One of the best visual science presentations for an 8-year-old is a volcano. It utilises a chemical reaction to simulate a volcanic eruption. There are a few options for volcano design and lava type, as well as an underwater version of this science project. A volcano for an 8-year-old's science project can be made with little difficulty.
Poster Board Volcano
For the easiest of the volcano projects you simply need to start with a 591ml glass or plastic soda bottle. Lay it mouth-down in the middle of a poster board. Trace around the bottle's mouth with a marker. Cut a straight line from the edge of the poster board to the circle that you just drew in the middle and cut the circle out. Take the two cut edges and overlap them to form a cone, then tape them together. Trim a bit at a time off the bottom of the cone until you have a cone that fits perfectly over the bottle when it is resting on the table right side up. Fill the cone with balled-up newspaper around the bottle to make it more stable. Place it on a base, such as a cardboard box bottom, with a two- or three-inch lip on all sides. Colour the cone to your liking.
Play Dough or Clay Volcano
Create a base that can keep the mess contained, such as the bottom of a cardboard box with a two- or three-inch lip on all sides. Build your volcano by forming a play dough or clay mound. Place a 567gr bottle in the middle of the base and form the play dough or clay around it, forming a cone-shaped volcano.
Create a base with the bottom of a box with a two- or three-inch lip on all sides. Place a 567gr bottle in the middle of the base and form a bunch of crumpled-up newspaper around the base of the bottle, taping it down to stabilise it. Mix equal parts water and white PVA glue and use the mixture to dip square strips of newspaper in and stick several layers of the strips around the bottle and newspaper. Let the volcano dry before painting it.
For each of the above methods, fill the bottle about three-quarters full with water and add two or three tablespoons of baking soda. Put four or five drops of dish detergent in the bottle. In a separate bottle mix four or five tablespoons of white vinegar with a few drops of red-and-yellow food colouring. Dump the vinegar into the volcano, then sit back and watch the marvels of a volcanic eruption.
Mentos and Soda Lava
An alternative "lava" involves filling the bottle with a carbonated soda, such as Dr. Pepper, Pepsi or Coke. Drop three or four Mentos candy's in all at once and step back. The result is a violent eruption, which causes an enormous mess.
In a large-mouthed but skinny glass jar, build a play dough or clay volcano around a small container, such as an old film canister, leaving the opening unobstructed. Mix the vinegar with the red-and-yellow food colouring and fill the container to the top of your volcano. Fill the container with vegetable oil, taking care not to spill the vinegar out of the volcano and so that it is about four or five inches above the top of the volcano. Mix the rubbing alcohol with a blue food colouring and pour it into the jar as well. When everything has settled, the three liquids will be separate. Mix one or two tablespoons of baking soda with just enough water to create a thick past. Take small globs of the paste and drop them into the volcano to witness the underwater eruptions.