The laws of science will be tested once again at the Dignowity Hill Pushcart Derby, billed as a “collaborative artist intervention” that ? among other things ? presents creatively constructed pushcarts as positive symbols of change on San Antonio’s East Side. Organized by Tigercorn Productions (aka Cruz Ortiz and Mary Cantu), the seventh annual event includes 20-plus races starring “crazy ground-breaking scientific prototypes” to be judged in such categories as speed, audience favorite, and creativity in design. Guests are encouraged to bring lawn chairs, an umbrella for shade, plenty of water, and “the suegra y los kids.” For details ? including a pushcart plan designed by the Cub Scouts ? visit pushcartderby.com. Free to watch, $50 to participate (registration deadline is Thu, Mar 24), 2-5:15pm, Dignowity Hill Park, 700 Nolan, pushcartderby.com, contemporaryartmonth.com.