What makes March 19th the first day of spring?

If an athlete runs once around a track, back to the starting line, her average velocity is zero. true or false?

It is reasonable to assume that the bulk modulus of blood is about the same as that of water (2.2 gpa). as one goes deeper and deeper in the ocean, the pressure increases by 10000 pa for every meter below the surface. if a diver goes down 80.0 m in the ocean, by how much does each cubic centimeter of her blood change in volume? give the answer in cubic centimeters (actually one cubic centimeter equals one milliliter).

Mixing salt in water is an example of physical change