The world's oceans are filled with saltwater, but icebergs are made of freshwater. For an iceberg-themed experiment, melt ice in different concentrations of saltwater to see how the concentration of salt in the water effects melting time. Another experiment would be to track the rate of temperature change when ice is melted in pure water and when it is melted in saltwater.
Common sense tells us that hot water would freeze slower than cold water. But is that true? Try making ice by starting with different temperatures of water. It is important to make the ice in identically sized receptacles to guarantee the accuracy of the experiment and to open the freezer door at consistent intervals to check for freezing. Make a graph showing how long it took for ice to form from the different temperatures of water. The science behind the surprising result of this experiment is called the Mpemba effect.
Nothing is more disappointing on a picnic than discovering that the ice in the cooler has all melted and the refreshments have warmed. Use different methods of preserving ice to see how well each one works. Besides coolers and the old-fashioned method of burying ice in sawdust, aluminum foil will add a twist to the experiment. Wrap one ice-cube container in aluminum foil, which will reflect light and heat away from the ice within, and see how the different methods measure up. Use any insulating material available, from a sweater to housing insulation.
There is a saying that most of an iceberg is submerged underwater. Experiment with different shapes of ice and see how they float. You can make different shapes of ice using things around the house -- food storage containers for plain blocks, a funnel plugged with a cork to make a cone, or put some water at the bottom of a freezer bag to make a long cylinder. Observe how much of the different shapes are above and below the water line. Float different materials in the water, such as wood and plastic, to compare floating properties.