Experimental steps: ① the gravity of pebbles in the air is g measured by spring dynamometer;

(2) Immerse the stone in water and read the indicator of the spring dynamometer as f1;

③ Immerse the stone in vegetable oil, and read the indicator of the spring dynamometer as F 2.

The mathematical expression of vegetable oil density: ρ = ρ water.

Experimental steps:

(1) Tie the pebbles with fine iron wire, and measure the gravity g of the pebbles with a spring dynamometer.

(2) Pour a proper amount of water into the glass, hang the pebbles with a spring dynamometer, let all the pebbles immerse in the water, and read the reading f1of the spring dynamometer; The gravity of boiling water discharged by small stones is g water =G-F 1,

③ Pour a proper amount of vegetable oil into the glass, hang small stones with a spring dynamometer, let all the small stones immerse in the vegetable oil, and read the reading F2 of the spring dynamometer; Gravity G oil =G-F 2, and G water = ρ water gV row, that is, G-F 1 =ρ water gV row, G oil =ρgV row, that is, G-F 2 =ρgV row, and small stone volume V=V row, then the mathematical expression of vegetable oil density is ρ = ρ water.