## Fluid Dynamics

Subject: Physics

### Lesson Info

• Notes 4
• Videos 2
• Exercises 0
• Practice Test 0
• Skill Level Medium

#### Angle of Contact and Capillary

￼￼Angle of contact is the angle which is tangent to a liquid surface at the point of contact makes with the solid surface inside the liquid. It's value is acute (900) for liquid which do not wet the walls of container. According to Newton's third law of motion, the tube also exerts on equal and opposite reaction force (R) can be resolved into two compounds i.e Tcosθ which acts vertically upward and Tsinθ which acts horizontally. The horizontal components Tsinθ acting on molecules at the point of contact cancel each other whereas vertical component added up. Hence a liquid experiences a net upward force on the liquid $$F = T\cos\theta \times 2\pi r \dots (i)$$ Learn More

#### Viscosity

Newton studied the viscous force acting between two layers of liquid assuming it flow to be laminated and found that It is directly proportional to the area of layers in contact. i.e.F∝A…(i) i.e.F∝A…(i) It is directly proportional to the velocity gradient between the layers FF∝Advdx where the constant of proportionality'η' is known as the coefficient of viscosity of a liquid. Hence, coefficient of viscosity of a liquid is defined as the viscus drag or viscus force acting per unit area of the layer having unit velocity gradient perpendicular to the direction of the flow of the liquid .