# Karthikeyan KC

## Forum Replies Created

Viewing 15 replies - 1 through 15 (of 112 total)
• You’re right. Fundamentally for nuclear fusion to occur on Earth, you need very high temperatures and pressure so that the hydrogen isotopes (basically two protons) overcome their mutual repulsion to fuse together.

At the core of the Sun, the pressure is extreme (26.5 x 10^15 pascal) due to the gravitational force of the hydrogen and helium. And this pressure contributes more to creating a viable condition for the fusion.

On Earth, however, you cannot create such high pressure. The highest pressure we could possibly achieve in our fusion reactors is around 2.5 x 105.

The denser and hotter the plasma is the more chances of fusion to occur. Hence, on earth, we make the plasma hotter than the core of the sun and try to achieve high densities (which means we are trying to achieve higher pressures too).

I hope this helps, Shamil. Thanks for visiting Geekswipe. :)

• It depends. It should burn as long as the oxidizer and fuel are in contact and enough heat is provided to ignite it. The primary challenge might be the heat you’ll need for ignition. For effects of temperature and pressure, you’ll need to consider the phase changes of the oxidizer and fuel compounds used, how it affects their thermal properties as well. For depths like Mariana Trench (108 Mpa and 1 °C), I think an underwater flare would probably work if you provide enough heat to ignite it in the first place.

• The likely explanation is that you might have seen a meteor. The green glow could be attributed to the chemical composition of the meteor itself.

• Hi Ben,

It’s not. Your existence is the result of energy transfer and not energy creation. Biologically you evolved from a zygote — a cell, which is an open thermodynamic system with its own state variables like volume, pressure, temperature, etc. That zygote did not come into existence by magic. It’s from the fertilization of the sperm cell and the egg cell. Energy is just transferred from the surrounding to the system and vice versa, changing the state variables. It is conserved during the process.

As the mother consumes food, they breakdown and gets converted into energy (metabolism) which helps in cell division that forms the embryo, which develops into a fetus, and then into the baby you.

Hope it’s clear now.

• Hi! Welcome to Geekswipe. For your question, of course, the answer is yes. Aluminium has a high thermal conductivity than steel. So the aluminium radiator certainly helps. And with the added benefit of another radiator with a much larger surface area, you can expect a faster convective heat transfer. Larger the surface area and higher the conductivity of the heat exchanger, the faster the heat transfer is.

If you wouldn’t mind, can you post the picture of your setup? Just curious!

• It may be, however, that the earth’s wobbles month by month and year by year are too slight to be measured.

@m1-6eek-5w1pe, you are right. The perturbations are too small if measured within a certain period of time. So for the long run, it is an iterative process where we will revise the celestial coordinate systems including all the perturbations at certain reference points in time. You might know these points as epochs.

I rather assumed that these changes are measured and recorded.

Yes, they are. And you can compute them for future dates as well. You can find them in an astronomical ephemeris. You can find one at NASA’s Solar System Dynamics website. But this one shows the data you need with J2000.0 as the reference epoch. For your case, you will need a similar calculator but one that uses up-to-date equinox data. Perhaps NASA’s SPICE is what you are looking for. Found a geometry calculator based on the SPICE data as well.

• Hello Geoffrey. Yes, all the planets in the solar system revolve around the sun close to a disk-like plane with a little inclination and eccentricity. For Earth, the orbital inclination is about 7 degrees related to the Sun’s equator. The eccentricity of the orbit is 0.0167. And you’re right, the orbit does change over time and this can be recorded.

And as we observe and record everything from the Earth, we keep our Earth’s plane as the reference plane and call it the ecliptic. We observe other celestial objects relative to this ecliptic. So, for the orbital motion of the Earth relative to Sun, we can simply track the Sun’s position throughout the year. The coordinate system is called the ecliptic coordinate system. It can either be geocentric like the above case or heliocentric.

And as mentioned, there will be significant changes in the orbit over a longer time—but like in thousands of years. As it involves other planets in the solar system, it’s an n-body problem. The orbital change will be due to perturbation effects. From planets like Venus and Jupiter heavily affecting the eccentricity of the Earth. The precession of the Earth. The axial tilt. And other complex orbital perturbations along with any unexpected celestial activity that affects the solar system. We call the cyclical effect on Earth as the Milankovitch cycles. Hope this is what you are looking for.

• Hi! This is very interesting. Maybe it’s not photoelectric effect at all. Could it be because of the thermal effects? Try playing with the intensity of the laser perhaps. Also, how are you generating the frequency? And maybe the other factor could the phone itself. The laser could be aimed at the hole where you assume the mic is, but on some smartphones, the mic is placed at an angle to avoid accidental damage—like when someone uses the mic hole to eject the SIM tray instead.

Image credit – Dominik Schnabelrauch under CC BY-NC-SA.

• The waves are nothing but a physical vibration of air molecules. So when an object moves through the air, it interacts with the air molecules like how a boat or a submarine interacts with water.

In your case of a moving object, these air molecules get compressed in the direction in which the object moves. This is because the object has a velocity and this keeps pushing the air molecules as it moves. And like you said, the frequency of the waves will be higher at the front of the object. But at the opposite, the frequency of the waves will be lower as they are not packed up together (imagine the same boat and wave analogy). Yep! This is the doppler effect.

And in your second case of a stationary omnidirectional sound source and a stationary observer, the frequency of the sound will be constant in all the directions. Why? Because the object is stationary and it’s not compressing the sound waves in any direction. The sound waves have their original frequency. The volume at the observer’s end will be less audible as the amplitude of the sound wave is inversely proportional to the square of the distance – aka inverse square law.

