Link to the MassSpring app on iTunes
The MassSpring app is a basic physics lab, in which a block is attached to an ideal spring. You can set the mass of the block, the spring constant of the spring, and the initial position of the block. The block is released from rest from that initial position, and then oscillates back and forth horizontally on a frictionless surface. This motion is an example of what we call simple harmonic motion. The spring is at its natural length when the block is at a position of x = 0, so nothing happens if you release it from there!
Here is a worksheet, in PDF format, to accompany the app.
Worksheet for the MassSpring app
You can use as you work with the app to understand the physics of simple harmonic motion. The worksheet has a collection of equations you can apply as you experiment with the app, and it has suggestions of various activities to do to help you understand how the block and spring system works.
Using this app, you can explore various graphs to help you understand what is going on. First, there is a set of three bar graphs that show the block's kinetic energy (KE), the elastic potential energy (PE) that is stored in the spring, and the total energy (the sum of the kinetic and potential energies). There are also three other graphs – you choose which of these three graphs to display by pressing the appropriate graph button. Graph 1 (see above) shows the block's position, velocity, and acceleration, all as a function of time. Below, we can see the effect of increasing the mass of the block by a factor of 4.
Graph 2 (see below) shows the kinetic energy, potential energy, and total energy, all as a function of time.
To go from the picture above to the picture below, the spring constant was increased by a factor of 4.
Graph 3 (below) shows the kinetic energy, potential energy, and total energy, all as a function of the position of the block.
Understanding the different graphical representations can give you various insights into the basic physics of a simple harmonic motion system, as well as into how and why we use graphical representations in the first place.
With no friction and no air resistance, this is an idealized system, and you might want to think about what would happen if we were able to add some friction. Idealized systems like this can be a good starting point, though, for getting an overview of how things work.
By the way, if you are an educator or a student who can't afford the 99 cents it costs to buy the app, drop me a line at Prof.Duffy at gmail.com. I should be able to get codes for 50 free downloads from Apple and, assuming I have some left, I'll send you a code for a free download.
This web page was first posted on September 23, 2009.
Last update: October 2, 2009.
Note: this app was submitted to the app store on September 20, 2009, and approved for sale on September 30, 2009.