If you’ve ever sat underneath an apple tree and wondered why an apple fell down to the ground, instead of moving in any other direction, you would have had a similar experience that Isaac Newton had – more than 250 years ago. Gravity is a natural phenomenon which exhibits a force that allows matter to be attracted to other matter, enabling (for instance) an apple to fall to the ground. This might seem insignificant, but gravity is responsible for the current state of complexity of the universe. It caused the formation of planets and star systems, also resulting in the capacity for these to orbit. Gravity is also responsible for giving us weight on Earth – without it we wouldn’t be able to stand, walk, jump or run.
The famous astronomer, Galileo Galilei, first acted upon his observation of gravity. He developed a few of the first theories and equations of falling bodies. However, Isaac Newton took his research a step further, along with that of Johannes Kepler, to formulate the first general equation for the force of gravity. The equation states that the force of gravity is proportional to the mass of one object multiplied by the mass of another object, divided by the squared distance from their centers.
The next major addition to theories on gravity was made by Albert Einstein. His theory of “general relativity” described the effects of gravity as a result of curves in space-time, rather than force. He went on to propose that space-time is curved by matter, meaning free-falling objects would move along straight paths (known as geodesics) in curved space-time.
Gravity was also introduced into the field of quantum physics. This has caused the rise of theories stating that the attraction of matter is due to virtual particles called gravitons. However, these particles are yet to be observed. “Gravitational waves” have also been proposed, explaining how waves are formed when objects are accelerated by external forces.
Earth, along with every other planet in the universe, has its own gravitational field. The force of this gravitational field is explained by Newton’s equation for the universal force of gravity. However, the acceleration of free-falling objects within this gravitational field differs, which is dependent on many factors, such as the degree of elevation. It is generally accepted that the standard acceleration due to gravity on Earth (g) is approximately 9.8 m/s2, a value we often use during our A Level physics tuition classes, especially for the topic of Mechanics.