# Tag Info

## Hot answers tagged physics

20

No. The way we define latitude and longitude is based on the planet's axis of rotation. You can certainly (AFAIK) have a planet with a 90° axial inclination, or (probably) a planet that is identical to Earth except with all the land masses rotated 90°, but unless you completely change the definition of "pole", the poles will, by definition, be stationary w.r....

15

Neutrinos have, believe it or not, been proposed as a method of spacecraft propulsion - see Morgan (1999). The idea is a bit different from yours (which I believe has not been explored yet), inasmuch as it relies on the production of neutrinos, rather than using existing ambient neutrinos. This idea utilizes the decay of muons, heavier cousins of electrons. ...

14

Your astronaut would be protected in the same way as the ship. It is bad to be hit by a very fast piece of stuff. Very bad if you are alive, but also bad if you are not alive and you get hit over and over all the time. The latter is the case for your ship. Pieces of space dust and particles are plowing into it and ablating it. And going right thru it. ...

11

Talking about any speed is meaningless unless a reference frame is used. Since you cannot sense your own speed, you must use objects as reference points. For the sake of the question, lets assume that your heroes started on a planet, which is located in galaxy not much different than our own. To accelerate to 0.3c relative to the star you started on would ...

10

I'm going to assume that the question you're asking is 'Can the Earth additionally rotate up-and-down?', because, Matthew's answer has pointed out, we define 'up and down' based on the planet's already spinning axis. The only way this question makes sense is that you're asking whether the Earth can additionally spin up-and-down. And the answer to that is a ...

8

The issue with harnessing the neutrino-electron interaction is the cross-sections involved. Since neutrinos are charge-less, and interact only via the weak force (gravity also but that won't help us here), they are more likely to interact with larger particles. For this reason, neutrinos-nuclei interactions are the most common. While neutrinos can (and do ...

6

I think you're confusing a superfluid with a supercritical fluid given that your temperature and pressure is basically at the critical point for supercritical co2. These are significantly different states of matter. Liquid matter will typically go through a phase change when heated or decompressed (boiling). Conversely it will go through a phase change when ...

6

If you are just relying on friction to hold the human against gravity (meaning nothing piercing in the human body to grapple it), you need to equate the weight of the human to the static friction between the creature's pincers surface and the human surface. $m_{human} \cdot g = F_{pincers} \cdot \mu_{static}$ From the above $F_{pincers} ={m_{human} \cdot ... 5 You'll be scooping up interstellar medium at significant kinetic energies. There's two problems: The atoms that hit you will actually accelerate you away from your position (pressure measured in Pa), and of course they'll impose a radiation hazard as you absorb them (radiation dose measured in Gy). Let's do some math. Let's assume an interstellar medium ... 5 You might be interested in reading up on the Bereakthrough Starshoot program. The concept is to send a thousand nano light sail spacecraft each with a camera, to Alpha Centauri, at 0.2c taking approximately 50 years, propelled by a laser beam from earth. One way only, of course. They would be protected by a thin, light ablative coating to protect them from ... 5 Unfortunately, no. Referencing the comments made by both @AlexP and @DWKraus and noting that one of the articles you cite states, "The detailed mechanism of the cicada's song is far from fully understood...." In other words, my answer is a best-guess. A human-sized cicada would produce sound with a substantially lower frequency. Your largest cicada species ... 5 Gravitational waves Presumably, there would be gravitational waves emitted as the two compact objects slowly came close to merging. Given their small cross-sections, a direct, head-on collision is highly unlikely. A more plausible scenario involves an interaction with a third massive body.$^{\dagger}$The white dwarf and neutron star would be inserted into ... 4 In school physics classes, a spring is just a spring, and you learn by hanging weights and measuring deflection how to find the constant spring modulus$k\$, up to the point where you exceed the elastic limit and your spring deforms into a messy wire. The real world, as with most things, is nowhere near that simple, and engineers can create a bewildering ...

4

The planet will instantaneously explode. The earth has a gravitational binding potential of about 2.25×10^32 joules, or the weekly energy output of the sun. This energy also currently being counterbalanced by potential energy of the compression of rock in the earth which prevents the earth collapsing to a point. Without gravity, it will all be released at ...

4

As you say, Uranus does. All it would mean is that the axial tilt would be 90 degrees. This is unlikely in the course of normal planetary formation, so (as with Uranus) it would probably take a series of impacts early in the planet's history to point its axis in the appropriate location. Now, if we're talking about Earth, things would obviously look a lot ...

