Different densities have to have a reason - different pressure and/or humidity etc. If there is a different pressure, there is a mechanical force that preserves the pressure difference: think about the cyclones that have a lower pressure in the center. The cyclones rotate in the right direction and the cyclone may be preserved by the Coriolis force.
If the two air masses differ by humidity, the mixing will almost always lead to precipitation - which includes a phase transition for water etc. It's because the vapor from the more humid air mass gets condensed under the conditions of the other. You get some rain. In general, intense precipitation, thunderstorms, and other visible isolated weather events are linked to weather fronts.
At any rate, a mixing of two air masses is a nontrivial, violent process in general. That's why the boundary is called a "front". In the military jargon, a front is the contested frontier of a conflict. So your idea that the air masses could mix quickly and peacefully - whatever you exactly mean quantitatively - either neglects the inertia of the air, a relatively low diffusion coefficient, a low thermal conductivity, and/or high latent heat of water vapor. A front is something that didn't disappear within minutes so pretty much tautologically, there must be forces that make such a quick disappearance impossible.
Answer:
5.A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. This uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.
6.The Nazca plate is an oceanic plate, while the South American plate is continental. The fast moving Nazca plate is moving east towards the South American plate at a downward angle and converging. This process is called subduction, resulting in frequent earthquakes & production of the Andes Mountains.
7.The Nazca plate forms the southeastern part of the Pacific plate. The Nazca and the Pacific plate share both divergent and transform type of plate boundary. The Pacific and the Nazca plate are separating at an increasing rate of about 122-142mm/year.
8.Convection currents in the mantle and in the ocean are similar because they both are responsible for the shaping the Earth's surface. Two forces are behind the movement of Earth's huge land masses. Due to combined action of convection currents and gravity, Earth's plates are in constant motion.
Explanation:
The distance is 30 km and the displacement is 22.4 km North East
Answer:
,Assume that the average volume of an adult human body is one-tenth
cubic meter (0.10 m) and that there are two billion (2.0 x 109)
adults in the world.
a. What would be the total volume of all the adults in the world?
b. Compute the length of one edge of a cubic container that has a
volume equal to the volume of all the adults in the world.
Answer:
The bullet's initial speed is 243.21 m/s.
Explanation:
Given that,
Mass of the bullet, 
Mass of the pendulum, 
The center of mass of the pendulum rises a vertical distance of 10 cm.
We need to find the bullet's initial speed if it is assumed that the bullet remains embedded in the pendulum. Let it is v. In this case, the energy of the system remains conserved. The kinetic energy of the bullet gets converted to potential energy for the whole system. So,
V is the speed of the bullet and pendulum at the time of collision
Now using conservation of momentum as :
Put the value of V from equation (1) in above equation as :
So, the bullet's initial speed is 243.21 m/s.
