3,466 reputation
1713
bio website none
location San Mateo, CA
age 59
visits member for 3 years, 4 months
seen 5 hours ago

Aug
16
comment Does decreasing the length of the line between a harness and zip wire increase the velocity at which you travel?
If I had to guess, the long harnesses for customers go with trolleys that have more resistance in the wheels. It is not about the length of the line, but about making sure the customers don't arrive at the bottom with too much speed. The instructors have training and gloves so they can slow down when needed.
Aug
15
comment Heat transfer to a cube from one of the faces
With a heat flux of $10$ MW in a few cm everything will vaporize quickly.
Aug
15
comment efficiency of electric cars vs gas?
Your points are good. One counterpoint is that it is easier to control emissions from a few powerplants than from a million cars. These tradeoffs are hard. In your case, it depends on what the source of electricity is. In any case, you are not crazy.
Aug
10
comment Is it possible to 3D print a mirror to create a high quality telescope?
If you can print a thermally stable material, the stairsteps may be unacceptable, but you can be very close to the desired contour. It would be a very good start for some polishing.
Aug
8
comment Why does this model fall apart when angular velocity is small?
If you show your derivation, it would be easier to comment. It can't be friction-there isn't any. You may have a small angle approximation you are using. It seems like $r$ should go smoothly to $0$ with $\omega$
Aug
6
comment Which is the most accurate way to model the fundamental atmospheric parameters of the Earth?
What data do you have? All these things change with time: the weather changes. If you want accuracy, you need current observations.
Aug
5
comment Where does the number “380,000 years for electrons to be trapped in orbits around nuclei” come from?
@ratchetfreak: A "short while" after the big bang time is well defined. Unless you think the "short while" is significant compared to 380,000 years, it can be ignored for this purpose.
Aug
3
comment Normal modes of the 2D double pendulum
If it is a normal mode the amplitude of every point should decrease steadily and smoothly. If it is not a normal mode, some amplitudes will increase as energy flows around. Think about the coupled pendulum. If you measure the location of one pendulum and start by exciting just one, the observed amplitude goes from 0 to max to 0 to max ... If you excite a normal mode, the amplitude of a pendulum just decreases smoothly due to friction
Aug
2
comment Does it take a lot of energy to heat metals up?
Metals tend to be good heat conductors. When you touch one, the heat from your fingers is conducted away, which is why they feel cold. When you touch an insulator, like a coffee cup, you quickly warm up the small volume around your fingers, so it doesn't feel cold. That may be what you are thinking.
Aug
2
comment Conservation of energy in transformers
@Rohit: No, this becomes a voltage to be considered. So if you plug a $10:1$ stepdown transformer into a $120VAC$ outlet, you have $12VAC$ at the output. If you connect that across a $2\Omega$ resistor, you will draw $6 AAC$. That will draw $0.6 AAC$ from the wall. The back emf is then $120VAC$ and all is well.
Jul
29
comment Intuitive explaination for why higher engine compression ratio is more efficient?
@Kyle: No, compression is a good thing even if combustion is complete in both cases. As Floris says, the heating makes much higher pressure after compression, which energy can be extracted.
Jul
26
comment Is it feasible to detect light emitted from planet earth 2,000 years ago by reflection from an object situated 1000 light years away?
There is a huge difference between detecting total illumination and resolving images. Astronomers are detecting light echos of events, but there is a lot of integration (averaging) going on. You can get a (time convoluted) light curve, but resolving detail seems out of bounds.
Jul
25
comment Could two identical stars revolve around each other in a common orbit if we only account for Newtonian physics?
How close do they have to be for you to consider them identical? I believe similar mass binaries have been observed, but don't have a catalog at hand. The Hulse-Taylor pulsar is two neutron stars-that is pretty similar
Jul
24
comment Could two identical stars revolve around each other in a common orbit if we only account for Newtonian physics?
You are being ill-served by the remark that the earth revolves around the sun. That implies that there has to be something there to revolve around. In fact, all bodies of the solar system revolve around the common center of mass. Since the sun is so massive, it approximates the center of mass, which is where the remark comes from. Jupiter is about $1/1000$ the mass of the sun, so the sun-Jupiter CM is $1/2$ million miles from the center of the sun, which is slightly outside the sun. Does that meet your "observed?
Jul
24
comment Calculate the current in mA which will be flowing through the two resistors
You only list three resistors. There is no mention of a resistor in series. You are asked to calculate the current in the "other two resistors", the $3 \Omega$ and $5 \Omega$ ones.
Jul
24
comment can we get electrical energy from gravitational energy?
Note that a retrograde orbit does not have any higher orbital speed than a standard orbit. It will have a higher speed relative to the surface or the ambient magnetic field, but not a whole lot for a low orbit satellite. It is probably not worth the extra work of getting to a retrograde orbit.
Jul
24
comment How do heated showers/faucets work?
Yes, there is a water heater with a tank that keeps the water heated. Typical US home ones are 30-50 gallons (120-200 litres). Typical temperatures are 120-140F (49-60C). When you turn on the hot water, it takes a while to get hot because the water stored in the pipe between the heater and the shower has cooled.
Jul
22
comment How to measure rainfall? And how is it determined for a specific location?
50 miles is an enormous distance. Near San Jose, CA, we have places within 20 miles that average 10 and 80 inches per year. Think Kauai, HI, which has Mount Waialeale, the "wettest place on earth" averaging 462 inches per year, while Poipu averages 30-40 inches per year. To my eye they are about 15 miles apart.
Jul
19
comment Possible intergalactic celestial objects
My point is that I think all of these can be ejected from galaxies, but some will be hard to see at long distance. For weakly bound ones, you need to make sure that the tidal forces do not disrupt the system. When you do that, you may lose the outer reaches, but you may eject enough to count as whatever category you are interested in. Certainly we can't see asteroids outside the galaxy.
Jul
18
comment How to measure rainfall? And how is it determined for a specific location?
It varies a lot. In general, a heavy storm will be heavy over a wide region. In some places rain is quite localized-you should see what happens where you are interested. Even once you get a rain gauge there are issues-trees, overhanging roofs, etc. I have no clear spot in my yard to set one up. You also have to worry about the effects of rain not falling vertically-it often doesn't.