BIOD43H3 Lecture Notes - Lecture 9: Parasitic Drag, Viscosity, Flow Separation
Lecture 9- Movement in Fluid (Water Part 1)
Locomotion in the Fluid Water
• Humans are always surrounded by the medium of air and walk through it with little
force. Similarly, fish are always surrounded by the medium of water, however water is
much more viscous than air, so fish must use their body appendages to push back with
equal force (GRF).
• Fish use THRUST to push against water particles with moment.
THRUST= is determined by the rate that animal transfers momentum. Fish can increase
thrust
by beating tail more rapidly
Animals always lose momentum to their surrounding fluid
• DRAG= A force that acts against direction of animal movement.
-Pressure drag is the pressure fluid that exerts on aial’s skin as it deforms around
animal
-Friction drag is the resistance of fluid to shear
• Inertia explains the tendency of an object to resist a change in its state of motion or
rest. Example, an object moving steadily will continue to move unless acted against by
an outside force
• Resistive forces depend on the viscosity (thickness) of the fluid, and the pressure the
fluid exerts on the object. The thicker the medium the greater the resistive force.
• Only fluids can be measured as viscous (NOT solids)
• Fluids move in response to applied force
• Shear stress= The force vector parallel to material cross section
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Document Summary
Lecture 9- movement in fluid (water part 1) Locomotion in the fluid water: humans are always surrounded by the medium of air and walk through it with little force. Thrust= is determined by the rate that animal transfers momentum. Fish can increase thrust by beating tail more rapidly. Animals always lose momentum to their surrounding fluid: drag= a force that acts against direction of animal movement. Pressure drag is the pressure fluid that exerts on a(cid:374)i(cid:373)al"s skin as it deforms around animal. Friction drag is the resistance of fluid to shear. Inertia explains the tendency of an object to resist a change in its state of motion or rest. Example, an object moving steadily will continue to move unless acted against by an outside force: resistive forces depend on the viscosity (thickness) of the fluid, and the pressure the fluid exerts on the object.
