How does gravitational strength vary on different planets?

Gravitational strength indeed varies depending on a planet's mass and radius, making this the correct choice. This variation can be explained through the universal law of gravitation, which states that the gravitational force between two objects depends directly on their masses and inversely on the square of the distance between their centers.

In simpler terms, a planet with a larger mass will exert a stronger gravitational pull due to its greater mass. Conversely, the radius or size of the planet also plays a crucial role; if a planet has a large mass but a large radius, the gravitational strength experienced at its surface may be less compared to a smaller planet with the same mass because the gravitational pull weakens with distance.

Therefore, gravitational strength is not uniform across the universe or even among celestial bodies in a single solar system. For example, Earth, which has a significant mass and reasonable radius, has a gravity of about 9.81 m/s², while a smaller planet like Mars has a weaker gravitational pull due to its lower mass and size.

This understanding underscores the significant factors of mass and radius in determining gravitational strength, confirming why this choice is accurate and relevant.