Densitometer is the use of floating in a liquid condition on the surface of the work, that is to say when the liquid density is measured with a densitometer, it floating in the liquid surface, the floating = G, F gV rho fluid = G, we put the densitometer approximation as cylinder, V = Sh leaching, gSh rho fluid immersion = G, fluid of rho = G/gSh leaching, densimeter, the cross-sectional area of gravity must be, to measure the density of the fluid is inversely proportional to the density meter immersed depth of liquid, namely the densitometer, floating in the liquid surface into the depth of the liquid, the greater the measured liquid density is smaller, conversely, the smaller the immersed depth of the liquid, the greater the density of the liquid under test.
So the scale on the densitometer gets bigger and bigger as you go down.

Usually people making improvised densitometer (on an even thickness of bottom stick around some fine wire, stick on the scale) to compare the density of the fluid size, through the above analysis can be simple conclusion: simple densitometer is immersed in liquid is less, the corresponding fluid density, the greater the on the other hand, the deeper the densitometer immersed in a liquid, the liquid density is smaller.

Example :(yancheng, 2019) xiaoming made a simple densitometer with a drink straw. When it was put into water, the densitometer could not stand upright, and the wire mass in the straw should be (increased/decreased). After improvement, when it was used to measure the density of water and brine respectively, the depth of the straw immersed in the liquid was h1 and h2, then h1 h2.
When using it to measure the density of coke, the straw is “stained” with many small bubbles, the measured density is skewed.

Analysis :(1) xiaoming puts the self-made densitometer into the water. The densitometer cannot float upright, so its center of gravity should be lowered. Therefore, the weight of the wire in the straw should be increased.

(2) The liquid density measured by the densitometer is in a floating state.

So F floating water is equal to F floating brine is equal to G,

If the base area of the densitometer is S, it is impregnated with F float = rho gV = RHO gSh:

Rho gSh1 = rho saline gSh2,

So we know rho < rho saline, so h1 > h2,

(3) When the density of coke is measured with a densitometer, F float = G

F float = rho gV platoon =G, rho =G/gV platoon

When the density of coke is measured, many small bubbles are “dipped” on the straw. At this time, V-row = V bubble +V immersion, that is, V-row remains unchanged and V immersion becomes smaller, that is, the depth of the densitometer immersed in Coke becomes smaller and the measured density becomes larger

The answer goes up by >


  1. (2018 Huaihua) A densitometer was placed into a and B liquid respectively, and its position at rest was shown in the figure.
    If the buoyancy received by the densitometer in liquid A and B is F a, F B, the density of liquid A and B is rho, Rho B.
    The following statement is correct ()

A. > b. >

Rho a < rho B D. Rho > b

The answer C

  1. (Lanzhou, 2018) Put an appropriate amount of iron sand in a flat tube and successively put it into beakers containing two different liquids, A and B, as shown in the picture.
    The following statement is correct ()

The test tube is subject to greater buoyancy in a liquid

The test tube is more buoyant in liquid B

The bottom of the beaker of the armored liquid is subjected to a high liquid pressure

The bottom of the beaker containing liquid B is subjected to a higher liquid pressure

The answer D

A ship came out of the river into the sea

Come up a little bit B.
Down some

Neither rising nor sinking D.
The conditions are insufficient to determine

The answer to A

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