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Why does Silly Putty bounce during a quick impact but flatten when left on a table?

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Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).
mechanics of solids Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).

Silly Putty is a type of bouncing putty, which is a viscoelastic material. Its behavior depends on the rate at which force is applied, a characteristic common in many polymeric solids.12

When you subject the material to a quick impact, the high strain rate causes it to respond elastically, allowing it to bounce like a solid. Conversely, when left on a table, the material is subjected to a constant, low-level load over a long period. Under these conditions, it exhibits viscous flow, causing it to deform and flatten out over time. This dual behavior is a hallmark of viscoelasticity, where the material's responseā€”whether it acts more like a solid or a fluidā€”is determined by the time scale of the applied stress.123