User suggestion: spring mass

[oliver-phet]

The masses and spring lab could use one improvement - an option to give the spring itself some mass as well using a slider. When you have the option of giving the spring mass (with a slider) it forces students to linearize, create a linear graph and use the slope and intercept, instead of doing individual calculations to determine the spring constant. The students would also be able to interpret the y intercept to find the mass of the spring. You could set the mass of the spring to zero for more basic classes.