4

The inhabitants of the ship would know where they are going and know the day and year length of the planet they are going to because of advanced astronomical observations before the ship left Earth. The most logical approach would be to immediately adopt a clock and calendar compatible with their new home and measure everything against that. The trajectory ...

4

If the person is willing to be picked up, the pincers only needs to slide under the armpits and lift the person like a fork lift. This means the only presure the person should experience would be from thier own body pressing down on the pincer from gravity. If the person is unwilling there is no exact equation for this since humans will vary so much in ...

4

Yes, in combination with other skills Your residents are going to use a combination of techniques to navigate. Echolocation is a way of avoiding obstacles, not of navigating over longer distances. In the Wikipedia image below, the bat can tell that there's a box ahead on its left, but the bat has no idea what's on the other side of that box. If your ...

4

If you manage to interact with neutrinos to any practical extent, a lot of possibilities open at once: Energy from the star neutrinos - the Sun emmits some 15% of its energy in neutrinos, you can harvest them even in some planet's shadow. Hotter-core stars are even better in this regard. Neutrino sails - to harvest neutrino momentum. If you can interact ...

3

Having 0.3c related to any known macro object in our university pretty much imposes having ~0.3c related to anything else (redshifted objects included, if/when you reach near them). At 0.3c all those stray helium and hydrogen atoms will behave as both deeply penetrating and ionizing radiation. At 0.3c you will "collect" a lot of them, even in the space ...

3

The water phase diagram can help you understand how the interface will behave. The transition from liquid to solid is sharp, by changing the pression like you would have because you are going lower or higher, you would go from the liquid to the solid phase (you would move along a vertical line in the chart). Local temperature variation (horizontal in the ...

3

The idea of springs or pogo sticks, already proposed by Willk and Darrel Hoffman is interesting. Let's do the maths. The main problem is the sudden deceleration: it's not the fall that kills you, it's the landing. We can limit this deceleration using two methods. Minimizing the terminal velocity: the skydiver should be in a belly-to-earth, face down ...

3

The rubber on climbing shoes is surprisingly sticky. So long as you're exerting SOME force into the wall, they will probably stick. With that in mind... What I'm imagining is sticky rubber pads on the hands and feet of your exoskeleton. When you want to descend, you jump at the wall of the building opposite where you are standing. When you reach that ...

3

Anecdotally: probably. Compare the Horseshoe Canyon Ranch, which is in the Ozarks. The Louisiana Center for the Blind takes blind trainees there annually, with lots of room for said trainees to wander off unsupervised between (and sometimes during) scheduled activities. More relevant to the question (it isn't precisely a city carved into a rocky canyon, ...

3

There are some exceptional real worlds cases of humans using echolocation, take a look at https://en.wikipedia.org/wiki/Human_echolocation to see a few. There are videos where people avoid obstacles, sink basket balls and take hikes along rocky paths. In a demonstration in a documentary I can't recall the name of Ben Underwood could even successfully detect ...

3

Yes, Absolutely! Not only can you do such a thing, but in fact boatloads of alternate metric theories of gravity have been proposed both before and after Einstein came out with GR. For instance, the first metric theory of gravity was actually due to Nordström in 1913. Let's go over what exactly the equations governing GR look like, and then we can dig into ...

2

It is possible with a piece of equipment. Excuse my ASCII art: _______ \o| n n | I| | | n n | | | Our guy would have a hard wing made out of some material that can be folded and expanded. In order to scale down the building, he will just jump close to the surface. This requires your sandpaper like system for friction too. Now the ...

2

As many other answers have pointed out, the problem with friction is that you need a normal force pushing into the wall. If your suit has one or more wings (or an array of tiny airfoils) that deploy during the fall in the direction of descent it will create a normal force into the wall - like aerodynamic lift but horizontal. If the coefficient of friction ...

2

Leg springs You could do something like the long fall boots used by the protagonist in the Portal games: These look a little too simple for the job, of course. The way they attach to the legs seems highly insufficient. But you could modify this concept by attaching them to the back of some sturdy boots. (I don't recommend using them barefoot as in the ...

2

On Earth, the deepest point in the ocean is Challenger Deep (36,200 feet) and the tallest mountain is Mount Everest (29,029 feet). Mount Everest is roughly 65,000 feet taller than Challenger Deep, so if you parked the two next to each other and raised the ocean levels to just below Everest's peak (RIP life) you could have an ocean more than 12 miles deep. ...

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