Physics Concepts: SI Units and Motion

SI Units

• The SI unit for luminous intensity is the candela (cd).
• Ampere (A), meter (m), and kilogram (kg) are SI units for electric current, length, and mass respectively.
• Derived physical quantities are units derived from the fundamental SI units.
• Speed, volume, and force are examples of derived quantities.
• Mass is a fundamental SI unit, not a derived quantity.

Rounding off to Significant Figures

• When rounding off to 3 significant figures:
  • 2.745 rounds to 2.75
  • 2.735 rounds to 2.74

Velocity-Time Graphs

• The slope of a velocity-time graph represents the acceleration of an object.

Speedometers

• A speedometer measures the instantaneous speed of a vehicle, which is the magnitude of its velocity at a specific moment in time, not the average speed or average velocity.

Vectors

• The angle between two equal vectors is 0°, 60°, or 120°.

Projectile Motion

• Doubling the initial speed of a projectile, while keeping the projection angle constant, quadruples the horizontal range.

Elasticity

• Steel is more elastic than rubber because, under the same deforming force, steel experiences a smaller deformation than rubber.

Stress

• The dimensional formula of stress is $ML^{-1}T^{-2}$.

Pressure in Liquids

• When air is pumped out of a closed jar containing a beaker of liquid, the pressure in the liquid near the bottom of the liquid:
  • Initially decreases due to reduced atmospheric pressure.
  • Then increases, because the liquid vapor pressure starts to contribute more significantly as the air pressure is reduced.

Viscosity

• Honey is more viscous than water.

Thermal Expansion

• The increase in length of a metal bar when heated is greater if:
  • The bar is longer
  • The temperature rise is larger.

Wein's Displacement Law

• Wein's displacement law can be used to determine the temperature of a star based on the wavelength at which it radiates the most energy.

Thermos Flasks

• A thermos flask is polished to reflect all radiation from outside, which helps minimize heat loss through radiation.

Supplementary SI Unit

• Steradian is a supplementary SI unit, used to measure solid angles.

Negative Acceleration

• Negative acceleration signifies a decrease in velocity.

Compressibility

• Per pascal is the SI unit of compressibility.

Viscosity and Temperature

• The viscosity of a gas increases as its temperature increases.

Thermal Conduction

• Solids are heated by the mode of conduction.