Final answer:
Density differences in sugar and salt are a result of crystal size and packing density. For pennies, density is influenced by their copper and zinc content. With aluminum foil, density and shape determine sinking or floating in water.
Step-by-step explanation:
The experiment you're describing involves comparing the densities of sugar and salt. To find out which substance has greater density, you would measure a specific volume of each and weigh them to determine the mass. You would then calculate density by dividing these masses by the volume you used. Densities can differ due to the size and shape of the crystals and how closely they pack together.
In general, the density of a substance is defined as its mass per unit volume. The question seems to suggest a comparison between groups of pennies, which could refer to their composition. Pre-1982 U.S. pennies are made of 95% copper and 5% zinc and post-1982 pennies are made of 97.5% zinc and 2.5% copper with a thin copper plating. Copper has a higher density than zinc, hence older pennies are denser than newer ones.
When it comes to the aluminum foil experiment, because the density of aluminum foil is greater than that of water, a tightly rolled ball of foil should sink. However, the shape can influence whether it sinks or floats due to the displacement of water and the air trapped inside the ball; manipulating the shape can change its buoyancy.