What is density?
The mass per unit volume of a substance. \( \text{Density} = \frac{\text{Mass}}{\text{Volume}} \)
What is the SI unit of density?
kg/m³
What is relative density?
The ratio of the density of a substance to the density of water.
Give the formula for relative density using mass.
\( R.D = \frac{\text{Mass of substance}}{\text{Mass of equal volume of water}} \)
Give the formula for relative density using density.
\( R.D = \frac{\text{Density of substance}}{\text{Density of water}} \)
State Archimedes' Principle.
A body immersed in a fluid experiences an upthrust equal to the weight of the fluid displaced.
What is upthrust?
The upward force exerted by a fluid on a submerged object.
How is upthrust calculated using weights?
\( U = W_A - W_F \), where \( W_A \) is the weight in air and \( W_F \) is the weight in fluid.
Give the formula for upthrust using fluid properties.
\( U = \rho \cdot V \cdot g \)
What is the principle of floatation?
A floating body displaces a weight of fluid equal to its own weight.
Why do ships float?
They displace water equal in weight to their own, balancing upthrust and weight.
State the formula for floatation equilibrium.
\( W_{\text{body}} = W_{\text{fluid displaced}} \)
What is surface tension?
The force per unit length acting on the surface of a liquid at right angles to a line in the surface.
State the formula for surface tension.
\( r = \frac{F}{2L} \)
Give the SI unit of surface tension.
Newton per meter (N·m⁻¹)
List two effects of surface tension.
Water forms spherical droplets; a needle floats on water when placed gently.
Name two factors that reduce surface tension.
Heating and adding soap or detergent.
What is capillarity?
The ability of a liquid to rise or fall in a narrow tube due to adhesive and cohesive forces.
State two uses of capillarity.
Ink rising in blotting paper; water rising in plant stems.
What is cohesion?
Attraction between molecules of the same kind, e.g. mercury molecules.
What is adhesion?
Attraction between molecules of different substances, e.g. water and glass.
Why does water rise in a capillary tube?
Adhesive forces between water and glass are stronger than cohesive forces in water.
Why does mercury fall in a capillary tube?
Cohesive forces in mercury are stronger than adhesive forces with glass.
What is the upthrust when an object floats?
Equal to the object's weight.
What happens if an object's weight is greater than upthrust?
The object sinks.
List two examples of fluids.
Liquids and gases.
Why are liquids and gases called fluids?
They can flow and take the shape of their container.
State one application of surface tension.
Used in waterproof materials like umbrellas.
What is the role of capillarity in plants?
Helps in the upward movement of water from roots to leaves.
What is the equation for relative density using upthrust?
\( R.D = \frac{\text{Weight in air}}{\text{Upthrust in water}} \)
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