# Recent content by Yuri B.

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

My scooter powered by 24V 7AH battery, the (brushed) motor 250 W runs 4 mi. I have added more 7AH batteries (so 14AH now), so am having now 8 mi range. But how on earth anything powered 48V 4.4AH, the (even brushles) motor 700W could run 10 mi (let alone 13mi) ?
2. ### 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 ?
3. ### Mercury in air

Exposure or Absorption and the Crucial Question of Limits for Mercury Derek W. Jones, PhD, FIM, CChem., FRSC(UK), FBSE ABSTRACT
4. ### Mercury in air

Who knows what is safe amount of inorganic mercury breathed daily ?
5. ### 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...

Thank you.
7. ### Water density / volume

But will % of expansion = % of decrease in density ?
8. ### Water density / volume

Let it be it, but I refer to the exactly 2 points (on the "curve") between which there is the 4% decrease in density for, as it seems, 2% increase in volume Square root ?
9. ### Water density / volume

I mistakenly put it otherwise so, more precisely - according to the reference - it should be : 0.999808 at 0 °C 0.958593 at 100 °C - about 4 % of the initial value But the volume will increase just 2 % Maybe there is square root relation ?
10. ### 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...
11. ### Measurement points for fan performance curve

Volume. Should turbulence in some points of the duct add some dynamics to static pressure being measured by the probe placed right perpendicular to flow ?
12. ### 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 ?
13. ### Homomorphism between Lie groups

It's mathematics not physics !
14. ### Water as coil core

I need to empty an actually water glycol-system but I do not want to remove all but to a certain level. It would be an improvised level sensor.
15. ### 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 ?