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by Ron Kurtus

A total of 78 comments and questions have been sent in on Gravity. They are listed according to date.

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List of next 10 letters




Gravity What is the gravity on earth USA
Gravity Want to calculate distance of a bullet shot straight up USA
Gravity A bullet goes though a window pane India
Gravity What are examples of negative work? India
Gravity Gravity and gluons Canada
Gravity Why do objects fall at the same rate? USA
Gravity Units of weight and mass USA
Gravity Is light affected by gravity? USA
Gravity Scale of earth to black hole velocity Australia
Gravity Does a piece of tissue and a ball fall at the same rate? USA

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First 10 letters

What is the gravity on earth

Topic: Gravity


January 6, 2011

what is the gravity on earth

William - USA



Gravity is a force that pulls things toward the Earth. The weight of an object equals the force. The acceleration of an object due to the force of gravity is at 32 ft per second squared or 9.8 m/s^2.

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Want to calculate distance of a bullet shot straight up

Topic: Gravity


November 18, 2010

How would you calculate the effects of gravity on a projectile traveling strait up at a known initial velocity. Say a bullet for example. How would you calculate how far it would travel before falling to earth.

Joe - USA



See the lesson "Gravity Distance Equations for Objects Projected Upward" at:

This lesson gives you equations for the distance the bullet would travel going up, how far to its maximum height, and the distance traveled on the way down. There are also some examples.

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A bullet goes though a window pane

Topic: Gravity


October 10, 2010

1. One light and another heavy masses are thrown vertically upwars
with same initial speed, which one will attain greatest height?

2. When a high speed bullet strikes a window pane it leaves a clean
hole in it where as a slow speed stone completely shatters it. Why?

Abdul - India



If there air resistance is not a factor, both the light and heavy objects will attain the same height. However, if air resistance slows down the lighter object, it will not attain the same height as the heavier object.

When an object hits a window pane, the glass first bends before it finally breaks. A high velocity bullet simply smashes through the glass, not giving it time to flex. But a rock will hit the window and start to bend it at the point of impact, until it finally breaks, as well as shatters. Of course, this happens very fast.

An example of something similar is cutting a tomato with a knife. If you chop down on the tomato with the knife, you will make a clean cut. But if you slowly press the knife on the tomato, it will give while you cut it and make a mess.

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What are examples of negative work?

Topic: Gravity


September 6, 2010

examples for nagative work

honey - India



The expression "negative work" can be misleading. It can mean work in a negative direction, or it can mean the opposite of doing work. Thus, the teacher needs to define clearly what is meant by the expression.

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Gravity and gluons

Topic: Gravity


August 19, 2010

If an object is falling towards the earth at an accelerated speed greater than the speed of gravity, does the force of the earth's gravity speed up it's acceleration or not? (I would say not, my reason being that gravity is in actual fact not an individual force, but the result of the force (gluon) that binds molecules together. This is why gravity is a constant no matter what the mass of the article is. I recently read that a Japanese Scientist who spent years trying to identify gravity, could not and concluded that gravity is not an identifiable matter.)

Jacob - Canada



Gravity is the force that moves objects toward the Earth. It does not have a speed. However, the force of gravity causes objects to accelerate at a constant rate.

The Quantum Theory of Gravitation says that the force is caused by graviton particles (not gluons, which hold the nucleus together).


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Why do objects fall at the same rate?

Topic: Gravity


June 22, 2010

Mr Kurtus:
My question is in the Physical Science portion. If you drop two unequal masses from a tower or a building, both the lighter and the heavier will hit the ground at the same time because gravity exerts an equal force on both masses ( ignoring air resistance) So says the literature.

Now take the same unequal masses and place them on a balanced beam at the same distance from the fulcrum and gravity seems to favor the heavier one, pulling it further down and unbalancing the beam. Please point out the flaw in my argument. On the surface, it does not seem to be intuitive. Thank you.

Aldo - USA



The force applied by gravity on an object is F = mg. That is also the weight of the object W = mg. Thus, if one mass is greater, the force (and weight) is greater, and the balanced beam scale will favor the heavier object.

However, the acceleration due to gravity "g" is a constant and is the same for both objects. It is independent of their masses. That means that both objects will fall and accelerate at the same rate.

This is also known as the Equivalence Principle of Gravity. See:

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Units of weight and mass

Topic: Gravity


June 18, 2010

If you 'weigh' 60 kg on Earth, you will 'weigh' 60 kg on the moon. Kilogram is a measure of mass and is measured on a balance beam. The scales at your local supermarket also use a balance beam to 'weight' in pounds mass. This is so a 10 lbm of sugar will read the same in Maine and in Florida.

Weight is a force and is usually measured in lbf or in newtons. Weight is measured on a spring scale. A man of 100 kg [220.46233 lbm] would weigh 221.036 lbf at the North Pole, 219.872 lbf at the equator, and 36.5 lbf on our Moon.

