Reader feedback on Gravity. Key words: Gravitation, physics, physical science, force, Newton, Einstein, equivalence, relativity, quantum, black hole, escape velocity, Earth, Sun, Moon, orbit, Ron Kurtus, School for Champions Copyright © Restrictions
by Ron Kurtus
A total of 227 comments and questions have been sent in on Gravity. They are listed according to date. Also see Gravitation Feedback for questions on that topic.
List of the most recent 10 items
- How does gravity affect balloons?
- Distance for a falling bullet
- Tell 5 factors of gravity
- I think that the calculations are wrong
- How does gravity affect the human body?
- Is there a point in the Universe with zero gravitation?
- A force to counter gravity in aircraft flight
- Should use SI units
- Did Einstein discover gravity?
- I believe gravity is caused by centrifugal force
How does gravity affect balloons?
December 18, 2012
What effect does force of gravity have on an object like a balloon?
Richard - South Africa
If the balloon is not filled with air, it will fall to the ground the same as other objects. However, if it is filled with air, it will fall to the ground slower, because of air resistance on a light object.
If the balloon is filled with helium, it is lighter than air and it will float upward, overcoming the force of gravity. See How Objects Float in Fluids for information.
Distance for a falling bullet
April 10, 2012
I am a retired machine designer. I gave a friend a formula we used years ago figuring distance traveled by a falling abject for him to calculate bullet drop, thus:
Square number of seconds of bullet to target times 16.09
In checking myself I see that 16 is the correct figure. Where did I get 16.09 from? We used it all the time. I'm puzzled.
Jim - USA
The equation for the distance the bullet would fall is y = (gt^2)/2. Since g = 32.17 ft/s^2, the distance is 16.08 X the time squared. Rounding off to 16 is more reasonable, especially since air resistance has not been taken into effect.
See: Gravity Displacement Equations for Falling Objects and Effect of Gravity on Sideways Motion
Tell 5 factors of gravity
April 3, 2012
tell 5 factors of gravity ?
Momina - Pakistan
That is a rather vague question. Possible factors are that gravity:
* attracts objects toward the Earth
* accelerates objects at g = 9.8 m/s^2
* accelerates all objects at the same rate, independent of mass
* weight = g times mass
I think that the calculations are wrong
March 15, 2012
I think that the calculations are wrong if a meter is 3.3 feet then the 32.2 fps2 is wrong it should be 32.3631 and if you wanted to round up like they said they did then 32.3631 would be 32.4 not 32.2 so I was just wondering would that change the 9.8 newtons that g= in f=mg
Edward - USA
Actually, 1 m = 3.28 ft. See our English-to-Metric tool link on each page.
If we start with g = 9.807 m/s^2 from Overview of the Force of Gravity and multiply 9.807 X 3.28 = 32.167 ft/s^2. That rounds out to 32.2 ft/s^2.
How does gravity affect the human body?
February 26, 2012
I'm interested in how gravity affects the human body; standing erect, bending forward, leaning to one side. Are there equations for these angles relating to the gravitational force on the human body?
Gay - USA
Gravity pulls all the atoms in the body toward the ground. You can consider the human body a solid object with a center of gravity (CG) according to the orientation and configuration of the body. See Center of Gravity.
If a person was bending over, there would be a tendency of the body to tip over, rotating about the fixed point where the feet are on the ground. What happens is that your muscles change the angle slightly and stabilize the body to prevent it from falling over.
There are no real equations to use. It is mainly done by geometric drawings, similar to those in the lesson.
Is there a point in the Universe with zero gravitation?
February 22, 2012
In advance, Please forgive me for my spelling, grammer and rambling on.
Is there any such space in the known universe where there is zero gravity (meaning absolutely no gravitational pull or effect)all the time?
My understanding is that all MATTER has some form of gravitational pull. Also, all MATTER in the universe is in motion.
Therefore, is everything in the universe effected by gravity and have an effect on everything else?
Example; If a major star, planet or object was suddenly erased completely, would the entire universe be effected?
One theory I have is that the entire universe is like an "ecosystem". Meaning in some way it is all connected and self-dependant on everything in it. Any change will have some effect on the rest of it; big or small.
I feel this supports inteligent design. The Universe was Created and set in motion on purpose, and for a purpose. There can not possibly be this many "coincidences" coming so perfectly togeather.
I really would love and appreciate your views on this?
