One fun science experiment for adults demonstrates how heat causes things to expand and cold causes things to get smaller. To begin, place an empty soda bottle in the freezer for one hour. Take it out of the freezer. Wet the top of the bottle with water. Put a penny on the top of it so that it covers the opening to the bottle. Make certain that there are not any leaks. Place the bottle in the freezer again for one hour. Remove the bottle from the freezer and hold it with both hands, one on each side of the bottle. Hold onto the bottle and wait for about one minute. The penny will blow off of the top with quite a bit of force.
Another science experiment that adults can do is one that demonstrates what happens when clouds form in the sky. Put about 2 tbsp. of water in a medium-sized glass jar. Place a latex glove into the jar with the fingers of the glove pointing down. Stretch the top of the glove, the mouth of it, over the top of the glass jar. Gently insert your hand into the glove. With your hand still in the glove, quickly pull your hand out of the jar. Take the glove off of your hand. Light a match and drop it into the glass jar. Place the glove back into the jar and wrap the mouth around the top again. Put your hand into the glove again and then quickly pull it out. The clouds will form when you put your hand into the jar and disappear when you pull it out.
An entertaining science project for adults is making a tornado in a jar. Take a medium-sized glass jar and fill it with water. Add approximately 1 tbsp. of dishwashing liquid. Put the lid tightly on the glass jar. Shake the jar, turn it upside down and create bubbles. Swirl the jar around, which creates a mini whirlpool that looks like a tornado.