  After thrown onto a solid substrate, very soft spherical gels bounce
repeatedly. Separate rheological measurements suggest that these balls can be
treated as nearly elastic. The Hertz contact deformation expected in the static
(elastic) limit was observed only at very small impact velocities. For larger
velocities, the gel ball deformed into flattened forms like a pancake. We
measured the size of the gel balls at the maximal deformation and the contact
time as a function of velocities for the samples different in the original
spherical radius and the Young modulus. The experimental results revealed a
number of scaling relations. To interpret these relations, we developed scaling
arguments to propose a physical picture.
