What You Need:
- Two large transparent bowls
- Clear plastic tubing long enough to comfortably go from one container to the other (available from a hardware store or aquarium supply store)
- Food coloring for better visibility (optional)
- Large jug of water
- Two surfaces (close together, one lower than the other)
- Clean funnel (optional)
What You Do:
- Ask your child to mix the food coloring into the water in the jug and to pour the water into one of the glasses.
- Two surfaces are needed, with one lower than the other (a table and chair work well). Have your child place the empty bowl on the lower surface.
- Invite her to put the bowl of colored water on the higher level surface and to place one end of tubing into this bowl.
- Ask your child to fill the tube with water, either by pouring from the jug -using a funnel might help, or by sucking it from the glass. (If you're planning on letting your child put her mouth on the tubing, make sure that it's non-toxic!)
- Once the tube is full of water she should quickly plug the open end with her finger. This end of the tube goes into the empty bowl. Ask your child to keep her thumb over the end of the water-filled tube as she makes the transfer.
- Water will "siphon" out of the higher bowl into the lower empty bowl.
- Now, to make the water flow more obviously "uphill." Ask your child to carefully raise the middle part of the tube so that it's higher than the bowl set on the high surface. Another way is to drape the tubing over the back of the chair on which the lower bowl is sitting, so the tube goes up over the chair before entering the lower bowl. Make sure that the ends of the tube stay in the two bowls and that there's still plenty of water in the upper bowl. The water should continue to flow into the lower bowl, even though it has to first go uphill!
The siphon works because of the difference in pressure. The water flows from the higher pressure in the upper bowl to the lower pressure in the lower bowl, yet still goes "uphill" before flowing down. Also, the cohesive nature of water molecules to each other aids the siphoning action.
Now have your child place the full bowl of water on an even higher surface than the table. See what happens! Encourage your child to record her observations when the experiment is varied. With your child, brainstorm other ways a siphon can be used.
Take this activity outside with plastic bowls or buckets!