All Questions
Tagged with newtonian-gravity conventions
93
questions
0
votes
3
answers
47
views
Is gravitational potential energy of body by $mgh$ negative? [closed]
Consider a 15kg object at 1m from earth ground level,
is P.E = 15kg * 9.8m/s^2 * 1m = 147J
or P.E = -Gm1m2/r^2 * h = -9.8 * 15kg * 1m= -147J
after browsing for a while on debate of potential energy's ...
-1
votes
1
answer
65
views
How Can there be a Gravitational Potential when there is NO Gravitational Field? [closed]
How does it make any logic that there exist a potential when there is no net field
for example when we have a Hollow Sphere with mass we can find out the the gravitational *potential inside the sphere ...
1
vote
4
answers
75
views
Why is work done by force $+mgh$ in the situation of throwing something up?
If there is a particle at point A(at rest) and a force moves it to point B(Above point A vertically)(final velocity = 0 at this point), the work done by gravity is $-mgh$. This I understand as the ...
- 85
2
votes
4
answers
187
views
Is the gravitational potential energy of an object on the ground 0? [duplicate]
In class, we were reviewing kinetic and potential energy and my teacher claimed that on the ground, objects have potential energy. However, as they cannot fall further, isn't their gravitational ...
- 539
0
votes
0
answers
62
views
Why does Newtonian gravity necessarily imply that gravitational potential energy is negative? [duplicate]
Why can't the zero value of gravitational potential energy be set at a different point instead of infinite distance within Newtonian gravity?
I am not asking why is gravitational potential energy ...
- 476
1
vote
2
answers
103
views
Defintion of gravitational potential
I am not much clear regarding the defintion of "gravitational potential":
Is the work done for bringing the unit mass from infinity to that point by, gravitaional force or external force? (...
1
vote
3
answers
94
views
Gravitational Potential Energy Behavior [duplicate]
I had a question regarding gravitational potential energy and escape velocity. I don't really understand the concept of escape velocity. I have been learning it as the velocity required for an object ...
- 19
-1
votes
2
answers
222
views
Derivation of the gravitation potential energy and gravitation potential
I have some slight confusing in deriving the gravitation potential energy.
In the image below, it explains that the gravitation potential energy is equal to the work done from infinity to a distance r ...
1
vote
5
answers
246
views
Work done in raising an object to a height
When we raise an object to a height $h$, it is said that the potential energy of the object is increased by $mgh$. But isn't the work done by gravitational force $-mgh$?
Then that will essentially ...
- 702
1
vote
2
answers
80
views
Confusion in definition of Potential Energy
Potential energy is defined like this. $ΔP.E=-W_{AB}$. This means that the potential energy at point A minus potential energy at point B should equal the negative of the work done by a conservative ...
- 122
0
votes
1
answer
75
views
What is the significance of a reference point in calculating the potential?
The gravitational potential is given as $$U(r)=-\frac{GMm}{R}$$ where $G$ is the universal gravitational constant $M$ is the mass of the earth and $m$ is the mass of an arbitrary object and $R$ is the ...
- 335
0
votes
1
answer
47
views
What happens if we define the gravitational potential zero point at a finite distance? [duplicate]
Two questions.
Can we, and if so how do we define the gravitational potential of a mass (say the sun) to be zero at a finite distance (say 1 light year)?
How does this change the gravitational force ...
- 47
4
votes
3
answers
1k
views
Work done by the force of gravity
My question is very similiar to this one: Work done by gravity on falling object does not seem to equal change in mechanical energy
As I've understood it, work is only done on an object if the object ...
- 71
0
votes
1
answer
68
views
Kepler's Two-Body Problem Choice of Sign
I have been going over the solution to Kepler's problem and there is a subtlety I am missing. The notes I am following (my own notes from a while ago in fact...) get to the following expression
$$
\...
2
votes
3
answers
224
views
Why gravitational constant $G$ does not have the factor of $4π$?
We know that electrostatic constant $K=\frac{1}{4\pi\epsilon}$.
This $4\pi$ came from the surface area of the surface in which charge is enclosed.
Then, why don't gravitational constant has the factor ...
- 21
1
vote
2
answers
169
views
Gravitational potential energy of a two body system from infinity
In determining gravitational energy of a two body system,we define it as the negative work done by gravitational force in bringing those two bodies from infinity to a distance $r$ with respect to the ...
- 19
0
votes
4
answers
124
views
Is it correct to say, any object has a huge amount of potential energy?
Let's say if it is a $ 1 kg $ metal ball.
Now if we consider it together with a planet some 500 light years away (or if we consider Neptune), then there is potential energy between this metal ball ...
