Lines will appear showing the straight line fit to the selected area. These lines are of the form
y=mx+b

where the value of y is determined based on the value of x. m represents the slope of the line, and b is the value of y when x = 0. In our case, the formula relates velocity to time:
v=mt+b

The slope, m, of these lines show how fast the velocity is changing in time.

1.) What could cause the velocity
to change?

In theory, the magnitudes of the slopes of these lines should be the same.

2.) What could cause them to be different? Can you adjust the track and repeat the experiment to see if you can make the magnitudes similar?