Hi Mostafa,

In addition to the activity you originally reviewed when asking your question, here is another simple science project related to the Greenhouse Effect (from the California Energy Commission):
http://www.education.com/reference/article/Ref_Greenhouse_Effect/

Here is one from ScienceBuddies.org that is harder..
"Is it Getting Hot in Here? Investigate the Greenhouse Effect"
http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvSci_p047.shtml

If neither of those interest your son, here is a listing of Global Warming/Greenhouse Effect projects you can review (scroll to middle of page for 5th grade projects):
http://www.juliantrubin.com/fairprojects/environment/globalwarming.html

For background research, here are some articles you might review and discuss with your son:

What is the Scientific Method?
http://www.education.com/reference/article/Ref_What_Scientific/

Get Your Kids Global Warming Savvy
http://www.education.com/magazine/article/Global_Warming_Savvy/

I hope these resources are helpful to you and your son.

add some soil in the jar,add earthworms in it,plant or put a small plant in it and sprinkle some water in it and close the jar and observe it regularly so by this      experiment you will get your answer.