first of course you will need a grape. some work better than others.make sure the grapes aren't cold or it won't work.
Full materials list-
Step 2: Step 1 Prepairing the grape
First slice a thin piece of the top.
Step 3: Step 2
Then cut the grape down the center "pic 1" make sure you do not cut all the way through the grape. Next put the grape in the microwave "pic 2"
Step 4: THE TEST!!!!!!!!!!!!
Place cup over the grape.make sure that air is not completely restricted. IMPORTANT NOTE-change the cup about every 2 to 3 tests or it will explode.(I speak from experience). Then put it in for about 10 to 15 seconds (depending on your microwave). And finally nuke it,i love doing this experiment its fun easy and you don't need a lot of materials. it may take a couple of tries and couple different types of grapes. Here is proof that i have done this experiment. http://www.youtube.com/watch?v=QwzmYHy9Hhc