Which force causes all objects with mass to attract one another? A. Compression
B. Electrical force
C. Magnetic force
D. Gravity

Astone weighing 1.5 kilograms is resting on a rock at a height of 20 meters above the ground. the stone rolls down 10 meters and comes to rest on a patch of moss. the gravitational potential energy of the stone on the moss is joules.

In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. what is the electron's orbital frequency? what is the effective current of the electron?

What is the role of the water cycle in maintaining freshwater levels in lake and rivers?