Russ - USA



Thanks for your comments.

A major problem with using the standard metric system is that kg mass and kg weight are often interchanged and confused. They are not the same, and using newtons for metric weight is preferred. I mention the difference and caution that must be taken in several articles.

I would not say that you "weigh" 60 kg. I feel it is much better to say that your mass is 60 kg, both on Earth and on the Moon. This would help eliminate any confusion.

Likewise, a pound-mass is 1/32 of a pound weight.

Measuring mass on a balance beam is something I hadn't thought of. I will have to add that to my material.

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Is light affected by gravity?

Topic: Gravity


June 10, 2010

Hi, nice site.
I have a few questions/possible lines of thought on gravity and energy.

1. Is pure energy affected by gravity? I say pure because any mass at all will be affected by gravity but pure energy is massless. It should not be affected by gravity.
2. Is magnetism affected by gravity? I am aware that to have magnetism you must have a mass that produces the magnetic effect. But is the actual magnetic force affected by gravity?
3. Is heat affected by gravity? Heat is energy and energy cannot be destroyed only converted. Heat rises on Earth and is radiated into space by the Sun. Heat dissipates, is that dissipation resulting from a gravitational constant that rips the heat signature apart or it it from another device.
4. Gravity is based on the mass of an object. In the edges of the Universe where matter has not yet traveled would gravity exist? If so, what does it pull on?
5. Is it safe to say that gravity is an energy? If it is a particle what keeps itself at a constant with itself.
6. In super-string theory, does gravity affect the strings?
7. Is it possible that the Universe is a vast bubble of gravity that has a leading edge like a balloon? All the matter in the Universe constraining from gravity and energy expanding from lack of gravity restraint.

Based on the idea that energy cannot be destroyed, only converted and matter is converted to more energy and gravity does not affect energy might the origin of the Universe from our point of view be as follows:

Unbeknown to us because we had not formed yet a parent Universe much older and bigger existed. This parent Universe converted all its matter to energy except one massively dense atom (particle). The particle gravitationally bound this Universe until inevitably it too converted to energy. At that point, Gravity itself no longer restrained anything and the energy burst forth in a massive pop (Like a pimple bursting). The resultant flow of energy started to cool and as it cooled it condensed into matter. Gravity then wrapped itself around the newly formed matter(mass) and as the mass grew so the gravitational bubble grew. As the energy cooled and converted in the parent Universe our new Universe became one with the prior Universe under the constraint of the gravitational constant. The Universe did not explode as much as it reformed bigger than it was. All new matter and mass but the same energy and gravitational (pressure) as you will.

As the Universe expands, continuing its cycle of conversion of energy gravity expands. Eventually this universe will convert all its matter to energy and the cycle will repeat.

Thank you for letting me rant. I am not a scientist but this makes sense to me. I understand that you may not agree with me but something I wrote may be interesting if nothing more that idle chatter.

I welcome your reply.

Just another part of the Universe trying to figure itself out.

Tom - USA



Gravitation is the attraction of objects of matter toward each other. Gravity is gravitation near the Earth.

You can consider gravitation as a force field between objects or, according to the Theory of Relativity, gravitation is a curvature of space-time.

Light or electromagnetic waves can be considered massless or pure energy. It has been shown that a ray of light is bent by gravitation. As far as I know, a magnetic field is not affected by gravitation. However, since electromagnetic waves are affected, it is possible that a magnetic field may also be affected by gravitation.

Heat is simply the rapid motion of molecules. Obviously, gravitation affects those molecules.

At the edges of the universe there are gravitational fields from the galaxies within the universe that are slowing the expansion of the universe.

It is quite possible that our universe is one of many other universes within what is called a multiverse.

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Scale of earth to black hole velocity

Topic: Gravity


June 7, 2010

I would to know what scale for new form black hole gravity on the scal like earth is 1 the is a 120 beetlejuice is 1300 what would the blackholes be?

by the way speed of does change becuase if it didn't it would excape it!

ben - Australia



A black hole has so much gravity that even light cannot escape. Since the escape velocity from Earth is about 11.2 km/s and the speed of light is about 300,000 km/s, you can see that the ratio is about 1/27000.


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Does a piece of tissue and a ball fall at the same rate?

Topic: Gravity


June 1, 2010

"Does a piece of tissue and a ball fall at the same rate?"

This seems to be onlly a partial question. My instinct was to ask where the ball and the tissue are located.

-Just didn't think it was a fair question without knowing if there's atomosphere whereever they are.

Chris - USA



If they were in a vacuum, like in outer space, they would fall at the same rate. However, air resistance will hold back the tissue from falling at the same rate. Also, air currents could even make the tissue fly upwards.

A good scientific question should include all variables and conditions. Unfortunately, often teachers and even textbooks state questions carelessly.

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