Science Buddies: "Ask an Expert"

The link associated with how to find the spring constant value (k) for different rubber bands doesnt work. It takes me to some website that has no clickable links to find the article referenced. I also couldn't find the article anywhere else on google. I am not sure how I can find this k value so I can have my students do this as an energy transformation lab without having to go through hooke's law to find k.
Thanks!


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The activity can be viewed at: Rubber Bands for Energy

Hi - thanks for reporting this! We will update the project to remove the broken link. In the meantime you should be able to do this using two equations:

1) The energy conversion equation, PE = KE, 1/2*k*x^2 = 1/2*m*v^2

where k is the spring constant, x is the stretch length from neutral length, and v is the initial velocity of the rubber band.

2) The equation for the range of a projectile launched horizontally from a height of h:

d = v*sqrt(2h/g)

where v is the initial velocity of the projectile (equal to the velocity from equation 1), d is the horizontal distance traveled, and g = 9.81 m/s^2.

you can find that equation if you google "horizontal projectile range equation" (there is a more complicated version of the formula for non-zero launch angles, this is the simplified version when the launch angle equals 0).

Hope that helps, please write back if you have more questions!