Why do springs go back to the opposite direction they were pulled in?
In: Physics
There are two types of springs, a compressive spring and a extension spring. One is designed to push back into shape when squashed, the other retract when pulled.
For the extension spring, the recoiling or more the springs ability to pull itself back to its original shape, is caused by molecular properties of the metal. This property is known as the tensile strength.
So think of using a spring and pulling it outward as a tug of war between spring vs. human.
When you pull on a extension spring it will ‘grow’ in size and appear to get longer. Imagine you are pulling more of the tug rope across the centre line.
If the pull force doesnt overcome the springs tensile strength, the spring wins and doesn’t change shape and pulls itself back over the tug of war centre line – the spring wins.
If however the pull force of the human does overcome the springs tensile strength, the molecular structure of the spring is fractured beyond repair. Imagine you’ve injured the spring. The spring can’t go back to its original starting position on it’s own accord, it requires external force to put it back together.
This is why springs go back in the opposite direction to where they were pulled – or more why they return to their original shape.
the potential energy of the spring is increased when you pull it back. PE = 1/2*kx^2. This gets transferred to kinetic energy with the spring flinging forward and when the spring is back to its original position, the potential energy is again 0, but kinetic energy is max. Then when it keeps extending, the potential energy again increases and kinetic decreases and it goes forever.
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