Make a model of a sand clock which can measure a time interval of 2 minutes (Fig. 13.17).

1. Take one plastic cup and place it in upside down on a table. Put the other cup on the top of the first one so that the bottom parts of both cups touch each other.

2. Place two lids on the cups and make holes into them. And then invert one cup one another.

3. Measure the sand and put on top of one cup timer. Allow the sand to pass through the holes.

4. Place the cup timer on top of plate and note down the time taken by the sand to pass through the bottom of the timer.

5. Adjust the amount of sand until the time taken by it is 2 minutes for all the sand to pass through the bottom of the timer.