Fluid Mechanics
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Questions and Answers

What is the buoyancy force exerted on a body when it is partially or wholly immersed in a fluid?

  • equal to the density of the fluid multiplied by the volume of the body
  • equal to the pressure at the surface of the body multiplied by its area
  • equal to the weight of the fluid displaced by the body (correct)
  • equal to the volume of the fluid displaced by the body multiplied by its density

    • What happens to the density of a body when it is heated and its volume increases?

  • density becomes zero
  • density decreases (correct)
  • density increases
  • density remains constant

    • What is the relationship between the volume and density of a body when it is subjected to an increase in pressure?

  • density decreases and volume increases
  • density increases and volume decreases (correct)
  • density remains constant and volume remains constant
  • density increases and volume increases

    • What is the characteristic of a fluid that allows it to take the shape of its container?

    <p>It has no fixed shape</p> Signup and view all the answers

    What is the apparent weight of a body when it is partially or wholly immersed in a fluid?

    <p>less than its actual weight</p> Signup and view all the answers

    What is the force exerted by a liquid at rest on a given surface in contact with it?

    <p>Thrust</p> Signup and view all the answers

    What is the condition for a body to float in a fluid?

    <p>the density of the body is less than the density of the fluid</p> Signup and view all the answers

    What is the condition necessary for a fluid to be in motion?

    <p>External force</p> Signup and view all the answers

    What is the factor that does not affect the hydrostatic pressure of a liquid?

    <p>Amount of liquid</p> Signup and view all the answers

    What is the branch of physics that deals with the study of fluids in motion?

    <p>Hydrodynamics</p> Signup and view all the answers

    What is the term used to describe the net upward force experienced by a body when it is partially or fully submerged in a fluid?

    <p>Upthrust</p> Signup and view all the answers

    What is the factor that affects the upthrust on a body submerged in a fluid, regardless of the body's mass, size, and density?

    <p>Volume of the body inside the fluid</p> Signup and view all the answers

    Why is the upthrust on a fully submerged body more in sea water than in fresh water?

    <p>Because sea water is more dense than fresh water</p> Signup and view all the answers

    What is the result of the weight of a body being equal to the weight of the fluid it displaces?

    <p>The body will float</p> Signup and view all the answers

    What is the term used to describe the ratio of the density of a substance to the density of water?

    <p>Specific gravity</p> Signup and view all the answers

    What is the consequence of the metacentre falling below the centre of gravity in a floating body?

    <p>The body will topple and potentially capsize</p> Signup and view all the answers

    What is the characteristic of laminar flow in a liquid?

    <p>The liquid particles move in the form of layers of different velocities that do not mix with each other</p> Signup and view all the answers

    What is the condition for a body to float in a fluid, in terms of its density and volume?

    <p>The fraction of the volume of the body outside the fluid is equal to the ratio of the densities of the body and fluid</p> Signup and view all the answers

    What is the effect of the crowding of streamlines in a fluid?

    <p>The velocity of the fluid particles increases</p> Signup and view all the answers

    What is the relationship between the weight of a body and the upthrust when it is floating in a fluid?

    <p>The weight of the body is equal to the upthrust</p> Signup and view all the answers

    What is the direction of the buoyancy force acting on a body submerged in a fluid?

    <p>Vertically upwards</p> Signup and view all the answers

    What is the factor that determines the magnitude of the upthrust on a fully submerged body in a fluid?

    <p>The density of the fluid</p> Signup and view all the answers

    Under what condition is the weight of a body equal to the weight of the fluid it displaces?

    <p>When the body is floating</p> Signup and view all the answers

    What is the term used to describe the centre of gravity of the displaced fluid?

    <p>Centre of buoyancy</p> Signup and view all the answers

    Why is the upthrust on a body in sea water more than in fresh water?

    <p>Because sea water is denser than fresh water</p> Signup and view all the answers

    What is the condition for a body to be in neutral equilibrium when it is fully submerged in a liquid?

    <p>The weight of the body is equal to the weight of the liquid it displaces</p> Signup and view all the answers

    What is the effect of a change in the gravitational acceleration on the equilibrium of a floating body?

    <p>The equilibrium of the floating body is not affected by the change in gravitational acceleration</p> Signup and view all the answers

    What is the direction of the couple that acts on a floating body when it is slightly tilted from its equilibrium position?

    <p>The couple acts in the opposite direction of the tilt</p> Signup and view all the answers

    What is the condition for a floating body to be in rotational equilibrium?

    <p>The meta-centre is above the centre of gravity</p> Signup and view all the answers

    What is the relationship between the weight of a body and the upthrust force when the body is fully submerged in a liquid?

    <p>The weight of the body is equal to the upthrust force</p> Signup and view all the answers

    Study Notes

    Fluid Mechanics

    • A fluid is a substance that begins to flow when an external force is applied to it.
    • Liquids and gases are fluids.
    • Fluids do not have their own shape but take the shape of the containing vessel.
    • The branch of physics that deals with the study of fluids at rest is called hydrostatics, and the branch that deals with the study of fluids in motion is called hydrodynamics.

    Hydrostatic Pressure

    • Hydrostatic pressure depends on the depth of the point below the surface (h), nature of the liquid (ρ), and acceleration due to gravity (g).
    • Hydrostatic pressure is independent of the amount of liquid, shape of the container, or cross-sectional area considered.
    • The normal force exerted by a liquid at rest on a given surface in contact with it is called the thrust of the liquid on that surface.

    Floatation

    • When a body floats, the weight of the body = upthrust.
    • The fraction of volume outside the liquid (fout) = Vout / Vin = 1 - ρ / σ.
    • For floatation, ρ = σ(Vout / Vin) = σ(1 - ρ / σ).
    • If the density of the body is greater than that of the liquid, the body will sink.
    • If the density of the body is lesser than that of the liquid, the body will float fully submerged in neutral equilibrium with its top surface in the liquid.

    Archimedes' Principle

    • Archimedes' principle states that when a body is immersed partly or wholly in a fluid, it is buoyed up with a force equal to the weight of the fluid displaced by the body.
    • The force exerted by the fluid is perpendicular to the surface and is equal to the pressure at that point multiplied by the area.
    • The resultant of all these constant forces is called upthrust or buoyancy.
    • Upthrust is independent of all factors of the body such as its mass, size, density, etc., except the volume of the body inside the fluid.
    • Upthrust depends on the nature of the displaced fluid.

    Laminar Flow

    • Laminar flow is a type of fluid flow where the liquid flows over a horizontal surface with a steady flow and moves in the form of layers of different velocities that do not mix with each other.
    • The velocity of liquid flow is always less than the critical velocity of the liquid.
    • Laminar flow is generally used synonymously with streamlined flow.

    Rotatory Equilibrium

    • When a floating body is slightly tilted from its equilibrium position, the centre of buoyancy shifts.
    • The vertical line passing through the new centre of buoyancy and the initial vertical line meet at a point called the meta-centre.
    • For rotational equilibrium of a floating body, the meta-centre must always be higher than the centre of gravity of the body.

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