Question

Which of the following is a the Bingham plastic fluid?

• A. Water
• B. Corn flour
• C. Starch Suspension
• D. Toothpaste

Hint:

Key giveaway for Bingham plastics: They "hold their shape" until you push them. Think of drilling muds, paint, and toothpaste.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify a "Bingham plastic" fluid from the provided list. A Bingham plastic is a type of non-Newtonian fluid that requires a minimum shear stress (yield stress) to be applied before it begins to flow.
Key Formula or Approach: The Bingham model is: \[ \tau = \tau_0 + \eta_p \gamma \] Where \(\tau\) is shear stress, \(\tau_0\) is yield stress, \(\eta_p\) is plastic viscosity, and \(\gamma\) is shear rate.

Step 2: Detailed Explanation:

• Fluids are classified based on their response to shear. Water is a Newtonian fluid; its viscosity is constant.

• Corn flour and Starch suspensions are typically shear-thickening (dilatant) fluids. Their viscosity increases with the rate of shear.

• A Bingham plastic behaves as a rigid body at low stresses but flows as a viscous fluid once the "yield stress" is exceeded.

• Toothpaste is a classic example. When you tip a tube of toothpaste, it does not flow out due to gravity. You must squeeze the tube (apply yield stress) to force the paste to flow. Once flowing, it behaves somewhat like a linear fluid.

• Other examples in the food industry include ketchup, chocolate mass, and certain margarines.

Step 3: Final Answer:
Toothpaste is the correct example of a Bingham plastic fluid.