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Physics Chapter 6 : Topic 9
Viscous Drag Force
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When an object moves through a fluid, the fluid exerts a force that opposes its motion. This force is called:
Reasoning: Viscous drag is the resistance offered by fluid against the motion of an object.
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The direction of viscous force on a moving object is:
Reasoning: Viscosity produces a retarding force that opposes relative motion.
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A falling object in air experiences resistance because:
Reasoning: Air has viscosity and exerts drag on moving objects.
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The retarding force due to viscosity depends mainly on:
Reasoning: Viscous force arises due to relative movement between fluid layers and object.
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A body moving slowly through a highly viscous liquid experiences:
Reasoning: Higher viscosity produces greater resistance.
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Viscous drag occurs because:
Reasoning: Molecular interactions between fluid layers create resistance.
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When an object moves through a fluid, it causes nearby fluid layers to:
Reasoning: The moving object transfers momentum to nearby fluid layers.
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The interaction responsible for viscous drag is:
Reasoning: Internal friction between fluid molecules produces viscosity.
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A fluid resists the motion of an object because:
Reasoning: Viscosity acts against relative movement.
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If viscosity of a fluid increases, the drag force on an object:
Reasoning: More viscous fluids provide greater resistance.
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According to Stokes’ law, viscous force on a small sphere is:
Reasoning: Stokes’ law gives viscous drag on a sphere moving through a fluid.
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According to Stokes’ law, viscous force depends directly on:
Reasoning: $\mathbf{F = 6\pi\eta rv}$ $\mathbf{\Longrightarrow}$ Force increases with radius.
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If the velocity of an object moving through a viscous fluid doubles, the viscous force:
Reasoning: Stokes’ law shows viscous force is directly proportional to velocity.
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A larger sphere moving through the same liquid experiences:
Reasoning: Larger radius increases viscous force.
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The viscous drag on a sphere increases when:
Reasoning: Drag is proportional to velocity.
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Terminal velocity occurs when:
Reasoning: At terminal velocity, net force becomes zero.
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A falling object reaches terminal velocity because:
Reasoning: Increasing velocity increases viscous drag.
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At terminal velocity, the acceleration of an object is:
Reasoning: Forces are balanced, so net force is zero.
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A raindrop does not continue accelerating forever because:
Reasoning: Air drag eventually balances gravitational force.
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When viscous drag equals weight of a falling object:
Reasoning: Balanced forces produce constant velocity.
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A small sphere falls through oil. If viscosity of oil increases, terminal velocity:
Reasoning: Greater viscosity produces more drag and reduces terminal velocity.
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Two identical balls fall through water and oil. The ball reaches terminal velocity faster in:
Reasoning: Oil has higher viscosity and produces stronger drag.
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A parachute slows a falling person because it:
Reasoning: Larger area increases air resistance.
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A streamlined object experiences less drag because:
Reasoning: Streamlining reduces resistance from the fluid.
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A swimmer moves slower in honey than water because honey has:
Reasoning: Higher viscosity produces greater drag.
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Which factor does NOT significantly affect viscous drag?
Reasoning: Colour has no effect on viscous resistance.
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A moving object slows down in a fluid after the applied force is removed because:
Reasoning: Drag acts opposite to motion.
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The retarding force due to viscosity converts mechanical energy mainly into:
Reasoning: Friction between molecules produces heat.
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In vacuum, a falling object experiences:
Reasoning: Vacuum contains no fluid to produce resistance.
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An object moving faster through the same fluid experiences:
Reasoning: Viscous force increases with velocity.
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If radius of a sphere is doubled while velocity and viscosity remain constant, viscous force becomes:
Reasoning: $\mathbf{F = 6\pi\eta rv}$ $\mathbf{\Longrightarrow}$ Force is directly proportional to radius.
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If velocity of a sphere becomes three times, viscous drag becomes:
Reasoning: Drag is directly proportional to velocity.
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A small sphere falling in a viscous liquid reaches terminal velocity when:
Reasoning: Balanced forces result in terminal velocity.
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A car moving through air experiences resistance mainly because:
Reasoning: Air resistance is a form of viscous drag.
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Increasing the surface area of a parachute increases drag because:
Reasoning: Larger area increases resistance from air.
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The main reason viscous force acts as a retarding force is that it:
Reasoning: Viscous force opposes relative movement between object and fluid.
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