Question

Why does pouring hot water over a tight jar lid loosen it?

Hot water makes the metal of the jar lid expand, which makes the cover loose．

Most objects expand when heated because they are made up of molecules．Heat makes molecules move faster．The hotter the molecules become, the faster they move and the more space they need．

This explains why we hear a click as we travel by train, or a gentle thump as we drive on a concrete highway．The clicks and thumps tell us that we are passing over expansion joints put in to allow room for the metal rails and the concrete to expand．These joints prevent the rails and the road from changing their shapes as they expand under the hot sun．Like the molecules of the jar lid, the molecules of these materials need more space when they are hot．

1．Pouring hot water over a jar lid will _________．

A． make it fit very tightly                      B． make it less tight

C． not affect the lid itself in any way             D． make the jar expand

2．This happens because the hot water __________．

A． heats whatever is inside the jar                   B． causes the jar to grow smaller

C． makes the lid slightly bigger                       D． all of above

3．An object is made up of molecules that move _________．

A． if the object becomes very hot                    B． whenever hot water is poured over it

  C． all the time                                               D． only when the object is expanding

4．Objects expand when they are hot because hot molecules _______．

A． move faster                                 B． make up more room

C． move slowly                                 D． both A and B

Answer 1

BCCD