Question

Tooth paste is a

• A. Newtonian fluid
• B. Bingham plastic
• C. Pseudo plastic
• D. Dilatant

Hint:

Bingham plastic materials need a minimum yield stress before they begin to flow. Toothpaste is a common example.

Answer 1

The Correct Option is B

Toothpaste does not flow like water under a very small force. It requires a certain minimum stress before it starts flowing. This minimum stress is called yield stress. A Bingham plastic material behaves like a solid until the applied shear stress exceeds the yield stress. After the yield stress is exceeded, it flows like a viscous fluid. Toothpaste is a common example of Bingham plastic behavior. When pressure is applied to the toothpaste tube, the stress becomes greater than the yield stress. Then toothpaste flows out. A Newtonian fluid has constant viscosity. A pseudo plastic fluid becomes less viscous with increasing shear rate. A dilatant fluid becomes more viscous with increasing shear rate. Therefore, toothpaste is: \[ \text{Bingham plastic}. \]