Water Clock

What you need:

• Paper or Styrofoam cup
• Plastic two-liter bottle
• Watch or clock with a second hand
• Pen or pencil
• Ruler
• Masking tape 
  

What to do:

1. Help your child cut the top off the plastic bottle about three inches from the top.
2. Stick a length of masking tape on the outside of the bottle, from the top to the bottom in a straight line.
3. Now push a small hole through the bottom of the cup with your pencil or pen. Fit the cup snugly into the top of the plastic bottle.
4. Get ready with your timer, then pour water into the cup. Start timing immediately. Keep the cup halfway full, so the water runs out steadily.
5. One person must watch the time, while another marks the tape. When 30 seconds have gone by, mark the water level on the tape. Do this every 30 seconds for five minutes. Are the marks on the tape evenly spaced?
6. Put another piece of tape on the bottle, right next to the first one. This time, mark the water level at one-minute intervals. Do this for five minutes. Do your marks match up with marks from the first test? Do you think this is an accurate way to keep time?