Screen Summary Tweak: Add idea of a track

[terracoda]

Like in Gravity Force Lab Basics, I want to add the idea that the mass spheres move a long a track to match the qualitative position information provided in aria-live alerts and aria-value-text.

Change Paragraph 2 of Screen Summary
OLD version of P2:

• The Play Area has a blue sphere labeled m1 and a red sphere labeled m2. A force vector arrow starts at the center of each sphere and points directly at the opposite sphere. Spheres can be moved closer or farther from one another. The mass of each sphere can be increased or decreased. Each sphere is held in place by a robot.

NEW version with changes highlighted in bold:

• The Play Area has two mass spheres, a blue sphere labeled m1 and a red sphere labeled m2. A force vector arrow starts at the center of each sphere and points directly at the opposite sphere. Spheres can be moved closer or further from one another along a track. The mass of each sphere can be increased or decreased. Each sphere is held in place by a robot.

[terracoda]

@zepumph, I took care of this one, so closing.