# Tag Info

### Helicopter hover flight question

For this kind of problem, I find it easier to think about momentum than about mass and acceleration. Remember that momentum is mass times velocity, $$\vec p = m\vec v$$ and so Newton's second law ...
• 70.1k

### Why forces exerted by fluids, inside or outside, are always perpendicular?

Why all fluids exert only perpendicular force. Why not parallel? Fluids certainly can and do exert parallel forces. Such forces are called shear, and the defining feature of a fluid is that it ...
• 64.3k

### Why does Torricelli's law seems to fail when water speeds up after I put my finger in a hose?

What you have given as toricelli's law is a general simplication. The actual law is stated as this: $$v = \sqrt\frac{2gh}{1-\frac{a^2}{A^2}}$$ Here $a$ is the area of the smaller hole and $A$ is the ...
• 693
1 vote

### Would water flow in the following system?

Short answer: it depends! Longer answer: If the temperature of the water in the tank is uniform and the peltier is able to reduce the temperature of the water, ther will be a flow of water. At least ...
• 380
1 vote

### Helicopter hover flight question

When analysing a fan, propeller or engine which isn't moving, the air which is being sucked through the rotor starts far away and not moving. Air is drawn in from all around, so the area far away is ...
• 308
1 vote
Accepted

### Does convection occur in microgravity due to pressure gradient?

In a microgravity environment, the gas will heat and expand uniformly in all directions. Due to diffusion and thermal conduction (followed by eventual thermal equilibrium of the whole region), there ...
• 24.8k
1 vote

### Is incompressible fluid flow isentropic?

No. For a viscous fluid, flow isn't isentropic. Viscosity dissipates kinetic energy as heat, generating entropy.
• 3,239

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