What two sources of friction do you have to overcome when you are walking?

What are atoms of the same element with varying number of neutrons

What is a possible result of higher air temperature caused by global warming

The sun’s mass is 2.0×10^ 30 kg, its radius is 7.0×10 5 km, and it has a rotational period of approximately 28 days. if the sun should collapse into a white dwarf of radius 3.5×10 3 km, what would its period be if no mass were ejected and a sphere of uniform density can model the sun both before and after?