All Questions
335 questions
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Can you directly feel the effect of gravity, or only opposing forces?
I was trying to think through the consequences of Einstein's observation that a freely falling body does not experience its own weight. And, as freely falling (or "inertial") bodies will ...
17
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9
answers
3k
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In GR, what is Gravity? A force or curvature of spacetime?
GR starts with a principle called the Equivalence Principle, which states that gravity is indistinguishable from acceleration locally.
Here, what do we mean by gravity?
Case 1: Do we mean gravity as a ...
user247935
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1
answer
47
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Exploring Non-Rotational Artificial Gravity: Can Geometric Energy Fields Create Gravity-Like Effects?
I’ve been thinking a lot lately about ways to simulate artificial gravity in space without relying on rotational systems (like spinning habitats or stations). I'm curious if it's possible to create ...
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3
votes
2
answers
89
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Tug of war between observers in frames with different rate of time
You have a very dense hollow sphere of matter. Observer A is inside the sphere inside a rocket. Observer B is in an identical rocket outside the sphere where the ring's gravity is negligible. They are ...
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19
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How significant is the parabolic arch effected with an incline versus a decline in angle versus a decline in angle . For example throwing a dart
A dart players height can vary as can the height in which they raise their arm to aim.
Is there less parabolic arch when throwing at the same strength from above the target compared to below, due to ...
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1
answer
67
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When is it appropriate to say Newtonian gravity is a force? When is it not appropiate? [closed]
Please help me understand the notion of force when it is applied to Newtonian gravity. From my understanding forces in physics involve interactions with at least 2 objects and can cause an ...
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2
answers
118
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Why does a ball bounce back even when it is released and not thrown?
So according to my understanding when we thrown a ball towards ground we apply an additional amount of force which results in an acceleration greater than the one due to earth. When this ball reaches ...
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1
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102
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Aren't there only 3 fundamental forces? [duplicate]
I have heard that there are 4 fundamental forces: Gravity, Electromagnetism, the Strong Nuclear Force and the Weak Nuclear Force. But I have also heard that gravity is not a force at all, it is simply ...
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2
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63
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Why does hot air rise? Gravity based on density so electrons in higher shell further from nucleus have less gravitational force?
Are atoms with electrons in a higher state of energy, further away from the nucleus, effected less by gravity? What does electron distance from nucleus have to do with the force of gravity or higher ...
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1
answer
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Why does gravity act only towards the center of mass and not outwards [closed]
I would like to know why gravity is said to be concentrated towards the center of an object.the same is taught for any other force like centripetal force acting towards the centre in uniform circular ...
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1
answer
165
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If time moves slower the faster you go. Doesn't that mean that the gravity experienced will be lower too?
Disclaimer: I still don't understand the theory of general relativity. I'm completely ignorant.
I was watching the movie Interstellar yesterday and saw their interpretation of time dilation, I also ...
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22
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5
answers
6k
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Why does a plastic bag rip when it is raised to a higher position when being held but not when it is stationary?
Let me preface this as I am not a physics expert but this is something I was wondering as I would love a technical explaination.
For example: say a person is walking with a filled plastic grocery bag ...
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1
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2
answers
248
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Does a linearly accelerating spherically symmetric body emit gravitational waves
According to Birkhoff's Theorem, any spherically symmetric body will not emit gravitational waves. I can understand this for an object that is contracting and expanding because from far away the ...
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2
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132
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Gravity is not a Force? [duplicate]
I don't know much about this topic, but I read something saying that gravity is not a force using an example of inertial observation. I started thinking about the topic again when I was researching ...
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12
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1
answer
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Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced out?
While gravity is a force that attracts
objects with mass, dark energy (or, alternatively, the accelerated expansion of the universe) is not.
However, I have found numerous articles, forums, questions ...
- 2,878
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3
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121
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Gravitational potential energy of pendulum below pivot [closed]
The author wants to write potential energy of the ball attached to pendulum. He says that pivot is at $y=0$, so $y$ component is $-\ell\cos\vartheta$ so $U=-mg\ell\cos\vartheta$.
But why don't we ...
