# Questions tagged [physics]

How physics applies to a particular activity in space or to getting to space.

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### Gravity assist and the terrestrial analogy: why does the velocity double?

The Wikipedia article on Gravity assist has this terrestrial analogy: Imagine standing on a train platform, and throwing a tennis ball at 30 km/h toward a train approaching at 50 km/h. The driver ...
463 views

### Can I use an ice cube as a re-entry heat shield?

A comment on recent popular question brought me to Stirring Tea and this entry To boil a cup of water, you'd have to drop it from higher than the top of the atmosphere. If that is true, in theory ...
2k views

### How can solar wind be supersonic?

I was reading this Wikipedia article on Heliosphere and was confused a bit: this supersonic wind must slow down to meet the gases in the interstellar medium How can sonic speeds exist in space? ...
3k views

### How does centripetal force produce artificial gravity

I think I lack a fundamental knowledge of physics to answer this myself. In many sci-fi stories, there is a rotating spaceship that gives the feeling of being pulled "downwards" against the sides of a ...
499 views

### Linear motion reaction wheels?

So, as I've recently learned, reaction wheels rotate a craft with Newton's Third Law, remain spinning while the craft should rotate, then stop, resulting in no rotational speed, but after having ...
830 views

### What's the nature of hoop stresses on a rocket nozzle?

On a rocket nozzle, are the stresses (namely hoop stresses) from pressure differentials compressive or tensile? Obviously, in a combustion chamber, the pressure inside is greater than outside. As ...
1k views

### Could a ship be launched from a mothership while in interstellar space? [closed]

Say you've got a mothership that is on its way to a star. Could you launch a smaller ship from it while it's in either the coasting or braking phase of the journey? A scout ship, for instance. Or ...
106 views

### Kinematics help

If a constant acceleration starship started at rest, then accelerated at 25G (245m/s^2) how long would it take to fly an AU (149 597 871 kilometers)? I am a writer, so I have no experience with ...
357 views

### How can a spacecraft gain more energy from burning the same amount of fuel, but at different times?

Here it is very simply: A hypothetical spacecraft has total mass of 1000 kg and a main engine that has an effective exhaust velocity of 3 km/s (or 305.915 seconds if you want Specific Impulse in ...
3k views

### Does the Sun actually move on its own, or does it move with the Solar system? [closed]

I'm curious, does the Sun actually move? The concept behind the question is, if you wear a shirt and you move, does the shirt actually move? Like the Solar system orbits around the Milky Way, but does ...
6k views

### If I drop a feather from orbit, would it burn up or "hit" the ground?

I know that capsules typically require heat shields to survive reentry from orbit. I'm wondering how an object's size, density and aerodynamic profile affects this. For more specificity: The feather ...
5k views

### Why do some meteors explode in air?

I was reading about the Tunguska and Chelyabinsk meteors and I wonder what would cause a meteor to explode in the air, instead of hitting the surface?
5k views

### Why can't we launch from space?

So this may be a stupid question but I was wondering why we couldn't launch from space. I know that most of the fuel that we spend is for escaping Earth gravity. Yet, if we have already done this with ...
200 views

### What is a "warp bubble"? [closed]

There has been rampant speculation relating to the EMdrive lately. One such speculation talks about "warp bubbles". I'm not familiar with this concept. Is there a scientific definition of what ...
6k views

### Why aren't the ISS's nor Space Shuttle's radiators black?

As we know, from a surprising corollary to Kirchhoff's law of thermal radiation, just as darker* objects absorb more light (and therefore energy), darker objects also radiate more light (at lower ...
11k views

### What does the exhaust plume of a rocket look like in vacuum?

There are plenty of photos of rocket tests and launches in atmosphere, and in these the exhaust plume tends to be a long thin flame. Is this true for when rocket engines operate in a vacuum? My guess ...
6k views

### Accelerometer in space

If my understanding of the General Theory of Relativity is correct, according to the Equivalence Principle, forces due to gravity and acceleration are indistinguishable. If that's the case, then an ...
187 views

### Do modern CFD codes reduce the number of test firings in an engine program?

Given the complexity of liquid propellant rocket engine development, I wonder if (and how much) modern Computational Fluid Dynamics (CFD) codes help to reduce overall development costs. Do they ...
20k views

### Why don't the Space Shuttle's tires explode in the vacuum of space?

According to this NASA article the tires are inflated to 340 psi (main gear) and 300 psi (nose gear). At landing, there is significant strain, but what about in space? Are the tires exposed to vacuum ...
1k views

### Speed limit while "Orbiting" a fixed point in deep space

My co-workers and I had a debate if there is an "orbital speed limit" for a given altitude over a celestial body. According to Kepler's laws it appears you cannot. My co-worker proposed the following ...
8k views

### How do jetpacks work in space?

I've seen in some videos of astronauts that they used to use a jetpack type system to maneuver in the vacuum of space around the ISS and other satellites using pressurized gas. From Wikipedia ...
2k views

### Why does the Earth lose rotational velocity in the vacuum of space?

I think it is a well-known fact here that the Earth is slowly losing rotational velocity over time (some 1.4 milliseconds of the day are gained per hundred years). Eventually, this means that the ...
14k views

### Why don't we use catapults to get to space?

Stupid question obviously. But did you ever had an idea which sounded so brilliant, but you know it is totally stupid? So, lets hear my idea: Do you know how we launch jet fighters from navy ships? ...
2k views

### Does the Falcon 9 v1.1 form a shock diamond when in flight?

How does the Falcon 9 v1.1 form this exhaust pattern with its nine Merlin 1D engines? Is it a bigger, rougher shock diamond? I am trying to learn more about how one could form with a cluster of ...
43k views

### What will be the effect if we stand on Jupiter?

As we all know Jupiter is a gaseous gas giant and it has a large mass, almost twice the sum of all other planets in the Solar system. So, if it happens that we go to Jupiter, and, as we know it does ...
1k views

### What would it look like to shatter a glass or break similar material in Zero Gravity?

I just had this thought today: I wonder what the shattering would look like if you "dropped" a glass or a ceramic cup in zero gravity. Obviously you can't drop it, you'd have to like throw it. But ...
7k views

### What would happen if I throw a grenade in space?

What would happen if I throw a grenade in space? Would it explode? Or will it just keep floating forever?
137 views

### How do magnetorquers work? [duplicate]

I'm working on a project that involves magnetorquers, and as someone with only a basic understanding of physics (and even more basic understanding of electromagnetism), I have absolutely no idea how ...
3k views

### Oberth effect for Earth vehicles

I don't understand this and must ask a probably very stoopid question here: The Oberth effect says that a rocket is much more efficient when (and in the orbital direction of) a payload when it ...
2k views

### What is the barometric formula for a gas giant?

The barometric formula describes the atmospheric pressure depending on height and a host of other things. This formula assumes a constant gravitational acceleration over the whole height of the gas ...
1k views

### Can you have a rainbow on any bodies in the solar system besides Earth?

We know from Flying on dense atmosphere planets & moons that many bodies in our solar system have sufficient atmosphere for at least the concept of flying to be considered. What about the ...
1k views

### Physics and math behind flight through solar system [closed]

I wrote a program that simulates a solar system. I was able to calculate the locations for every planet on its elliptical route for any given time. In a second project, I managed to simulate newtonian ...