Physical buoyancy force analysis, physical buoyancy problem

Of course, you can think so. Floating on the surface of the water is called floating, and when it is immersed in water, it is called levitation when it sinks to the bottom. At this time, the gravitational force on them is equal to the buoyant force.

On the second question. There is pressure on the inside of the water in all directions. Water can be divided into two layers, the upper layer has a pressure on the lower layer, and acts on a force surface, so that the pressure is generated. And because the force is reciprocal, the lower layer also has pressure on the upper layer.

Suspension and float when f=g

When sinking to the bottom, although it is stationary, it is g = f + fn (support force) because the wooden block is not completely in contact with the water at the bottom, so it will be subjected to an upward pressure from the water, and the buoyancy is generated by the pressure of the lower part of the object - the pressure of the lower part, which is generated by this pressure difference.

Special case: If the object is completely not in contact with the water at the bottom of the water, then there is no pressure difference, it is not buoyant and generally not completely out of contact with the bottom.

So when the object is at rest when it sinks to the bottom, the force is balanced g=f+fn (supporting force) The molecules of the liquid are in constant motion and are not fixed there like solids, so there is pressure in all directions.

When floating and levitating, the object is subject to only one gravitational force and one upward buoyant force, and since it is at rest, the two forces are balanced, and the buoyancy force is equal to the gravitational force; But when sinking to the bottom, it is subjected to gravity, and upwards is supported by the contact surface and buoyancy, so buoyancy plus support is equal to gravity.

Water is pressurized in all directions.

When you are not in contact with the bottom of the water, you can think of it as [special cases are not excluded] because it is supported after sinking under the water.

When floating on water and suspended in water, buoyancy is equal to gravity. When it sinks to the bottom of the water, the net force of the object is zero, which is good. But at this time, it is not only buoyancy that overcomes the gravitational force of the object, but also the supporting force of the bottom of the container.

no no no no!

When the object is suspended in the water and sinks to the bottom, then the water must be topless, then v object = v row.

Since the density is equal, only the volume of boiling water determines the buoyancy.

So, in this problem, if g are equal, then the amount of buoyancy is only related to the volume of water it distributes, not to the state.

Otherwise, if it sinks to the bottom, it may also be a balance of support force plus buoyancy and gravity. In other cases, it can.

Categories: Education Science >> Admission >> High School Entrance Examination Question Description:

Place an overflow cup on the left plate of the balance and fill the cup with water until the water flows out of the overflow, the outgoing water can flow into the container outside the balance plate, put an appropriate amount of weight on the right plate of the balance to make the balance in balance, as shown in the figure. In the following cases, the balance can still be balanced.

a.Put a wooden block with a mass of m grams in a cup.

b.Put a piece of iron with a mass of m grams in a cup.

c.Hold a piece of iron with a mass of m grams with a thin wire and place it in a cup until the iron is completely submerged in water, but does not come into contact with the bottom or wall of the cup.

d.Place a piece of iron in the cup with a mass of m grams, and at the same time add m grams of weight to the right plate of the scale. Analysis: c

The gravitational force of the iron block is known to be counteracted by the pulling force and the buoyant force.

Suspension and float when f=g

When sinking to the bottom, although it is stationary, it is g = f + fn (support force) because the wooden block is not completely in contact with the water at the bottom, so it will be subjected to an upward pressure from the water, and the buoyancy is generated by the pressure of the lower part of the object - the pressure of the lower part, which is generated by this pressure difference.

Special case: If the object is completely not in contact with the water at the bottom of the water, then there is no pressure difference, it is not buoyant and generally not completely out of contact with the bottom.

So when the object is at rest when it sinks to the bottom, the force is balanced g=f+fn (supporting force) The molecules of the liquid are in constant motion and are not fixed there like solids, so there is pressure in all directions.

Levitation and floating.

