I looked up a few answers and found that spring means stiffness and resistance and that string means elastic and slack but both can mean tension. I understand what those words mean but not in this context. can someone give a good visual example? my original question was the difference between a slingshot with a string vs one with a string of your curious
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For springs I think of Hook’s Law. It has a stable length and it has a resistive force when pushed or pulled which is proportional to the length that is is compressed or stretched. This force acts to restore the stable length and often leads to oscillatory motion.
A string can’t be compressed — you can’t push a string. So it’s just something that you pull. As long as the force is not so strong as to break the string, then it’s a way of transferring where the force is applied. From a physics perspective, it makes me think of pulleys.
A string gets stretched. That stretching creates a force called tension (which, at a microscopic level, is the result of the molecules in the string being pulled out of their lowest-energy positions). Tension tends to pull the string back to its original length, which creates a pull *toward* the string on both of its attachment points. For example, if an object is hanging from a string, its weight *mg* is pulling downward, while the tension T in the string is pulling upward. You can also think of this as the string *transmitting* the force holding it up at the top to the object it’s holding up at the bottom, though this can run into trouble if the tension is changing over time or if the string is deforming in response to the forces on it.
Compressing a string doesn’t do anything – a string in this context is usually assumed not to offer any resistance to compression, since the spring easily buckles out of the way. (You can think of a string as a spring that only resists stretching.)
A spring gets compressed *or* stretched. That compression creates a force (which can be a tension force if it’s being stretched, or a compressive force if it’s being squeezed) that resists the push or pull on the spring. If it’s being compressed, the force pushes outward, and if it’s being stretched, the force pulls inward. For an idealized spring and small enough amounts of force, it turns out that the force obeys an equation called [Hooke’s law](https://en.wikipedia.org/wiki/Hooke%27s_law). Hooke’s law says that the force applied by a spring is proportional to how far out of position it’s been compressed or stretched (F = k*x, where F is the force, k is some unknown constant that depends on the material you’re using, and x is how far you’ve stretched). A spring that has been compressed or stretched by 2 inches will apply twice the force of that same spring stretched by 1 inch.
Finally, the *stiffness* of a spring is the constant *k* in that Hooke’s law equation. It describes how much force it takes to compress or stretch the spring. A stiffer spring takes more force to compress (larger *k*, which makes the resisting force *F* on the other side of the equation bigger).
(And finally finally, remember that these are just approximations that are valid for typical materials under normal conditions. They can and do fail outside of those assumptions!)
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