Analysis of test questions: This experiment is based on the fact that when an object floats, the buoyancy is equal to gravity, and the increased gravity is equal to the increased buoyancy, combined with Archimedes' principle to carry out experimental exploration.

experimental purpose: to measure the density of oil

experimental equipment: a plastic beverage bottle with a cylindrical neck, a bucket of water, a scale, oil and several stones.

experimental principle: two-force balance

experimental steps:

(1) cut off the upper part of the beverage bottle and keep the cylindrical part in the middle.

(2) Measure the height h 1 of the bottle exposed to the water.

(3) Inject some oil to be measured into the bottle and measure the thickness of the oil layer on the water surface in the bottle.

(4) Put the bottle into the barrel again and measure the height h 2 of the bottle exposed to the water surface.

So

Using the above method to measure the densities of two kinds of oil respectively, the expression of oil density is:

So the answer is: scale; Two forces balance (floating condition); Measure the height of the bottle above the water, h 2? ;

Comments: When an object floats, the buoyancy of the object is equal to the gravity of the object. As the gravity of the object increases, the buoyancy also increases, and the increased buoyancy is equal to the increased gravity.