- 332
0
votes
3
answers
160
views
Potential energy $= -GMm/r$ then how could potential energy ever be positive? [duplicate]
Using the $U = -GMm/r$ where $r$ is a distance which would be positive how could potential energy ever be positive?
How could it be positive according to the equation $mgh$?
- 83
-2
votes
3
answers
1k
views
Why is the total energy of a satellite negative?
I have learnt that the total energy of a satellite is negative because it is in a bounded system(closed system). Total energy of a satellite is defined as: $$\text{T.E.} = \text{K.E. + P.E.}$$ and ...
- 452
1
vote
4
answers
311
views
Concept of Gravitational potential energy
Change in Potential energy corresponding to a conservative force is defined as $$\Delta U = U_f - U_i=-W_f$$ and gravitational potential energy is $$\Delta U = U_f-U_i = -W_g $$ Suppose a mass $m_1$ ...
- 452
0
votes
1
answer
34
views
Confused between potential energies
Let us suppose an object of mass $m$ has been raised $h$ meter above. From definition of gravitational potential energy, the potential energy of the ball should be $-\frac{GMm}{R+h}$. But now let us ...
- 1,179
0
votes
2
answers
298
views
What is the meaning of Gravitational Potential when multiple point masses are involved?
According to Wikipedia "The gravitational potential $V$ at a distance $x$ from a point mass of mass $M$ can be defined as the work $W$ that needs to be done by an external agent to bring a unit ...
- 379
0
votes
1
answer
182
views
Better understanding of the definition of Gravitational Potential as the improper integral $\frac{1}{m}\int^x _{\infty}G\frac{Mm}{x^2}dx$
According to Wikipedia "The gravitational potential $V$ at a distance $x$ from a point mass of mass $M$ can be defined as the work $W$ that needs to be done by an external agent to bring a unit ...
- 379
3
votes
3
answers
941
views
What is meant by 'Gravitational Potential Energy of a System'?
'Gravitational potential energy' is defined as: 'energy an object possesses because of its position in a gravitational field'.
Consider two planets of masses $M$ and $m$ at a distance from $r$ of each ...
- 2,578
1
vote
2
answers
1k
views
Work done to bring a mass from an infinite distance away
In the notes I received from high school teacher, it says:
How much work is done by the gravitational field of the planet in bringing a satellite from an infinite distance to a position $r$ away?
In ...
- 372
2
votes
5
answers
612
views
Gravitational potential energy at $r = \infty$
At $r = \infty$, the gravitational potential energy of an object due to Earth’s gravitational field is at a maximum value of $0$. I understood this to mean that an object will have maximum potential ...
- 372
0
votes
2
answers
876
views
Why there is a negative sign on the gravitation formula?
It all started when I was coding some simulation of the Newton's Law of Gravitation and Culomb's Law.
When I was seeking information on the internet, I found out that some people wrote this formulas ...
- 1,525
0
votes
1
answer
451
views
Find the density of the sphere, $\rho(r)$
If the field vector $\hat{g}$ is independent of the radial distance withing the sphere, find the function describing the density $\rho$ of the sphere, $\rho(r)$.
In spherical coordinates, the ...
- 273
-1
votes
1
answer
35
views
Potential energy in the gravitational field - Why is $r_2$ striving against infinity?
why is $r_2$ striving against infinity in the formula $𝑊 = 𝐺𝑚𝑀(\frac{1}{𝑟_1}−\frac{1}{𝑟_2})$, so its often simplified to $𝑊 = \frac{𝐺𝑚𝑀}{r}$ ?
I know that in the final formula, r is the ...
2
votes
2
answers
116
views
Why not make GPE positive?
I was teaching a student about negative GPE with the formula:
$$U=-\frac{GMm}{r}$$
He wasn't very happy with why it was negative and came up with this formula instead:
$$U'=-\frac{GMm}{r}+Bm$$
where $...
- 2,356
1
vote
2
answers
298
views
What is the height in the potential energy formulation? [duplicate]
Most examples I've seen describe the (gravitational) potential energy e.g. with an example of a ball thrown upwards, and explain how the sum of the ball's kinetic and potential energy is constant at ...
- 13
6
votes
4
answers
2k
views
Why is gravity considered a negative vector in a pendulum question?
In many places and tutorials, gravity is often considered as a negative vector.
I am confused as to why is that? I though I was missing something from trigonometry but it was just negative in first ...
- 171
1
vote
1
answer
97
views
Gravitational potential energy sign
Following is a small derivation just so I can explain my question. The gravitational potential energy is:
$$(*)U_g = -\frac{GMm}{r}$$
And:
$$ \Delta U =-GMm(\frac{1}{r_{final}} - \frac{1}{r_{initial}})...
