What happens when a substance undergoes a physical change?

You are about to open a container of soy milk but notice that there are instructions to “shake well before serving.” the soy milk is most likely a

Aperson walks first at a constant speed of 4.89 m/s along a straight line from point a to point b and then back along the line from b to a at a constant speed of 2.95 m/s. what is the average speed over the entire trip?

What does si stand for, when referring to a system of measurement