Question

what two factors keep earth in orbit and around the sun and the moon in orbit around earth? a force and speed b mass and distance c gravity and inertia d gravity and distance

Explanation:

Gravity is the force of attraction between two objects. In the case of Earth - Sun and Earth - Moon systems, gravity pulls the Earth towards the Sun and the Moon towards the Earth. Inertia is the tendency of an object to resist changes in its state of motion. The Earth (and Moon) has a forward motion (tangential velocity) due to inertia. The balance between the gravitational pull (which tries to pull the Earth/Moon towards the central body - Sun/Earth) and inertia (which would make the Earth/Moon move in a straight - line path if there was no gravity) results in the orbital motion.

• Option A: Force is a very general term. While gravity (a type of force) is involved, speed is not the key factor in the sense of the fundamental physical concepts. The more relevant concept is inertia related to the motion.
• Option B: Mass and distance are factors in calculating the gravitational force (\(F = G\frac{Mm}{r^{2}}\), where \(M\) and \(m\) are masses and \(r\) is the distance). But they are not the two factors that directly explain the orbital motion. It is the combination of gravity (which depends on mass and distance) and inertia.
• Option D: Distance is a factor in gravitational force, but again, it is not the second factor along with gravity for orbital motion. The second factor is related to the motion of the object (inertia).

Answer:

C. gravity and inertia