# Search results

1. ### Why gyroboards are said to run so long on one battery charge...

Hello Ads say a gyroboard with the battery 48V 4.4AH, and the motor 700 Wt will run for 2 hours at the speed of 20km/h ! But - simple physics - will not the motor drawing about 10-15 Amp exhaust the battery in just some 20 minutes !? Do ads lie ?
2. ### Mercury in air

2 statements from an article : "WHO standards for occupational exposure to inorganic mercury are currently 50 µg/m3 in air ...... WHO's maximum acceptable daily intake (ADI) for mercury is 40 µg/day." An average person inhaling 20 m3 of the air containing 50 µg/m3 of mercury, inhales...
3. ### Water density / volume

Water density at 0 C is 990 kg/m3. Water density at 100 C is 1030 kg/m3 - 1 m3 of water "loses" about 4 % of its mass. Water expansion rate is 1.0002 for each 1 C increase in temperature - 2 % for the above rise from 0 C to 100 C.. How comes that water density decreases 4 % but its volume...
4. ### Measurement points for fan performance curve

For finding fan performance curve where better to put static pressure probes - near the surface or near the center of the duct ?
5. ### Water as coil core

water as coil "core" How much a coil inductance of 0.1 mH (3 cm long, some 50 turns wound around 5 cm diameter empty plastic pipe) may change when water enters the pipe ?
6. ### The capillary action's limit

Is it feasable to achieve elavation of water to, let's say, 10 m height due to the capillary action effect ? Or the capillary diameter for that to achieve should be less than the water molecules themselves ?
7. ### Oil boiling point at vacuum

What may be the boiling point (temperature) of a refrigeration POE oil at, let's say, 500 microns absolute pressure ?
8. ### Directing dangerous objects to Sun

I have never heard about a plan of cosmic objects endangering Earth to be directed towards the Sun in order to get rid of them. It is unfeasable ? "Sun wind" blowing from the star is stronger than its gravitation ?
9. ### Partial pressure

Am I assuming right the pressure in a vessel holding two substances (both being in the both liquid and gas states) will be equal to the saturation prerssure of the one which has the higher SP ? That is, for substance A whose SP at a given temp. is 10 B, for instance, and substance B whose SP is...
10. ### Ac lagging

AC, as is known, "lags" voltage in a coil and we are familiar with the drawings of the two sine waves with the 90 degree angular "shift" between them. For 50 Hz the shift translates into 5 µs "lagging" but, for instance, for 0.05 Hz AC it would indeed be 5 s ? What I mean : frequency does not...
11. ### Speed of Earth on its orbit

While the mean speed of the Earth on its solar orbit is about 30km/sec, what is its approximate speed during the both equinoxes and the both solstices ?
12. ### The Earth as pendulum tied not to the Sun

The thought came to my mind yesturday : does not Earth in its movement looks like pendulum tied to the Polaris ? Only the very long one - comparable to an object swinging about 1 cm circle at a tie of about 15 000 km (if my quick calculations now are correct).
13. ### Question on work and energy

Ignorant as it sounds, what 1kW of energy spent on having moved an object from point A to point B would be really spent on ? Is it, 1. acceleration /desceleration of all moving parts of both the engine and the object itself, and 2. overcoming by all moving parts (including electrons in wires) of...
14. ### Friction heat generator

Friction is phenomenon we try to avoid but it may be useful. Does anyone know about existing friction heat generators and what method they use ? Seemingly, solid matter does not suit as it pulverizes as well as wears out the generator parts. Probably, remains gas compression. There cannot be a...
15. ### Static pressure inside an air conditioner's capillar

Let's a system be as follows (with approximate but, still, real numbers). Compressed refrigerant gas get condensed in a condenser and as liquid with +/- 15 B SP enters a capillary (a "metering device"). It exits the capillary at high speed and enters the pipe leading to the evaporator having...
16. ### Water speed in the closed system

Does water speed in the pipes having the same diameter is strictly the same in any point of a closed (heating) system (with pump working) ? On the contrary, although liquids are "incompressible" in practice, however, does the piping still allows it to be so : the more far the water from the...
17. ### Hydraulic resistance's unit ?

For better understanding of it's principles, electrotechnics is often compared to hydronics (and, probably, vice versa). But, why having the electrical resistance to a flow of charged particles - with it's basic unit "Ohm", there in general Physics is no unit of measurement of the hydronic...
18. ### Hydraulic total pressure

Total pressure is a sum of the static pressure and the dynamic one, and is said to be the same along a pipe/duct. In the water pipe gauge (static) pressure is maximal after the pump and minimal at the pipe outlet, but the speed and the density being the same, the dynamic pressure is the same...
19. ### Degree of vacuum of Universe

Hello It seems we refer to the outer space as "the absolute vacuum." I read recently that the deepest vacuum man reached on the Earth is about 1000 molecules per cm3. To obtain this there was needed energy sufficient to reach a pressure of 400 billions Bars. Why space ships do not burst like...
20. ### Gas density at vacuum

What is the formula to calculate gas (air) density at negative pressures, as well as water content ? For instance, a vessel with air with volume of 1 m3, density 1 kg/m3, and water content 10g /m3 get vacuumed from 1BarA to 0.1BarA isothermally.
21. ### Universe's full cycle: explosion - implosion

While Universe now continue to expand due to the last BB, there is growing vacuum in the midst of it which with time will reach such tremendous value that the expansion will be stopped and the reverse process will start ?
22. ### Air Δ P on a resistance

Where in an air supply duct (after the fan) an air damper (or any other resistance to flow) will have less Δ P : closer to the fan, or closer to the outlet ?
23. ### Dynamic pressure along a duct

In an air supply duct after the fan static pressure is maximal directly after the blades and is zero at the duct outlet, volume flow is minimal after the blades, maximal at the outlet. mass flow is equal at all points, speed of air constituents is minimal after the blades (where air is being...