a U-tube is a glass tube shaped in the form of letter "U" which can be used as a manometer, and is used in measuring the pressure of liquids.
it is a physical object...
A burner tube is a metallic tube with two opposite air holes near its lower end.it is screwed to the nipple and carries the air regulator
lagayan ng test tube,hehehe
Um... to clean test tubes! Test tubes are used very often to perform experiments on a small scale, hence they need to be cleaned quite often.