John - USA
If the Big Bang Theory that matter in the Universe exploded from some center point is correct, I would imagine that point could have zero net gravitational pull on it, since matter is probably equally distributed around that point.
A good way of thinking about it is like a form of ecosystem.
As far as supporting Intelligent Design, see Big Bang Theory and Religion.
A force to counter gravity in aircraft flight
February 9, 2012
I am looking at the principles of flight, particularly lift. Given the aircraft has thrust that contributes to lift in a climb, some of the weight is catered for by this thrust (other than aeodynamic - wing - lift). Now in straight and level flight the plane is effectively climbing (must have angle of attack). I am concerned, though I agree with the content here on gravity, that another force than lift exists to counteract gravity. With a plane we are talking not about a solid streamlined object, like a bullet, but something that has vertical wind resistance, which you will agree, changes the rate of descent. Also the plane has power constantly applied, unlike the bullet. With this powered forwards motion is the plane effectively seen to be lighter than it would be on the ground (ignoring inverse square law etc due to height above C of G)? It seems I am talking in the time domain, where a vehicle crossing a weak bridge at speed might get across, where at slow speed the bridge would collapse. Thanks for reading my question.
Michael - UK
Gravity can be considered a constant force toward the ground. For relatively short distances, it is straight down. But if the object is moving in a straight line. over a great distance, the curvature of the Earth must be taken into account. The inertia of the flying object make it want to go in a straight line, which is counter to gravity when the curvature is taken into consideration.
See Gravity and Newton's Cannon. As the cannonball moves faster, it will soon travel in a line into space. If the ball or object were continually propelled, the effect would be more dramatic.
Should use SI units
February 7, 2012
This is a great resource but it would be more useful in SI units since that's the standard for science nowadays.
Brendan - USA
Since so many non-scientific people in the U.S. still use the English system of measurement, I've tried to use both English and SI in all the Gravity lessons. Some example problems are in feet/sec, while others are in meters/sec.
However, in the Gravitation section, only the SI units are used.
Did Einstein discover gravity?
January 1, 2012
Albert Einstein discovered the effects that gravity had on the:
planets, stars and time its self. But if I'm right,he still
realised there was more to be learned about Gravity.
My question is, is this still true today?
I thank you in anticipation for you reply.
Wilfred - UK
Actually, Galileo did much of the early studies on gravity in the late 1500s. Then in the 1600s, British scientist Isaac Newton formulated the effects of gravity and gravitation on the planets and stars. Around 1900, Albert Einstein updated many of the laws or gravitation with his Theory of Relativity.
See Gravity and Gravitation for more information on the subject.
I believe gravity is caused by centrifugal force
December 11, 2011
The reason why gravity is not better understood is that Gravity is not a FORCE, but rather the EFFECT of the centrifugal force of Earth’s rotation pushing all the dark matter contained in the voids of space above our atmosphere being pushed away from the planet creating a space between the earth‘s crust and the outlying dark matter of outer space. If we had been born before this void was created, then we would have been flung beyond the atmosphere with the rest of the unattached matter. Thus the density of the earth’s crust keeps our atoms from being drawn to planet’s core. If we try to walk on water, we will be drawn further towards the earth’s core depending on our buoyancy. It is the presence of this SPACE devoid of dark matter that allows the earth’s core to impose the magnetic pull on the atoms of all other matter . It is the layer of dark matter that creates the envelope around our less denser atmospheric gasses. The matter that was created AFTER the centrifugal force of the planet’s rotation was established will continue to be drawn to the earth’s magnetic core as long as it’s rotation is strong enough to maintain the space between the plant’s crust and the dark matter that is waiting to be drawn to the earth’s core by it’s magnetic field. Why science insists on classifying Gravity as a FORCE I don’t understand. There seems to be enough evidence that it is NOT a FORCE, but the results of an effect of this type. If you want to indulge in an ANTI - GRAVITY environment, you’re going to have find the absolute North pole of the earth’s core and put together a device that will create enough of the same polar energy to push it away from the earth’s magnetic field. THAT is an ANTI-GRAVITY mechanism.
Dominick - USA
Gravity is gravitation near the Earth. You have to look into space and the attraction among planets, stars and galaxies in the study of gravitational forces.
Einstein states that gravitation is not a force between masses but instead is an effect of the curvature of space near objects of mass.
Also see Effect of Dark Matter and Dark Energy on Gravitation for more information on that subject.
Hopefully, this reader feedback has helped provide information about Gravity issues.
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