What other step do they need to add to their experimental design in order to determine the effect of mass on the speed of the toy cart?

I don't know

i think the answer is gold im not entirely sure

he movement of air through earth's or any planet's atmosphere is called wind, and the main cause of earth's winds is uneven heating by the sun. this uneven heating causes changes of atmospheric pressure, and winds blow from regions with high pressure to those with low pressure.

i hope this : )