- 1,038
0
votes
1
answer
341
views
How can we choose any level for gravitational potential energy to be zero?
In my book, I read that we can choose any level as Zero Gravitational P.E. and measure height of objects above it and call its energy 'mgh'. But by saying that all the points on that level is of zero ...
- 5
6
votes
1
answer
185
views
Why is the constant in Coulomb's law written in terms of $\pi$ but not the constant in Gravitation?
What is the significance of writing it as $\frac{1}{4\pi \epsilon _0}$? Why not just name the whole thing $\epsilon _0$? And if there is a significance, why not do the same thing for gravitation?
I ...
- 6,355
0
votes
1
answer
1k
views
Reference Point and Change in Potential Energy
Okay so I am VERY confused. Everything online is telling me that I can choose any reference point for potential being zero and still get a consistent result for potential difference HOWEVER I have ...
- 43
0
votes
1
answer
54
views
Can we make uniformity in marking zero potential? Say it at earths surface or at infinity from earths surface?
The gravitational potential energy at infinity os supposed to be zero. Since body always moves towards lower potential, the gravitational potential is taken as negative so that gravitational potential ...
- 111
1
vote
2
answers
166
views
Why isn't the work done by gravity positive in this situation?
I want to find the work done by the force of gravity to move an object of mass $m$ from infinity to a point $P$ at distance $r_p$ from a body of mass $M$ (that I assume fixed). The formula should be
\...
- 113
3
votes
3
answers
125
views
What is wrong with this calculation of work done by an agent bringing a unit mass from infinity into a gravitational field? [duplicate]
Let us assume that a gravitational field is created by a mass $M$. An agent is bringing a unit mass from $\infty$ to distance $r < \infty$, both measured from mass $M$.
The agent is always forcing ...
- 49
0
votes
3
answers
988
views
Why is the gravitational potential energy defined as negative? [duplicate]
It is said that since work is done by the gravitational potential itself , so at a finite distance the gravitational potential energy of the body is negative.
Could someone explain why?
0
votes
4
answers
1k
views
If Gravitational potential energy increase with height then why it is 0 at infinity?
Due to MGH relation, if we increase height then potential energy increases. Then why it is zero at infinity?
0
votes
2
answers
119
views
Sign Problem When Dealing With Quadratic Air Resistance and Gravity [closed]
While dealing with an object falling vertically, and subject to quadratic air resistance, an equation of motion that is often presented is
\begin{equation*}
m\dot{v} =mg-cv^{2}
\end{equation*}
In ...
- 15
-1
votes
2
answers
321
views
The reference point of potential energy
In one dimension (I am not familiar with multivariable calculus), potential energy is defined as
$$E_p = -\int F \ dx$$
This is an indefinite integral, and the integration constant $C$ is involved ...
- 485
0
votes
5
answers
1k
views
What is the reason for work done by gravitational force being negative?
When a body is moved from $r=∞$ to say, $r=R$, work done by the gravitational force is $-(GMm)/R$.
Why is it negative even though the Force and the displacement of the body is in the same direction. ...
- 72
0
votes
3
answers
352
views
Sign of gravitational acceleration
The gravitational potential energy comes from the formula $mgh$ where $g$ is always $>0$.
But when we get to choose it's sign? I figured out, it really depends on what you choose as positive axis ...
- 101
0
votes
1
answer
6k
views
Relationship between gravitational potential and gravitational field strength
So I was trying to think of a reasonable relationship between gravitational potential and gravitational field strength. However, I'm not sure whether this is correct:
$g=\frac{GM}{r^2}$ where $g$ is ...
- 117
0
votes
2
answers
332
views
Reason for the negative sign in the gravitational potential $-GM/r$? [duplicate]
why the gravitational potential comes out to be negative that is $-GM/r$?
where G is gravitational constant
M is mass of the body
r is position at which the mass has to be brought from infinity.
- 21
6
votes
5
answers
7k
views
Why the gravitational potential energy at infinity is zero?
If an object is taken from earth's surface to infinity, it's gravitational potential energy becomes zero (always taken as zero), but it doesn't make any sense as energy can never be destroyed so where ...
- 356
0
votes
3
answers
127
views
Why am I getting a negative sign in this derivation?
I want to derive a formula for calculating the final velocity of an object that falls from rest as it reaches the surface of the Earth. I want to take the change in acceleration into account and hence ...
- 1,329
0
votes
2
answers
589
views
If an object in free-fall is moving upward, the object's velocity is decreasing. Does this mean that the acceleration is -9.8 m/s/s?
I have a problem (that I am not asking you to solve) where it takes $4s$ for an object to travel upward to its maximum height, and we have to determine how far the object travelled. If the ...
- 129