upgrade

🔋college physics i – introduction review

Viscous Fluid

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

A viscous fluid is a fluid that has a high resistance to flow, exhibiting a high viscosity. This resistance to flow is due to the internal friction between the fluid's molecules, which creates a drag force that opposes the motion of objects moving through the fluid.

5 Must Know Facts For Your Next Test

  1. Viscous fluids, such as honey or motor oil, have a higher resistance to flow compared to less viscous fluids like water or air.
  2. The viscosity of a fluid can be affected by factors such as temperature, pressure, and the fluid's composition.
  3. Viscous fluids are often used in applications where a high resistance to flow is desirable, such as in lubricants, hydraulic systems, and certain types of paints and coatings.
  4. The motion of an object through a viscous fluid is characterized by a balance between the viscous drag force and other forces, such as gravity or buoyancy.
  5. The terminal velocity of an object falling through a viscous fluid is determined by the balance between the viscous drag force and the object's weight.

Review Questions

  • Explain how the viscosity of a fluid affects the motion of an object moving through it.
    • The viscosity of a fluid plays a crucial role in the motion of an object moving through it. Fluids with higher viscosity, such as viscous fluids, exert a greater drag force on the object, which opposes its motion. This increased drag force causes the object to experience a slower acceleration and a lower terminal velocity compared to if it were moving through a less viscous fluid. The viscous drag force is directly proportional to the fluid's viscosity, the object's size, and its velocity relative to the fluid.
  • Describe how the temperature and pressure of a viscous fluid can affect its viscosity and, consequently, the motion of an object within it.
    • The viscosity of a fluid can be influenced by changes in temperature and pressure. Generally, as the temperature of a viscous fluid increases, its viscosity decreases, and as the pressure increases, the viscosity also increases. These changes in viscosity can significantly impact the motion of an object moving through the fluid. For example, if the temperature of a viscous fluid increases, the object will experience less drag force, allowing it to accelerate more quickly and reach a higher terminal velocity. Conversely, if the pressure of the fluid increases, the object will encounter greater drag force, resulting in a slower acceleration and a lower terminal velocity.
  • Analyze how the principles of Stokes' law can be used to determine the properties of an object moving through a viscous fluid, and explain the limitations of this law.
    • Stokes' law provides a mathematical relationship between the drag force experienced by a small, spherical object moving slowly through a viscous fluid and the object's size, the fluid's viscosity, and the object's velocity. By applying Stokes' law, one can determine properties of the object, such as its size or mass, or properties of the fluid, such as its viscosity, based on measurements of the drag force and other variables. However, Stokes' law has limitations, as it is only valid for small, spherical objects moving at low velocities through the fluid. At higher velocities or for objects of different shapes, additional factors must be considered, and more complex models may be required to accurately describe the motion of the object in the viscous fluid.