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JordanWe are so used to our atmospheric pressure down here on earth that we tend to think of it as the absolute norm; more often we don't think of it at all. The truth is that zero pressure, the theoretical pressure in deep space, or very close to it, is the situation in vastly more of the universe's volume than planetary pressure. Zero pressure is the standard. In space, there are particles and some mind bogglingly thin gases, but for most applications we could think of, these things would produce negligible pressure on an object. Earth has atmospheric pressure only because earth has an atmosphere, along with sufficient gravity to hold it down, and magnetic field properties that prevent our atmosphere from being stripped off little by little by solar winds.
At sea level on average, the pressure of our atmosphere will push Mercury up into a vacuum tube about 760mm. There are several other ways to think about and to measure atmospheric/barometric pressure.
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What is the Difference between an active earth pressure and passive earth pressure?
When the wall moves away from the backfill, the earth pressure on the wall decreases. This minimum pressure is called active earth pressure. On the other hand if the wall moves towards the backfill, the earth pressure increases. This maximum pressure is called passive earth pressure.
What do you mean by step and touch potential and it's standard value?
Step Potential is the potential Difference between two points on the earth's surface, separated by distance of one pace, that will be assumed to be one meter in the direction of maximum potential gradient (IS 3043) Touch Potential is the potential difference between a grounded metallic structure and a point on the earth's surface separated by a distance equal to the normal maximum horizontal reach, approximately one meter. (IS 3043)
What is the difference between digital terrain model and digital elevation model?
DTM = Digital Terrain Model is a digital representation of the sloped contour surface of the earth. Surface features, such as man-made objects and vegetation, are not included. DEM = Digital Elevation Model is a digital representation of the sloped contour surface of the earth. Elevation data is included, along with surface features such as man-made objects and vegetation.
What is the difference between a radar altimeter and a barometric altimeter?
Radar altimeter gets altitude information by bouncing a radio wave off the surface of the Earth and determines the aircrafts altitude by measuring the length of time it takes for the signal to return. Barometric altimeters get altitude information by measuring the barometric air pressure outside the aircraft. Barometric pressure decreases as altitude increases. Radar altimeters will give altitude above ground level while barometric altimeters give altitude above sea level.
What is the difference between insulation resistance and earth resistance?
insulation resistance can be measured by means of megger, with built in d.c generator. It is measured between the conductor and the earth. earth resistance can be measured by means of earth resistance tester. For good effective earthing, th earth resistance should be of order 0.5 ohm
