Question

Fluid friction depends on __________
(A). Speed of the object
(B). Shape of the object
(C). Nature of the object
(D). All of the above

Answer 1

Hint: Fluid friction is also called viscosity. It resists relative motion between different layers of a liquid or opposes the motion of a body on the surface of a liquid or inside it. The greater the extent and tendency of the relative motion, the greater is the fluid friction. Naturally, the speed of the object and its shape play a part in fluid friction along with the nature of the fluid.

Complete step by step answer:

Fluid friction or viscosity is an inherent property of fluids much like the force of friction between two rough surfaces. Fluid friction also dissipates kinetic energy and resists relative motion between different layers of a liquid and the motion of a body on or inside a liquid.
When an object moves inside or on a liquid it tries to pull the layer of the liquid surrounding it along with itself. This causes a relative motion between that layer and the other layers of the liquid. The fluid friction opposes this motion and hence slows the object down.
If the object moves with high speed, there is a higher tendency of relative motion between the fluid layers and hence, the fluid exerts a greater frictional force.

If the area of the object (depends on its shape) is large, it tries to pull a larger layer of liquid along with itself which causes a greater tendency of relative motion and hence greater fluid friction.

Fluid friction also depends on the nature of the liquid. Some fluids (like honey) have a greater coefficient of viscosity (apply more fluid friction) than less viscous fluids (like water) having a smaller coefficient of viscosity under the same conditions.
Hence, fluid friction depends on all three, the speed and shape of the object and the nature of the fluid.
Hence, the correct option is D) All of the above.

Note: Students may have heard in mechanics that friction does not depend on the area of contact and thus may think that the shape of the object has nothing to do also with fluid friction. However, this is wrong as explained above since friction between two surfaces and friction in a fluid arise due to different reasons. However, it should also be said that some very recent research has shown that friction between two surfaces may also depend on the speed of the object and the area of contact (shape of the object) like fluid friction.
A good experiment to get a feel for fluid friction at home is to try and stir a spoon in a glass of water and a jar of honey. It takes a lot more effort to stir the spoon in the jar of honey, since honey is much more viscous and applies greater fluid friction.