“If a projectile were deprived of the force of gravity, it would not be deflected toward the earth but would go off in a straight line into the heavens and do so with uniform motion, provided that the resistance of the air were removed.”
- January 4, 1643 – March 31, 1727
- Born in England (UK)
- Natural philosopher, mathematician, physicist, astronomer, theologian
- Proposed the laws of universal gravitation and motion, built the foundations of modern science, and systematized theories of natural philosophy and mathematics.
Quote
“If a projectile were deprived of the force of gravity, it would not be deflected toward the earth but would go off in a straight line into the heavens and do so with uniform motion, provided that the resistance of the air were removed.”
Explanation
In this quote, Isaac Newton is discussing the motion of a projectile (an object in motion) in the absence of gravity. He states that without the influence of gravity, a projectile would not curve toward the Earth but would instead continue in a straight line in its original direction. This is in accordance with his first law of motion, which states that an object in motion will continue in a straight line with uniform motion unless acted upon by an external force. In the absence of gravity (or any other forces), the projectile would maintain its motion indefinitely in a straight line.
Newton also notes that air resistance is another force that would typically affect the projectile’s motion. If this resistance were removed (assuming a vacuum), the projectile would continue in its motion without any deviation. The lack of air resistance would ensure that no force other than the initial velocity would alter its trajectory, meaning the object would travel in a uniform and straight path.
This principle is a direct application of Newton’s laws of motion, which formed the foundation for classical mechanics. Gravity, in this case, is the force that causes objects to be deflected toward the Earth and follow curved trajectories, such as the parabolic arc of a projectile. If gravity were removed, as in the scenario Newton describes, the only force acting on the projectile would be its initial velocity, and it would continue on a straight path. This concept would later become foundational in understanding orbital mechanics, as satellites or objects in space are not influenced by Earth’s gravity in the same way, leading them to follow predictable paths based on their initial motion.
In modern terms, Newton’s explanation foreshadows our understanding of inertial motion and the motion of objects in space. The absence of gravitational and other external forces means that objects will continue in straight lines with uniform motion. This principle is crucial in understanding not only projectile motion on Earth but also the behavior of planets, satellites, and other objects in space, where gravitational forces from different bodies determine their orbits.