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1
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51
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2 Masses on a table confusion - Normal force and weight
Forces up are greater than forces down. However, the masses on the table obviously don't start flying upwards. Am I missing a force here?
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6
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1k
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How does general relativity theory explain gravitational pull? [duplicate]
I watched some videos on YouTube that explain why gravity is not a force,
according to general relativity theory.
I can wrap my head around the idea that spacetime can be curved due to a massive mass,
...
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3
answers
57
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Work energy and power [closed]
I saw this in a textbook and I want to confirm if it's true
If a body of mass m rolls down an
inclined plane of height h and length l (hypotenuse), the work done is mgh. It is the vertical height of ...
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1
answer
46
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Defining Free Fall: Does Gravity Need to be the Sole Force Present?
Can a scenario be considered free fall in physics if the work done by forces other than gravity is zero, but those forces are still present? Or is it necessary for gravity to be the only force present ...
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4
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2
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710
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General relativity when can we approximate to Newtonian gravity?
Lets consider this scenario in deep void of space where other curvatures of large objects are negligible in this case and we bring 2 objects lets say $A$ and $B$.
We give it a force slightly lower ...
- 441
2
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6
answers
834
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Is the gravitational force a phenomenon or a theoretical invention? [closed]
We use to say that gravitational force is a phenomenon. But since the theory of General Relativity replaced Newtonian gravitational force, how is it possible for a phenomenon to be replaced by a ...
1
vote
1
answer
163
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Do the other 3 fundamental forces also warp space-time?
I got this idea from Einstein's insight using the falling elevator. He says, that Gravity really cannot be distinguished from any other force accelerating the elevator.
A bunch of questions on here (...
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2
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475
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Why is gravity not a force? [duplicate]
Gravitation is the mutual attraction of masses, yet Einstein showed it is how spacetime is curved by mass and how mass moves in relation to this curvature. Why then do we still consider gravitation a &...
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4
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7k
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If gravity is not a force, then how come gravitational assists work?
I have learned about general relativity and how gravity arises from spacetime curvature. And I have always been taught that gravity is not a real force in the sense that
$$\frac{dp}{dt} = 0$$
And from ...
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1
answer
84
views
Does both the normal force, and the force of gravity apply in situations where they point in the same direction?
Imagine a loop, in a rollercoaster. When the car of some mass is at the top of the loop, the occupants would be pointing downwards.
At this point, in an ideal situation, the force of gravity would be ...
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votes
2
answers
415
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Confusion about near-identical terms: gravity, gravitation, gravitational force - are they all the same?
As my other questions also point out, I study this for fun. I am in no university yet.
as the title (hopefully summarizes), my question is this:
is these words(or terms,) the same?
gravity
...
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1
vote
1
answer
65
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Is hitting an obstacle half the size of my scooter wheel the same as hitting an obstacle half the size of my bike wheel?
I rode a scooter (the kind that you stand up and hold on to, with small wheels) and it didn't seem to handle bumps that would be minor if I was riding my bike. I was wondering if that is because ...
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4
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3
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488
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How does relativity explain Newton's apple? [duplicate]
You must have heard the anecdote about the apple falling on Newton's head that led him to come up with the concept of Gravity. A long time later, Einstein upgraded it to the General Theory of ...
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4
answers
124
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Einsteins gravity theory, but for static objects [duplicate]
https://www.youtube.com/watch?v=XRr1kaXKBsU this is a good video to explain Einsteins gravity.
The video claims that objects always move in a straight line, with an absence of a force of gravity, ...
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1
answer
64
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Aerostatic force experienced by object due to air
This is an undergrad physics problem, which puzzled me because of the little background provided; see also the comment below by @RC_23.
Problem.
Compute the force exercised by the air to an object ...
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0
answers
31
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Calculate uphill efficiency on different gears [closed]
I was interested to find whether it would be more efficient to climb a hill on a lower gear, so I did some calculations.
I have the following data of a custom vehicle:
Gear
Drive force (N)
Max speed (...
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1
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60
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Does the force that need to be applied to pull the weight out of a well by string is more at the start?
One way to estimate depth of the well is attaching a weight to a string then throwing it into the well until it touch a hard surface then pulling the string out of the well and evaluate its length.
...
