Let’s talk about physics! Wait, bear with me. Don’t roll your eyes at me; I promise you this will be interesting and if you are good, there may be bacon. A BBC Two video has recently been making the rounds again on social media and it is possibly one of the more interesting theories in physics that seems to boggle many minds because it just doesn’t seem like it could be right. It is a theory that seems to be counterintuitive. In the western world pre-16th century, it was generally believed by scholars that the acceleration of a body was directly proportional to the weight of said object. (Basically, a 10 kg object will accelerate 10x faster than one that is 1 kg.) Aristotle even included this theory in his book on mechanics and this was the norm of thinking until good old Galileo.

Galileo Galilei (1564-1642), astronomer, mathematician, philosopher, dropper of objects big and small, and all around heretic to the Catholic Church, made pioneering observations with far-reaching implications to the world of physics. He earned the title of “the Father of Modern Science” with his theories and the mathematics to back these theories up. How many people can boast to be the topic of conversation and have much of their work remain relevant four centuries after their death?

The theory in particular that we want to look at here is where Galileo proposed that two falling bodies of differing mass would fall at the same rate when falling in a vacuum without the interference of air resistance and/or inertia. He was attributed to dropping objects of varying weights off the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their weight. This story has been retold so many times that it has become a legend of discovery (much as the falling apple is to Newton) but probably did not happen. Most historians believe that this was probably more of a thought experiment than a factual occurrence. Of the studies that he did on falling objects, many were carried out using an inclined plane where both issues of timing and air resistance were much reduced.

This is the theory of free fall; any motion of a body where gravity is the only force acting upon it. An object in free fall experiences acceleration due to gravity. So, gravity is a constant. Well, sort of. Like many things in science gravity is prone to some variation. Okay, maybe not so constant.

Most know that the moon’s gravity is less than the Earth’s; about a sixth of it. This enabled the astronauts wearing full kit (space suit plus life support backpacks) of approximately 300 pounds the ability to hop around like rabbits without much effort while on the surface of the moon. Jupiter has some crazy gravity; the most intense in the Solar System at 24.79 m/s2. It has the strength to affect every planet in one way or another and has been known to capture moons and tear apart asteroids. In the 1990’s Jupiter’s gravity tore apart Comet Shoemaker-Levy 9 before it crashed spectacularly into the planet.

Furthermore, gravity varies from location to location on the Earth itself. Gravity is greater at the poles than at the equator; greater at sea level than at the top of the Himalayas. There can also be differences at various locations due to the geology of the area. For arguments’ sake though g= 9.8 m/s2 (meters per second squared) is the generally accepted value of gravity here on Earth.

So try this little experiment. Take a piece of paper and a pencil. Hold them at the same height and drop them simultaneously. The acceleration of the pencil is greater than that of the paper which floats and drifts on its way down. A small thing called air resistance (AKA: aerodynamic drag) is getting in the way here. How would we reduce the drag so the race to the ground would be more even? Take the piece of paper and crumple it up into the tightest wad you can make and try the experiment again. Now, when you release the two they should hit the ground at approximately the same time because the tight wad of paper has less surface area to be affected by air resistance.

How would you reduce the air resistance even more? The only way to do this is to perform this experiment in a vacuum. Under these conditions a feather and a bowling ball would hit the ground at the exact same time. Nowhere else was this better illustrated than when astronaut David Scott released a rock hammer and a feather at the same time while on the surface of the moon during the Apollo 15 mission in 1971. That is until Brian Cox and BBC succeeded with the help of NASA in their Space Power Facility in Ohio while filming the Human Universe. Take a look at the video here: https://www.youtube.com/watch?v=E43-CfukEgs

I would love to duplicate this experiment but NASA has failed to answer my request to use their big vacuum thingy and it seemed like a long drive to Ohio. I will have to be satisfied with my “experiments” of dropping various articles in the lab to do my own testing, much to the chagrin of my colleagues. It is best not to drop heavy books behind someone who is pipetting chemicals into specimen bottles. Congratulations! you have made it to the end of this blog about physics and your head and/or mine did not explode but I am sorry to say I have no bacon for you. I am now off to wreak havoc. Maybe I will see if my boss will let me build a Tesla coil.

–Janice Willson

For more physics information please take a look here: https://physics.info/falling/  He/she does a good job with explaining things without making you fall asleep.

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