied force remain after its source leaves?

when i push an object on a frictionless surface i dont remain in contact i merely give it a push and it continues moving until hit by an obstacle. can it not be similar to this?

 

[Dale]

when i push an object on a frictionless surface i dont remain in contact i merely give it a push and it continues moving

It doesn’t require a force to move in a straight line at a constant speed. That is Newton’s 1st law. When you stop pushing then the force stops in this case too.

 

[Lnewqban]

Consider a spring in its natural length. I start pulling the string and the force i apply increase from 0 to 5, while this happens theres a restoring force wanting to be back in its original position(intermolecular force) and i am able to stretch the string until this spring force or restoring force equals to my applied force.

The force that you apply deforms the crystals that form the metal.
The reactive force is directly proportional to that deformation, which is elastic (until certain point).

Now when i remove my hand why does it go back to its original position, i understand the reaction force is opposite in direction to my applied force and at the point where the extension stops the net force on the string is 0.

When you remove your hand, the force that was deforming the metal disappears, and the crystals naturally go back to the original position.

But when i remove my hand does the external force vanish? Its still there right shouldnt the spring still be in equilibrium?

Yes, the external force suddenly disappears, which breaks the previous equilibrium of hand-elastic forces.
The elastic force makes the spring return to its original length, while its magnitude goes from 5 to 0.

 

[hutchphd]

when i push an object on a frictionless surface i dont remain in contact i merely give it a push and it continues moving until hit by an obstacle. can it not be similar to this?

This is not how the world works. You are in good company: Aristotle made the same wrong assumption. It was shown incorrect by Isaac Newton

 

[A.T.]

when i push an object on a frictionless surface i dont remain in contact i merely give it a push and it continues moving until hit by an obstacle. can it not be similar to this?

When you stop pushing an object on a frictionless surface, the net force goes to zero, so the object moves at constant speed.

But when you stop pulling at the streched spring, the net force on most spring parts is not zero, because the internal restoring forces are a function of the current deformation, not of the current external forces.

 

[tellmesomething]

This is not how the world works. You are in good company: Aristotle made the same wrong assumption. It was shown incorrect by Isaac Newton

this was possibly the dumbest question i asked on here, at that time i had just started learning physics and had very wrong intuition/assumptions lol, i mean i was literally calling the "restoring force" reaction force as if action and reaction forces act on the same body . i also thought velocity only exists if acceleration does, good heavens

 

[A.T.]

at that time i had just started learning physics

I didn't check the OP date when replying. Glad to see you made so much progress since then.

 

[tellmesomething]

I didn't check the OP date when replying. Glad to see you made so much progress since then.

I obviously still have a long way to go to become like yourself and others on this site, but thanks