# Tag Info

### Displacement of water - Archimedes' principle

If you consider two different boxes with the same dimension (assume cube for simplicity), the floating object will displace less water. This means that a less buoyant force is acting on it. However, ...
• 73

### What is the microsopic reason why hot air rise?

You are getting a macroscopic explanation because this is a macroscopic effect. Microscopically, air molecules move in random directions with approximately the speed of sound. (For mean thermal ...
• 71.5k

### Is the pressure-gradient force that causes hydrostatic equilibrium entropic, contact, or both?

Two thoughts occur to me. First, we can model an ideal gas by allowing that there are short-range repulsive forces between molecules (the 'hard spheres' model), and the molecules themselves take up a ...
• 47.1k
Accepted

### Collecting gas over water -- is the textbook explanation wrong?

You are correct. The atmospheric pressure equals the pressure due to the water column plus the pressure due to the collected gas and water vapour. $$P_{gas} = P_{atm} - P_{column} - P_{w.vap}$$ You ...
• 2,091
1 vote
Accepted

### A question on Hydraulics from a 19th century book

Take a strong glass tube about three feet in length, and tie over one end a piece of well-soaked bladder. When thoroughly dry, . . . . The dry bladder provides a stiff and air-tight seal at one end of ...
• 77.9k
1 vote
Accepted

### Resulting height of displaced fluid after adding a floating object

Your mistake is assuming $V_d$ is a cylindrical ring. $V_d$ is just a cylinder $$\frac {\pi D^2h_d}{4}$$
• 604
1 vote

### What is $V$ in Buoyant force $V\rho g$?

V is the volume of fluid displaced. If the iron block has mass $M$ and we assume that the box does not sink after its introduction then there must be an additional $Mg$ buoyant force supplied, which ...
• 717
1 vote

### Am I understanding Pascal's law the right way?

If we compare a liquid and a solid in a similar pressure situation, the result can be also the same. Suppose a spherical thick steel container, with a hole for entrance where a piston can be installed....
• 12.3k
1 vote

### What about negative (absolute) pressure in Bernoulli Equation

The Bernoulli equation is derived assuming the fluid is incompressible, which is an idealization even for liquids, and even more for gases. This idealization is valid provided density $\rho$ in the ...
• 28.4k
1 vote

### Size of mercury barometer and effect on its reading

A vacuum must exist above the meniscus of the column so that the mercury can rise above 760mm (or 30 in.) which is what a mercury barometer reads at sea level. In other words, the mercury column ...
• 11

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