When f=g sinks to the bottom, although it is stationary, it is g=f+fn (support force) because the wooden block is not completely in contact with the water at the bottom, so it will be subjected to an upward pressure from the water, and the buoyancy is generated by the pressure of the lower part of the object - the pressure of the lower part, which is generated by this pressure difference.

Special case: if the object is underwater.

No contact with water at all.

Then there is no pressure difference, and it is not subject to buoyancy.

In general, it is not completely devoid of contact with the bottom of the water.

So the object is at rest when it sinks to the bottom.

Balanced forces. g = f + fn (support).

The molecules of a liquid are in constant motion and are not fixed there like solids, so they are under pressure in all directions.

Suspension and float when f=g

When sinking to the bottom, although it is stationary, it is g = f + fn (support force) because the wooden block is not completely in contact with the water at the bottom, so it will be subjected to an upward pressure from the water, and the buoyancy is generated by the pressure of the lower part of the object - the pressure of the lower part, which is generated by this pressure difference.

Special case: If the object is completely not in contact with the water at the bottom of the water, then there is no pressure difference, it is not buoyant and generally not completely out of contact with the bottom.

So when the object is at rest when it sinks to the bottom, the force is balanced g=f+fn (supporting force) The molecules of the liquid are in constant motion and are not fixed there like solids, so there is pressure in all directions.

Let's start with the object: the object is definitely subject to gravity and buoyancy, and possibly by the pull of the rope. (If gravity is equal to buoyancy, then it is not subject to tension).

Re-analysis of the cup: The cup is definitely subjected to the pressure of gravity and water on the cup. May be subject to rope pull.

The direction of gravity is straight down, the pressure of the water is straight down, and the rope pull is straight up.

At this time, the levitation is in equilibrium, and the gravitational and buoyancy are balanced.

Are you referring to the cup that holds the water?

If so, the cup filled with water is subjected to its own gravity, the pressure of the water, the rope tension (possibly, to be discussed on a case-by-case basis) and the support force if placed on a horizontal plane.

For the blocks in the cup are subject to the buoyancy of the water, the pull (if the buoyancy force is greater than its gravitational force), and the gravitational force.

The direction of the force I think you understand.

The side wall of the quilt is subjected to pressure, and the bottom of the cup is subjected to the downward pressure of the water and the upward pull of the object (the pull of the upward buoyancy of the object).

The crux of the matter is the volume of the ice cubes when they are melted and the volume of the ice cubes as they float in this other liquid.

The denser the liquid, the smaller the volume of the ice will be discreted. Finally, when the ice melts into water, in addition to filling the space it originally discharged, the total liquid level rises, otherwise it falls. If the liquid is water, then just fill it up, and the liquid level will not change.

In the case of alcohol, because the ice cube is sunk in it, and the volume of the ice cube after turning into water is reduced (the density of ice is less than that of water, the volume of ice to water is reduced), so the volume of the total liquid is also reduced.

The water does not change, the salt water rises, the alcohol falls, the mercury rises.

The height remains the same, if not miscible at all.

The water does not change, the mercury increases, the alcohol decreases, and the salt water rises.

Water and mercury are insoluble, obviously after adding water, due to the small density of water, the water floats on the mercury, and the amount added will rise as much as possible, so the liquid level containing mercury rises.

When you put ice in the water, the ice turns into water, and when you add water to the water, you can raise as much as you want, just like when you add a hot water bottle.

Add water to the alcohol surface, the alcohol is diluted and the mass increases, but the density is decreasing, from P=M V, M increases, P decreases, indicating that V is also increasing, assuming that the container is a cylinder, V=SH, S is unchanged, to increase V, then H increases, indicating that the liquid level of this container is also rising.

Diluting alcohol and diluting salt water is a reason, and the liquid level is also raised.

Answer, the buoyancy he is subjected to is the gravitational force that overflows the alcohol, and the result is, the cow, can be remembered (for a container with a full tank), thank you.

The mass of the wooden block is (50) kg

The density of the block is ( ) Take 20kg, then the volume of the block exposed to the water is (20 dm3).