Universal Gravitation 4

4a) if gravity was much weaker , we can walk easier.
4b)if gravity was much stronger, we will walk hard and more difficult.
4c) if gravity was much was zero, we cannot walk on the ground.
Gravity or Gravitation is a property by which all objects attract each other. Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in many cases.
Gravitation is the reason for the very existence of the earth, the sun, and other celestial bodies; without it, matter would not have coalesced into these bodies and life as we know it would not exist. Gravitation is also responsible for keeping the earth and the other planets in their orbits around the sun, the moon in its orbit around the earth, for the formation of tides, and for various other natural phenomena that we observe.
Early (pre-Newtonian) history
Since the time of the Greek philosopher Aristotle in the 4th century BC, there have been many attempts to understand and explain gravity. Aristotle believed that there was no effect without a cause, and therefore no motion without a force. He hypothesized that everything tried to move towards their proper place in the crystalline spheres of the heavens, and that physical bodies fell toward the center of the Earth in proportion to their weight. Another example of an attempted explanation is that of the Indian astronomer Brahmagupta who, in 628 AD, wrote that "bodies fall towards the earth as it is in the nature of the earth to attract bodies, just as it is in the nature of water to flow".
Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th century and early 17th century. In his famous experiment dropping balls at the Tower of Pisa and later with careful measurements of balls rolling down inclines, Galileo showed that gravitation accelerates all objects at the same rate. This was a major departure from the Aristotle's belief that heavier objects are accelerated faster. (Galileo correctly postulated air resistance as the reason that lighter objects appear to fall more slowly.) Galileo's work set the stage for the formulation of Newton's theory of gravity.
Newton's theory of gravitation


Main article: Law of universal gravitation
In 1687, English mathematician Sir Isaac Newton published the famous Principia, which hypothesizes the inverse-square law of universal gravitation. In his own words, "I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centers about which they revolve; and thereby compared the force requisite to keep the Moon in her orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly." Most modern non-relativistic gravitational calculations are based on Newton's work.

if gravity was much weaker , we can jump higher