Email of the Day 01/25/11 Earth’s Gravity

From: Terry 
Sent: Monday, January 24, 2011 10:29 PM
Subject: gravity

OK, this might sound dumb but,why do we have gravity here on earth? is it the mass of the earth holding us down or is it the rotation of the earth that’s holding us down? or both? Terry


The Earth’s mass creates the force we call gravity. It’s a force still not totally understood.

One fact:  Mass alters time, our GPS system relies on time to calculate where you are on earth.

If the system didn’t  make corrections for time differences between the GPS satellite ring and the earth’s surface, it wouldn’t have enough accuracy for most things..

If you had a twin brother who lived his live at 10,000 feet elevation, he’d become a different age than you living at sea level.

A mass will also bend light, we can see light from beyond our sun, and measure the bending effect of the Sun’s mass.  keep this separate from a magnetic field, that’s another amazing thing, and I put a page up about this. There is so much misinformation about our magnetic field. Fact is…we’d have no atmosphere here on earth wihtout it….all would be blown into space by the solar winds (particles).

There are now some fairly good TV programs about our solar system that discuss some of these things. A great book to read is “A history of time” Stephen Hawkings, a permanent book for the shelf.  Bottom line?  Gravity is relative to mass,  go to the moon, and you don’t weigh as much. If you take a 100 pound weight to the moon, and put it on an accurate scale, the number of pounds it weighed would reveal the weight of the moon relative to the mass of the earth as a percentage.

Got something to add or correct, please do!

George B.

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16 Responses to Email of the Day 01/25/11 Earth’s Gravity

  1. Quinn says:

    The equation for gravitational force is:

    F = G * (M1 * M2)/R^2

    F is the gravitational force
    G is Earth’s gravitational constant, 9.8 meters/second ^2
    R is the radius or distance between the two masses, M1 and M2

    From the equation you can see that the gravitational force is proportional to the mass of the two objects in question. And the closer they are to each other, the greater the mutual gravitational force. So the earth’s gravity pulls on you just as much as your gravitational force pulls on the earth.

    I’ve always thought that must have something to do with why some of us tend to “gravitate” toward big heavy old engines.

  2. George B. says:

    And now some might ask: If light is bent by a gravitational field, can we measure the amount of bending, calculate the mass that caused the bending and approximate the mass of the light? Can we also measure the difference in time at two points within a gravitional field and calculate the mass of time?

    • Quinn says:

      The gravitational lensing effect has to do with the distortion of space-time rather than a direct effect of gravity on light itself. Light is carried in packets of energy called photons that are massless. Thus, gravity does not act on them directly.

  3. Jack Alan says:

    Gravity is a tough one. Nearly all of our understanding is naturally based upon observation that objects of mass and matter APPEAR to be attracted to each other.

    Some physicists attempt to explain that is just a convenient way to look at things, but the actual mechanism is more like inertia, and looks a lot like a more sophisticated version of what we sometimes call “centrifugal force”. The theory is with the “big bang”, all matter originated at the singularity, and is hurtling outwards from this center thourgh space. The natural tendency is to follow a “straight line”. (This is just a concept please…). But matter apparently “warps space” and makes the track that hurtling masses take deviate from that straight line. (This warpage has been observed in bending of light that while should travel “straight” actually has to follow the fabric of space.) This deviation from the natural path during this continuous expansion of the universe creates the appearance of what we call “force of gravity”. Though in this case it is not actually a force.

    The analogy would be something like riding in an automobile around a long sweeping curve. The APPEARANCE is that the door of the car is pulling you towards it. Discovery! It is a new gravity! But no, you are aware it is what you call centrifugal force. Of course in reality it is not a force at all, it is YOUR physical resistance to being redirected from the straight line you were traveling along before the car started to follow the curve. Everything in the car seems to be “pulled” towards the side of the car. But it is inertia.

    Some theory says that gravity actually has a lot in common with centrifugal force, in that it is a manifestation of inertia effects on the scale of the universe. As all matter has effects on warping space, all of the interactive effects by matter and mass create the appearance of a system of forces of gravity.

    That is one outlook anyway.

  4. Lendusaquid says:

    You are all wrong. There is no such thing as gravity, the Earth sucks!

    • George B. says:

      I think you have been studying the ‘ass end’ of the planet too long, pull your nose out of the middle east, and get back to shoveling snow..
      BTW, good to hear from you…

  5. Greg says:

    Gravity varies all over the earth even at the same elevation. In fact it is measured with gravity meters. is a manufacturer of these.

    What amazes me is that the earths rotation doesn’t have a more noticeable effect on gravity from the pole visa-vis the equator.

    • John says:

      Interesting thought about the pole vs equator! Calculating centrifugal force on a given mass, at a given radius, and given rotational speed must be a straight forward calculation for an engineer. A spring scale, string, assorted weights, and a watch no doubt were experimented with by inquiring minds hundreds of years ago. How much LESS does this calculation say a person, for instance, will weigh at the equator vs at the pole?

    • George B. says:

      I’ve been thinking about this post Greg.. and then noted that Prof Mueller at UC Berkley put up a Gravity map in his class, in his case, it was of an area with a huge impact crater that had been filled with sediments of far less dense materials than those that souround the crater..

  6. Richard says:

    wow how do you not understand gravity. It is attraction of one mass to another. Measure each mass and the distance between each other

    from above.
    F = G * (M1 * M2)/R^2

    F is the gravitational force
    G is Earth’s gravitational constant, 9.8 meters/second ^2
    R is the radius or distance between the two masses, M1 and M2
    what we don’t understand is the mechanism for gravity but though experiment after experiment we have understood how it works and what it does.

    how else could we make the above formula and it’s right all the time except for very small things. Quantum mechanics. I won’t go there.

    the force trying to throw us off the planet is very very small. We are going too slow.
    mass doesn’t alter time speed does. and yes the gps system allows for this in their time calculations.

    again yes we can figure out the mass of a proton but it is nothing just the energy it has in is only because of it’s speed. It has a trivially amount of mass but we cannot measure it. Since stopping it to measure it destroys it, we have to measure it in indirect ways. Also for its time, it does not exist. It’s traveling at the speed of light. Something again hard for us to understand.

    • George B. says:

      Quoting you “mass doesn’t alter time speed does.” I’m not so sure everyone agrees. Mass bends light, and many believe that mass actually warps the fabric of time. But.. I’m certainly NOT holding a class on the topic, but I am >STILL< reading "the history of time", a favorite book..

  7. George B. says:

    Now… for a far tougher problem to solve…

    Why are Americans so dumb they allow the whores in Washinton DC to continue putting our social security pauments into the General Fund from which they rob as they choose? It’s really far dumber that suggestign the world is flat!

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