# gravity

### I Is free fall NOT the same as floating in space?

For many, many years (don't ask), I've been running into the classic example of the local reference frame: the man in the box who can't tell if...
Thread by: James Demers, Apr 24, 2018, 2 replies, in forum: General Physics

### B Relationship between mass and acceleration

Hi. I am currently working on an assessed science experiment write-up. The experiment is about whether or not if mass of a pendulum bob affect the...
Thread by: Anthony Lu, Apr 22, 2018, 9 replies, in forum: General Physics

### I Why do objects with mass attract each other?

In most cases, we know why things happen. Protons can stick with each other because of the strong nuclear force. There's all kinds of forces and...
Thread by: Yan_Dalton, Apr 19, 2018, 1 replies, in forum: Classical Physics

### B Force of gravity along the radial direction

I am trying to work out the velocity of the ball in a loop in terms of theta from the horizontal (like a unit circle) as it loses contact with the...
Thread by: Pochen Liu, Apr 19, 2018, 8 replies, in forum: General Physics

### A When does the Minkowski metric get non-zero off-diagonals?

I have only seen scenarios so far where the elements are all along the diagonal, but what are some known cases where there are off-diagonal...
Thread by: DuckAmuck, Apr 16, 2018, 15 replies, in forum: Special and General Relativity

### Insights Either the Sun Is Getting Smaller or Gravity Is Getting Weaker

Greg Bernhardt submitted a new PF Insights post Either the Sun Is Getting Smaller or Gravity Is Getting Weaker [ATTACH] Continue reading the...
Thread by: klotza, Apr 8, 2018, 17 replies, in forum: Astronomy and Astrophysics

### Artificial gravity on a ship without the whole ship rotating

I know that rotation can cause there to be artificial gravity. But I was thinking of making a floor plan that is all horizontal with the...
Thread by: caters, Mar 31, 2018, 11 replies, in forum: Science Fiction and Fantasy Media

### Having trouble working out centripetal force?

1. The problem statement, all variables and given/known data The Russian Mir space station had a mass of 130 tonnes and orbited Earth at an...
Thread by: Jan Berkhout, Mar 24, 2018, 4 replies, in forum: Introductory Physics Homework

### Bead on a string, find y(x) if horizontal velocity is const.

1. The problem statement, all variables and given/known data [ATTACH] 2. Relevant equations K = (1/2)mv2 U = mgh W=Fd Integration/Calculus 3. The...
Thread by: Phantoful, Mar 22, 2018, 2 replies, in forum: Introductory Physics Homework

### Apparent (clearly false) contradiction - Kepler's Third Law

1. The problem statement, all variables and given/known data When considering a satellite in geosynchronous orbit, its speed is zero across...
Thread by: Brad, Mar 19, 2018, 2 replies, in forum: Introductory Physics Homework

### B Gravity and human population, Solved?

The next questions will be in english and spanish, since my birth language is spanish I may be mistaken in a few english words....
Thread by: David Prince, Mar 17, 2018, 13 replies, in forum: General Physics

### I How can General Relativity explain the Moon drifting apart from Earth

According to various sources, the Moon is separating from Earth 4 cm every year. I’ve searched for the explanation and I’ve found the following:...
Thread by: DLeuPel, Mar 3, 2018, 6 replies, in forum: Special and General Relativity

### B Would it be possible to make something float?

While waiting in the doctor’s office, I looked at a ballon sticker on the wall. That made me think (once again). Would it be possible to make...
Thread by: doglover9754, Jan 10, 2018, 18 replies, in forum: General Physics

### B What in gravity makes water on Earth into a ball?

So, from my last thread “Why doesn’t the water fall out of the Earth?” I asked if the reason why water doesn’t fall out of the earth even on its...
Thread by: doglover9754, Jan 8, 2018, 25 replies, in forum: General Physics

### B Is it possible to make gravity stop?

I know this is probably going to sound stupid but I'm really curious for the opinion of someone who has knowledge. Well spacetime is like a...
Thread by: Odette, Dec 24, 2017, 5 replies, in forum: Special and General Relativity

### B Origin and demonstration of Newton's second law

At highschool, we saw without demonstration the fundamental principle of dynamics (2th Newton's law), i.e : \sum \vec{F}=m...
Thread by: fab13, Dec 22, 2017, 1 replies, in forum: General Physics

### I Experimentally measure gravitational force

Can we experimentally measure the very weak gravitational force between two objects just like we can detect magnetic field lines by a deflecting...
Thread by: Taseng Mancheykhun, Dec 13, 2017, 3 replies, in forum: General Physics

### B What would happen if you take a piece of a pulsar

Hi, what would happen if you took 1 cubic meter of matter from pulsar into empty space what would happen does the matter will expand since there...
Thread by: johnpro1, Dec 3, 2017, 1 replies, in forum: General Physics