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Physics 9
| Question | Answer |
|---|---|
| What is density | Density is mass per unit volume. ρ = m/V, where ρ is in kg/m³. Note: 1 g/cm³ = 1000 kg/m³. |
| How do you express weight in terms of density? | W = ρVg, combining W = mg with ρ = m/V. |
| What is buoyant force and what causes it? | An upward force on a submerged object caused by the pressure difference between the bottom and top of the object. |
| What is Archimedes' Principle? | When an object is partially or completely immersed in a fluid, the buoyant force equals the weight of the fluid displaced. |
| For a completely submerged object, what is the relationship between displaced volume and object volume? | V_submerged = V_displaced = V_object (all three are equal). |
| What is specific gravity and how is it calculated? | The ratio of an object's density to the density of water at 4°C (1000 kg/m³). SG = ρ_obj / ρ_H₂O. SG < 1 → floats; SG > 1 → sinks. |
| What is pressure and what is its formula? | The concentration of force applied over an area. P = F/A, measured in pascals (Pa). |
| What is hydrostatic pressure and its formula? | The pressure exerted by a fluid at rest due to the weight of fluid above. P = ρgh, where h is the depth. Deeper depth and higher fluid density both increase hydrostatic pressure. Size of the submerged object does not matter. |
| When must atmospheric pressure be added to hydrostatic pressure? | When any part of the fluid is exposed to the atmosphere. The atmospheric pressure distributes throughout the fluid and must be included. |
| What is gauge pressure? | The pressure of a system relative to atmospheric pressure — how much above or below atmospheric pressure a fluid is. Can be positive or negative. |
| What is absolute pressure and its formula? | The total pressure of a system including atmospheric pressure. P_abs = P_atm + P_gauge. Standard atmospheric pressure = 1 atm = 101.3 kPa = 1.013 × 10⁵ Pa. |
| What is Pascal's Principle? | Pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid. |
| What is the hydraulic system equation derived from Pascal's Principle? | P₁ = P₂, therefore F₁/A₁ = F₂/A₂. A small force on a small piston creates a proportionally larger force on a larger piston. |
| What is stress and its formula? | The ratio of a perpendicular applied force to the cross-sectional area of an object. σ = F⊥/A, measured in Pa or N/m². |
| What is strain and its formula? | The fractional deformation of a material when stress is applied. ε = Δl/l₀. It is dimensionless. |
| What is Young's Modulus and its formula? | A measure of a material's stiffness — the ratio of stress to strain within the elastic limit. Y = σ/ε. Higher Y = stiffer material (e.g., steel). Lower Y = more flexible (e.g., rubber). |
| Why does a needle penetrate skin more easily than a finger applying the same force? | Because pressure is inversely related to area (P = F/A). The needle concentrates force over a much smaller area, creating far greater pressure at the point of contact. |
| Why don't we feel atmospheric pressure crushing us? | Because the fluids inside our body push outward with the same force as the atmosphere pushes inward, creating a pressure equilibrium. |
| Why is water at 4°C used as the reference point for specific gravity? | Because water reaches its maximum density of 1000 kg/m³ at 4°C, making it a consistent and standardized reference point for comparing densities. |
| Why does pressure increase with depth in a fluid but not depend on the size of the submerged object? | Pressure depends only on the weight of fluid directly above a point (P = ρgh). The size or shape of a submerged object doesn't change how much fluid is above any given depth, so all objects at the same depth experience the same pressure. |
| What is the difference between gauge pressure and absolute pressure in a practical context, and why does it matter? | Gauge pressure measures pressure relative to the atmosphere, while absolute pressure includes atmospheric pressure as well. Blood pressure is gauge pressure. If it were absolute, it would be below atmospheric pressure, which causing blood vessel collapse. |
| What is the density of water? | 1,000 kg/m³ or 1 g/cm³ |
Created by:
smurtab