What would happen if you dropped a 1kg ball and a 10kg ball at the same time from a high building? Most people would think that the 10kg ball would obviously fall faster and thus hit the ground faster, but the truth is they would fall at exactly the same time. The reason for this is that the force that accelerates a falling object is gravity, which on Earth is constant at 9.81ms-2. This means that no matter how heavy the object is, they will always accelerate by 9.81 metres per second per second. This was hypothesised by Galileo Galilei, who came up with the thought experiment of dropping two balls of different mass from the Leaning Tower of Pisa (there is debate as to whether he actually performed the experiment). The theory was later solidified by a certain Isaac Newton, who devised the laws of universal gravitation and the three laws of motion.
However, if the two balls were dropped from an extremely high place, they may land at different times as mass affects the terminal velocity – when the force of gravity equals the force of drag caused by air resistance, leading to a constant velocity. A heavier object will keep accelerating to a greater velocity than a lighter object, which would have reached terminal velocity before the heavier object.
One place where this will not happen is in a vacuum where there is no drag force. To prove that the hypothesis that two objects of different masses will fall at the same time in the absence of air resistance, Commander David Scott of the Apollo 15 moon mission took a hammer and a feather with him. Once he landed on the moon, he dropped the hammer and feather in front of a live camera, showing that the two landed at exactly the same time. He thus proved that Galileo’s conclusion from two hundred years ago was in fact correct.
A professor stood before his philosophy class and had some items in front of him. When the class began, he silently picked up a very large and empty jar and proceeded to fill it with golf balls. He then asked the students if the jar was full. They agreed that it was.
The professor then picked up a box of pebbles and poured them into the jar. He shook the jar lightly. The pebbles rolled into the open areas between the golf balls. He then asked the students again if the jar was full. They agreed it was.
The professor next picked up a box of sand and poured it into the jar. Of course, the sand filled up everything else. He asked once more if the jar was full. The students responded with a unanimous “yes.”
The professor then produced two cups of coffeefrom under the table and poured the entire contents into the jar effectively filling the empty space between the sand. The students laughed.
“Now,” said the professor as the laughter subsided, “I want you to recognize that this jar represents your life. The golf balls are the important things – your family, your children, your health, your friends and your favourite passions – and if everything else was lost and only they remained, your life would still be full.
The pebbles are the other things that matter like your job, your house and your car.
The sand is everything else – the small stuff.”
“If you put the sand into the jar first,” he continued, “there is no room for the pebbles or the golf balls. The same goes for life. If you spend all your time and energy on the small stuff you will never have room for the things that are important to you.
Pay attention to the things that are critical to your happiness. Play with your children. Take time to get medical checkups. Take your spouse out to dinner. Play another 18 holes. There will always be time to clean the house and fix the disposal. Take care of the golf balls first – the things that really matter. Set your priorities. The rest is just sand.”
One of the students raised her hand and inquired what the coffee represented. The professor smiled. “I’m glad you asked. It just goes to show you that no matter how full your life may seem, there’s always room for a couple of cups of coffee with a friend.”