Science Buddies: "Ask an Expert"

I'm doing this experiment:

https://www.sciencebuddies.org/science- ... p015.shtml

The project states that 50mL of gelatin in a Petri dish should fill it about halfway... Every Petri dish I can find only holds about 10mL of liquid?! What am I missing?

EDIT: The Materials list calls for dishes 100 mm diameter x 15 mm deep, how can those hold >50mL???

Hi,

When I use disposable 100 mm plastic Petri dishes I pour about 25 mL of agar into each dish which fills it a little less than half full. I can pour 20 plates from 500 mL of agar.

I did the calculation based on the volume of a cylinder which is pi x height x radius squared:

3.1514 x 1.5 cm x 25 cm squared = 118 cubic cm or 118 mL

Are you sure your dishes are 10 cm in diameter? They have to hold more than 10 mL. Did you try pouring in 50 mL of water just to see how high up it comes?

The experiment has you weighing the dishes with the Jello and measuring its height so it would be better to have the same volume in each dish. You don't have to use 50 mL, but do measure the volume and pour the same amount of Jello into each dish.

Sybee