Gravity

Gravity

If you’ve ever wondered why your back hurts after a long car ride, why we see phases of the moon, or how our earth stays intact the answer is that it has to do with gravity. When thinking of gravity, people often think of throwing a ball up and watching it fall. The idea that gravity is a force that brings objects “down” is a misconception. While gravity is the force that brings a basketball back down after a shot, it is, more specifically, the phenomenon that all objects with mass attract each other. The more mass an object has and the closer two objects are the stronger gravitational pull between them. When someone shoots a basketball it is attracted towards the center of the earth, and comes back down to the ground. In a system with two objects, both apply a force on each other. If a system contains a star and a pebble, the pebble still applies a gravitational force on the star, but the star moves so little that it is negligible. The forces are equal, but since the star is much more massive the acceleration induced by the force is small, so we don’t see it move.

  From: http://www.rri.wvu.edu/WebBook/Goetz/slides/figuresII/sld002.htm

When an object enters the gravitational pull of a relatively extremely massive object, the smaller object can orbit the larger one. An example of this is when an asteroid passes a nearby planet. It is possible the gravitational force towards the center of a planet alters the path of the asteroid so that it makes a full loop around the planet. As the distance between objects decreases the force of gravity becomes stronger. When the asteroid gets closer to the planet, the asteroid is attracted towards its center, and the result is that the asteroid orbits the planet. Although if the conditions are not right like the asteroid is moving too fast it will pass the planet. If the asteroid moves too slowly it will collide with the planet because the gravitational pull is too strong.

From: http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-causes-an-orbit.html

The force of gravity effects the weight we measure with a scale. Weight is the force of gravity acting upon a scale, while mass is determined by the amount of mass in one’s body. This means that if one were to weigh themselves on the moon they would weigh significantly less because the moon’s gravity is significantly less than the earth’s. The person’s mass would remain unchanged on the moon.

From: https://www.emaze.com/@AIZFQCI/Gravity-and-Motion

Galileo famously hypothesized that if one drops an object of different weights on earth the acceleration of gravity on them is the same. This shocked many people because the common belief was that weight determined how fast an object fell. Legend has it that Galileo went to the top of the leaning tower of Pisa and dropped two balls, one much larger than the other, and they fell at the same rate. The acceleration of gravity on earth is 9.8 meters per second squared. On earth every second the force of gravity acts upon something it applies an acceleration of about 10 meters per second. The reason a feather takes longer to fall is because the air on earth acts as a force against it. On the moon where there is no air the feather and the brick fall at the same rate.

From: http://lannyland.blogspot.com/2012/12/10-famous-thought-experiments-that-just.html

Like Galileo, Isaac Newton further revolutionized the idea of gravity. Isaac Newton was said to be sitting under a tree when he watched an apple fall. At this moment he had an epiphany, that what causes an apple to fall from a tree, and the moon to orbit the earth is the same force. This was revolutionary because Newton introduced the idea that some physical laws that apply to us on earth apply across the universe. Newton’s theories were progressive, but later revised 250 years later by Albert Einstein. Isaac Newton believed that gravitational effects occurred instantly, and if the sun were to vaporize the earth would immediately stop its orbit around the sun. Einstein disproved this notion after his study his light. Einstein found that light acts as cosmic speed limit, and gravity does not take effect instantaneously. He hypothesized that if the sun were to vaporize, it would take eight seconds for any change in gravitational effects on the earth to occur. It is eight seconds because that is the time it takes for light to reach the earth from the sun.

Gravity is a unique property of our universe. The attraction between objects with mass shapes our universe into what it is today. This law causes orbits, the formation of planets and stars, ocean tides, and many more phenomenon we witness every day.