What is standard unit? Why is it necessary?

Earth's atmosphere is composed of mostly two gases. name the two gases that make up the majority of the atmosphere and use the pie chart to tell the percentages of each.

1which body contains the majority of the mass in the solar system earth jupiter the moon the sun 2 what keeps the objects in the solar system such as planets orbiting around the sun the force of gravity the galaxy exerts on all objects within it including the solar system the great distance between the sun and the planets the sun's nuclear fusion which acts on each object the gravitational force between the sun and each object in the solar system

Based on this activity, is kinetic energy always transformed into potential energy?