The amount of water pushed aside or “displaced” by an object equals the amount of force that the water pushes upward on the object. That means that objects that are heavy for their size sink; objects that are light for their size float. We say that objects that are heavy for their size are “dense”.
The ball of foil and the penny have the same weight as the flat foil and penny. However, the ball of foil takes up a smaller amount of space—it is heavy for its size. Gravity pulls the dense foil ball down.
The flat foil takes up a lot of space (or surface area) on the water. It pushes aside (or displaces) a lot of water—it is light for its size. The water pushes up on the foil with an equal amount of force—enough to keep the foil (even with pennies on it) from sinking.
A big boat floats while a car sinks. Both are heavy objects, but the boat is designed in such a way that it pushes or displaces a lot of water—enough that the force of the water pushing up on the boat keeps it from sinking.