SNHS Physics Blog 2: Isaac Newton and His Apple

Aira Dani

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One day, 4 centuries ago, Isaac Newton was pondering upon life, when, out of nowhere, an apple hit him on the head. This epiphanic moment led him to his discovery of the laws of motion. Well, that’s what they want you to believe.

What really happened was similar to our situation today. A bubonic plague had hit town and Newton was forced to move to his childhood home to continue his studies safely. While he was looking out his window, he saw an apple fall to the ground and asked himself why the apple fell straight down instead of up and why it moved at a 270 degree angle rather than just float in mid air.

Conducting experiments and making observations led him to his breakthrough where he claimed “every body in the universe is attracted to every other body with a force that is inversely proportional to the square of the distance between them,” which he called the gravitational force. This answered his question about why the apple didn’t move at an angle, thus creating the second law of motion- the law of acceleration. Since the moment the apple left the tree, it was accelerating toward the ground. Despite this development, he still contemplated its vertical motion.

Soon, he came to the conclusion that after the apple dropped from the tree, it only experiences one force, the force of gravity. He proved this with continued experiments of a ball dropping as well as the apple tree itself. This allowed him to fully develop his first law, the law of inertia- every object will stay in rest unless acted upon by an outside force. When the ball lost its connection to the tree, the ball was in freefall: the only force acting on it at that point was gravity, which is what caused it to drop to the ground. Since the gravitational force is exerted by the center of the Earth, it pulls all things toward it, causing them to appear as we see them, on the ground. If there had been an intervening force, such as a person catching the apple, the apple would then exert a force on the person’s hand and since the hand would apply a force in the opposite direction, greater than the force of gravity, it would be able to slow down (and eventually stop) fall of the apple.