Kevin has edited encyclopedias, taught history, and has an MA in Islamic law/finance. He has since founded his own financial advice firm, Newton Analytical.
Universal gravitation is the link that keeps the universe from falling in on itself. In this lesson, we see how it works and discuss how to use the formula of universal gravitation to find out differing weights.
The Gravity of All Things
If you've been studying physics for long, then you're probably familiar with gravity. In fact, if you've spent any time wondering why you couldn't dunk a basketball in middle school to impress your teammates, you've spent some time thinking about gravity. After all, gravity is the force that holds us to the Earth. However, it probably wasn't until you got to middle school science class that you learned that the Earth is held in position around the sun by gravity. Your teacher may have brushed it off, saying something about how big things exert gravity on smaller things.
Well, your teacher was only half right. It turns out that every object that has mass in the universe exerts gravity on every other object in the universe regardless of size. Now before you start waxing on poetically about how everything is connected, most of those forces are so small as to not really have an impact on anything else. However, they are worth noting. This idea of everything exerting gravity on everything else is called universal gravitation.
What Does Universal Gravitation Mean?
Okay, so what does all this talk about universal gravitation mean? Ever want to go to space? Or maybe watch satellite TV? Universal gravitation is the phenomenon that keeps the universe from disintegrating. Without it, even if the Earth was the only body in the universe that exerted gravity, space capsules and satellites would have to journey far away to stay in orbit. Instead, they reach a sort of zero point between the gravity of the Earth and the gravity of some other large structures, like the sun.
So why do we even bother with universal gravitation? In short, because of Newton's law of equal and opposite forces, we can figure out how to overcome the Earth's gravity by using the universal gravitation formula.
That formula is: the force of gravity is equal to the product of the gravitational constant times the masses of each object, then divided by the square of the distance between the centers of gravity of each object. That's a lot to take in, so normally it is abbreviated as:
F(grav) = (G x m1 x m2) / d^2
G, or the universal gravitation constant on earth, is 6.67 x 10^-11. If that's not an odd enough number, then the unit on it certainly is: Newtons meters squared divided by kilograms squared. So why the odd unit? When everything follows through, that is the unit that leaves the math with Newtons, which is the unit of force.
Over the next few minutes we'll calculate the universal gravitation of various objects towards each other.
For this experiment, you will need the following: a mass balance, a 500 g mass object, a 1000 g mass object, a 250 g mass object.
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Start by taking the mass of each object to ascertain that you have the exact mass. Record those using the universal gravitational formula: F(grav) = (G x m1 x m2) / d^2. Calculate the universal gravitation between the objects at the following intervals to complete the chart below.
As a part of your analysis section, discuss the following questions:
How did universal gravitation change as a result of masses being altered?
How did universal gravitation change as a result of distances being altered?
Okay, at this point you may want to pause the lesson while you run through those calculations. Here's a chart that shows the answers that you should have come up with. So what does this all mean? The universal gravitation between the masses in our experiment was the greatest when the 250 gram object was closer to the 1000 gram object. The force of universal gravitation was higher because the masses were larger and the ions were closer. It decreased dramatically when the distance was increased. Likewise, it decreased as the mass of the items decreased.
In this lesson, we applied the concept of universal gravitation, which states that all objects that have mass exert gravitational force on every other object in the universe.
Thanks to the universal gravitation formula, we know that force of gravity is equal to the product of the gravitational constant times the masses of each object, then divided by the square of the distance between the centers of gravity of each object.
F(grav) = (G x m1 x m2) / d^2
This formula tells us that universal gravitation is inversely proportional to distance as the bigger the distance gets, the smaller this force becomes and that mass matters. To see how that works, we compared the universal gravitation of a set of objects with respect to each other at varying distances.
By using the formula, we saw that the objects in question had a greater attractive force when objects were closer and larger, and a much smaller one when they were smaller and further away.
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