Properties of Bulk Matter

Elastic Behaviour

Meaning: Elasticity is the ability of a material to return to its original shape and size after the external force (load) is removed.

Simple Explanation: Imagine a spring. You pull it (it stretches), you let it go (it snaps back). That "snapping back" is elastic behaviour. If a material does not return to its original shape (like chewing gum), it is called plastic.

• Elastic Limit: The maximum extent to which a body can be deformed and still return to its original shape.
• Permanent Set: If you stretch something beyond its elastic limit, it stays deformed.

Examples

• A steel wire used in a guitar string.
• A rubber band used to tie a bundle of pencils.

Real-Life Use: Bridge Construction

Engineers use steel for bridges because it has high elasticity. When heavy trucks drive over a bridge, the steel beams bend slightly under the weight (stress) but return to their original position once the truck passes.

Stress and Strain Relationship

Stress: The internal restoring force acting per unit area.
Formula: $\text{Stress} = \frac{\text{Force}}{\text{Area}}$ (Unit: $\text{N/m}^2$ or Pascal)

Strain: The fractional change in the dimensions of the body. It has no unit because it is a ratio.
Formula: $\text{Strain} = \frac{\text{Change in Dimension}}{\text{Original Dimension}}$

Hooke's Law: For small deformations, Stress is directly proportional to Strain.
$\text{Stress} = E \times \text{Strain}$ (where $E$ is the Modulus of Elasticity).

Moduli of Elasticity

• Young's Modulus ($Y$): Deals with length (stretching/compressing).
  $\text{Young's Modulus} = \frac{\text{Longitudinal Stress}}{\text{Longitudinal Strain}}$
• Bulk Modulus ($B$): Deals with volume (compressing from all sides).
  $\text{Bulk Modulus} = \frac{\text{Volume Stress}}{\text{Volume Strain}}$
• Shear Modulus ($G$): Deals with shape (sliding layers).
  $\text{Shear Modulus} = \frac{\text{Shearing Stress}}{\text{Shearing Strain}}$

Pressure and Pascal's Law

Pressure: The perpendicular force exerted by a fluid per unit area.
$\text{Pressure} (P) = \frac{\text{Force}}{\text{Area}}$

Pascal's Law: Any pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.

Real-Life Use: Hydraulic Brakes
When you press the brake pedal, pressure is transmitted through the brake fluid to larger pistons at the wheels, applying a massive force to stop the car.

Buoyancy and Archimedes' Principle

Buoyancy: The upward force exerted by a fluid on an object immersed in it.

Archimedes' Principle: When a body is immersed fully or partially in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced by it.

Real-Life Use: Submarines
Submarines use "ballast tanks." They fill them with water to dive (increasing weight) and pump compressed air in to surface (decreasing weight).

Fluid Flow & Viscosity

• Streamline Flow: Smooth, orderly flow where every particle follows the same path.
• Turbulent Flow: Chaotic flow with swirls and eddies.
• Bernoulli's Theorem: $P + \frac{1}{2}\rho v^2 + \rho gh = \text{constant}$
• Viscosity: The "internal friction" of a fluid (e.g., Honey is more viscous than water).
• Stokes' Law: $F = 6\pi\eta rv$

Surface Tension and Capillarity

Surface Tension: The property of a liquid surface to behave like a stretched elastic membrane.

Capillarity: The rise or fall of a liquid in a very narrow tube. Example: Water traveling from roots to leaves in plants.

Heat and Temperature

• Temperature: A measure of the average kinetic energy of molecules.
• Heat: The energy transferred from a hotter body to a colder body.

Thermal Expansion

Most substances expand when heated. This includes Linear, Area, and Volume expansion.

Real-Life Use: Railway Tracks
Small gaps are left between tracks so that during hot summers, the steel can expand without bending.

Specific Heat and Calorimetry

Specific Heat Capacity ($c$): Heat required to raise the temperature of 1 kg of a substance by $1^\circ\text{C}$.
Formula: $Q = mc\Delta T$

Change of State and Latent Heat

Latent Heat: The "hidden" heat absorbed or released during a phase change while temperature remains constant.

• Fusion: Solid $\to$ Liquid
• Vaporization: Liquid $\to$ Gas

Heat Transfer Mechanisms

• Conduction: Transfer through direct contact (Metal rod).
• Convection: Transfer through movement of fluids (Boiling water).
• Radiation: Transfer via EM waves; no medium needed (Sun's heat).

Formula Summary

Solids vs. Fluids

Methods of Heat Transfer

• Materials Science: "Shape Memory Alloys" (Nitinol) used in medical stents.
• Aerospace: Bernoulli's principle is the basis for airfoil design (plane wings).
• Civil Engineering: "Expansion Joints" in bridges prevent failure due to thermal expansion.
• Nanotechnology: Super-hydrophobic coatings created via surface tension studies.

1. Which of the following is the most elastic material?
   Answer: b) Steel
2. The unit of stress is the same as that of:
   Answer: c) Pressure
3. According to Pascal's Law, pressure in a confined fluid is:
   Answer: c) Transmitted equally in all directions
4. A ship floats on water because of:
   Answer: c) Buoyant force
5. The speed of a falling raindrop becomes constant due to:
   Answer: c) Viscosity
6. Which effect allows insects to walk on water?
   Answer: b) Surface Tension
7. Water rises in a thin glass tube because of:
   Answer: b) Capillarity
8. The process of heat transfer that does not require a medium is:
   Answer: c) Radiation
9. The heat required to change a solid to a liquid at constant temperature is:
   Answer: b) Latent heat of fusion
10. If the temperature of a metal rod increases, its length typically:
    Answer: b) Increases

1. Q: Distinguish between Elasticity and Plasticity.
   Ans: Elasticity is the property to regain original shape after removing force (e.g., Steel). Plasticity is when a body remains deformed (e.g., Putty).
2. Q: State Hooke's Law and give its mathematical expression.
   Ans: Within the elastic limit, stress is directly proportional to strain: $\text{Stress} = E \times \text{Strain}$.
3. Q: Why does a needle float on water if placed carefully, but sink if pushed?
   Ans: It floats due to surface tension. Once pushed, the "skin" breaks, and the high density of steel causes it to sink.
4. Q: Explain the difference between Streamline and Turbulent flow.
   Ans: Streamline is smooth and constant; Turbulent is irregular with eddies and vortices.
5. Q: What is Bernoulli's Theorem? Give one application.
   Ans: Sum of pressure, kinetic, and potential energy per unit volume is constant. Application: Airplane wing lift.
6. Q: Define Viscosity. How does it change with temperature for liquids?
   Ans: Internal resistance to flow. For liquids, viscosity decreases as temperature increases.
7. Q: What is the difference between Heat and Temperature?
   Ans: Heat is energy in transit; Temperature is the measure of average kinetic energy.
8. Q: Explain "Latent Heat" and why temperature doesn't rise during a phase change.
   Ans: Heat used to break intermolecular bonds instead of increasing kinetic energy.
9. Q: State Newton's Law of Cooling.
   Ans: Rate of heat loss is proportional to the temperature difference between the body and surroundings.
10. Q: Why is water used as a coolant in car radiators?
    Ans: It has a very high specific heat capacity, absorbing large amounts of heat without a huge temperature rise.

• The "Moduli" Map: Young $\to$ Yawn (Length), Bulk $\to$ Balloon (Volume), Shear $\to$ Slide (Shape).
• Heat Transfer Trio: Conduction $\to$ Contact, Convection $\to$ Currents, Radiation $\to$ Rays.
• Stress/Strain Logic: Stress is the Struggle (Force), Strain is the Stretch (Change).