Final answer:
Gravity varies from planet to planet because it depends on the mass and radius of each planet, affecting the acceleration due to gravity and consequently the weight of objects.
Step-by-step explanation:
The acceleration due to gravity varies from planet to planet because it is influenced by the mass and radius of each planet. For instance, on Earth, the acceleration due to gravity is approximately 9.80 m/s², giving a 1.0-kg mass a weight of 9.8 N. However, on the Moon, gravity is much weaker, with an acceleration of only 1.625 m/s², resulting in the same mass having a weight of about 1.7 N. This change in gravity and therefore weight is due to the fact that the force of gravity is contingent upon the product of the masses involved and inversely proportional to the square of the distance between their centers, according to Newton's law of universal gravitation. The Moon's smaller mass and slightly different radius compared to Earth's result in a weaker gravitational pull.