What must two objects have in order for gravitational force to act on them?

Why does earth rotate? because earth is formed from cold gases collapsing due to gravity because the matter in the nebula that formed earth was spinning because earth forms more than 99% of the mass of the solar system because the hydrogen atoms inside the nebula fused to form helium

What is the energy in joules of a mole of photons associated with visible light of wavelength 486 nm?

Jenny places a strip of ph paper into a solution. when she removes the ph paper, it has turned yellow-green. what should jenny do next to determine the ph of her solution? a. use a different testing method because the ph paper should not change colors b. place the ph paper into a machine that reads the ph of the solution c. compare the ph paper's color with the color of ph paper from another solution d. compare the ph paper's color with a chart of colors and ph ranges