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1
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1
answer
119
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A wind tunnel and 2 strong magnets in the wind tunnel creating a very strong field, how would the wind & magnetic force interact?
Sorry if I get some terminologies wrong I am not a physics major :)
If I had a big wind tunnel on earth blowing wind through a strong magnetic field (so the opposite poles of 2 giant magnets creating ...
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1
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How do you find the distance between a massive object and its certain gravitational force?
Okay so I know I might've not phrased the question very well so I will give an example to try to make sense of it:
Say we have the moon and a place in space where the moon's gravitational force is 1,...
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1
answer
14
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Required cushion/foam width to meet reduced force level in event of impact
Suppose a biker is riding a bike and bumps into roadside. If he/she is wearing good cushioned helmet, will not feel high 'g' force, but with an average helmet, impact can be high. So how does width or ...
4
votes
4
answers
941
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Where does gravity come from?
First, in my childhood, I learned that gravity is a force. Later, I learned that gravity is a property of spacetime. If gravity is a property of spacetime, then why is it one of the fundamental forces....
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1
answer
141
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If contact forces are repulsive then how are we able to pull stuff? [closed]
I searched a lot on internet(especially physics stackexchange) about the nature of contact forces. I came to know through most of them that it is repulsive in nature which surely means that your hand ...
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4
answers
2k
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Why does gravity seem to have two natures (force or warping of space and time)?
In classical mechanics, gravity is regarded as a force but in general relativity it's a warping of space and time in presence of mass. Are these two definitions the same? Or is this a duality nature ...
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1
answer
196
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How can the force between two charges change when the intervening medium is changed?
This is a common statement that the force between two charges changes when the intervening medium is changed however the gravitational force remains the same. But I have some problem with this.
When ...
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1
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65
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Why is gravity believed to have been as strong as the other fundamental forces at the beginning of the universe?
Why is gravity believed to have been as strong as the other fundamental forces at the beginning of the universe and what should be the cause of that possibility?
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2
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How big is the force just above the horizon of a black hole?
There are huge tidal forces at work around a black hole. But the larger the hole, the smaller the tidal effects near the horizon. So the differences between nearby local forces is small.
What about ...
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3
answers
3k
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Can tension force be negative?
Imagine we have a box (mass = 5kg) attached to a rope:
Considering gravity as $ 9.8m/s^2$, if we decelerate the box at $ 10.8m/s^2$, the tension force (of the rope) can be calculated like this:
$T = ...
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votes
2
answers
101
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Is gravity a force or not? - pendulum example [closed]
Let's imagine a pendulum and think about Newton's law about action and reaction: If gravity is not a force, what is the stress in thread balanced with?
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1
answer
147
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How do you find the angular velocity required to keep a constant distance $r_0$ between two unequal spherical masses?
I am having trouble coming up with this solution. Here is where I am at. I defined two variables, $r_1$ and $r_2$, where the former is the distance between $m_1$ and the center of mass, and the latter ...
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0
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63
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If there are no gravity under the general theory of relativity, how can we be attracted to massive objects (from the side)?
Watching this video, it is explained that there are no force of gravity under the general theory of relativity, but a force made by objects moving through spacetime.
The example made in this video to ...
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1
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0
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42
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What would happen in a hypothetical universe without the other forces other than gravity? [closed]
What would be the rules of a hypothetical universe where there is only gravitational force, and weak strong and EM force do not exist? What would be the consequences of that?
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3
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126
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Is gravitational time dilation considered as a repulsive force (from the point of view of a far-away observer)?
An infalling particle does never reach the event horizon of a Schwarzschild black hole, from the point of view of the reference frame of a far-away observer. Gravitational time dilation slows down its ...
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1
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Basic Gravity/Projectile Question
I have a really basic question before I start some code.
Can a projectile, launched into space, hit the opposite side of a planet with just its initial trajectory and force (assume an ideal, perfect ...
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1
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1
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67
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What will be the tension force in this case?
Suppose I have a block of mass $2\, {\rm kg}$ sitting on my table. Then I connect a string to it and pull it vertically upwards. The resultant acceleration is vertically upwards: $2.2\, {\rm ms}^{-2}$....
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