formula for Force, with displacement.?

Question

What formula would I use to determine force exerted by a rubberband when stretched a set length? All I know is the angle it is stretched and the distance.

Answer 1

F=kx, Hooke's law
x is its displacement form equilibrium. K is the spring constant or in this case the stiffness of the rubber band

Answer 2

F = kx from Hooke's, as said above, but beware...k is not a constant in rubber bands. k depends on x; so we really have is F(x) = k(x) x; where k(x) means the so-called constant is not constant as it varies with x. Thus, we have delF = k(delx) + delk x; where delk is the change in the k value over the stretch (delx) of the rubber band and delF is the change in force as the rubber band is stretched from x to X for example.

We know that k(x) and not k constant because in the extreme, as we stretch the rubber band close to its breaking point, at X, we can hardly stretch it farther. Thus, relatively k(X)>k(x) where X > x the stretch of the rubber band and X is close to its breaking point.