And here is an interesting case! When the object starts travelling closer to the physical maximum limit of the molecules could travel (speed of sound), they keep stacking up together like a barrier. And when the object travels faster than this limit, it breaks that barrier and causes a sonic boom. Read more on how sonic boom works.

• I play FPS, Battlefield mostly, from 8 PM to 10 PM. I have found that I play better right before dinner time. During that period, on CTF and rush rounds, I find myself aggressively focused, serious on the lead, and my reflexes are pretty good. After dinner, I just feel relaxed and unfocused. If I choose to play after a meal, I’d rather idle on a defensive line with support or recon class.

So it might be a placebo that makes my brain work more and focused on a reward – dinner. Also, as mentioned by @san, it could be the hunger hormones activating my brain to be more focused. So your guess is right. Mild hunger is likely to improve a gamer’s performance. But I cannot say the same for coding though. It’s the other way for it. Compared to coding, gaming doesn’t demand huge brainpower.

• I understand where you are coming from.

Density is the mass of a substance per unit volume.

$$\rho = \frac{m}{V}$$

And you are right about the volume. The volume of water increases when it freezes due to its molecular structure. But as the mass is constant the ice becomes less dense when compared to liquid water. This is why ice floats on water.

But the sea levels do not rise when sea ice melts. Because they are formed in the sea and it’s just a phase change and no additional mass is added, hence no displacement.

It is the glacial ice and ice sheets that rise the sea levels when they melt—as they are not in the ocean in the first place. The glaciers and ice sheets are part of the continental land and when they melt and flow into the ocean, they add extra water—freshwater—into the ocean. This increases sea levels around the world.

In addition to this, as the Earth gets warmer, water itself expands thermally and contributes to the rise of ocean levels.

• The ‘feel’ of gravity on a spaceship’s centrifuge (like that station you’d see in 2001: A Space Odyssey or Hermes from The Martian) is because of the centripetal force exerted by the centrifuge. Any occupants inside the centrifuge would then experience the centrifugal force, which they perceive as ‘gravity-like force’.

The reason why you see centrifuge concepts that has the longitudinal axis of the spaceship as its axis is could be attributed to convenience and convention.

In space, there’s no sense of any direction. Whichever way gravity pulls us, we call it ‘down’ and the opposite side as ‘up’.

For a spaceship, there are three primary axes and hence three possible configurations. For the following cases assume that the centrifuge is in operation as the spaceship accelerates.

1. Centrifuge mounted in the usual way with its axis being the longitudinal axis of the spaceship.
2. Centrifuge rotating around the lateral axis of the spaceship.
3. Centrifuge around the ship, i.e, with the vertical/normal axis of the ship as its axis (your question’s case).

## Case 1 – Longitudinal axis

In this case, we have a centrifuge like the Hermes. In the figure below, the axis of the centrifuge, the longitudinal axis of the ship, is passing out of the screen towards you.

Longitudinal axis.

Here, we’d experience the ‘artificial gravity’ radially outward from the ship, as the walls of the centrifuge exert a centripetal force on the occupants.

And in this case, our ‘down’ is always facing away from the ship at all points. When you look ‘up’ you will always see the centre of the spaceship.

And if the whole ship needs accelerate temporarily by firing its thrusters, the occupants of the centrifuge, at any point, would feel an inertial force acting to their side and it won’t be affecting their ‘down’.

## Case 2 – Lateral axis

In this case, consider the centrifuge to be mounted on either side of the spaceship as it rotates with the ship’s lateral axis as its axis. Think of it as a spaceship with two centrifuges (like wheels) on either side.

Lateral axis.

When the spaceship accelerates, at points F and H, you’d feel the inertial force pushing your feet and head. At F, you’d feel lighter and at H, you’d feel heavier. And as the centrifuge rotates, the direction of the inertial force changes and it would be uncomfortable than the previous configuration.

In other words, as the spaceship accelerates, your ‘down’ and ‘up’ are affected as the ∆v causes an inertial force that adds varies your inertial force perceived at F and H.

## Case 3 – Normal axis

Like you’ve mentioned in the question, If the centrifuge runs around the spacecraft—with the normal axis of the ship as its axis, the experience would be similar to that of case 2, except in a different plane.

Normal axis.

I guess this is one of the reasons why case 1 (longitudinal axis) is the preferred choice of configuration. But in any case, if the ship decides to fire the thrusters and accelerate, the centrifuge will be stopped, locked, and the crew will be asked to strap into their stations. In that scenario, the configuration doesn’t matter, as the only acceleration will be from the ship’s propulsion and you can orient yourself to it—which is also a type of ‘artificial gravity’.

I’d call case 1 as the safe choice for engineering reasons too. Configuring the centrifuge along the longitudinal axis doesn’t subject its walls to varied stress, unlike the other two configurations. In this type, the stress from the inertial forces are uniformly distributed, even when the centrifuge is in operation. Hence configuring it along the longitudinal axis eliminates or minimises structural failures during planned and unplanned acceleration events.

Case 1 is the winner! :)

• Thanks! :) Excited and hyped!

• I am glad I could help.

• And…there’s no such thing as a “sound wave”? It’s **just** air, just the atmosphere we know, but vibrating?

Spot on! Yep. Sound is just the air molecules vibrating at different frequencies. It’s a pressure wave. No, nothing new is released into the air, because it’s the air that is vibrating in the first place. If there’s no air, there won’t be any medium for this vibration (sound) to happen. This is why you can’t hear sound in space.

Also, in the case of light, it is the oscillations of electric and magnetic fields — one of the fundamental properties of the universe and it does not need a medium to propagate. Whereas, the sound is a compression wave, oscillation of air particles. It is just a property of the medium (air). In other words, for sound waves to exist, you need a medium like air or water. Electromagnetic waves exist because the universe fundamentally has it.

Viewing 15 replies - 1 through 15 (of 112 total)