Chapter 11

• What is the definition of density?

  Mass per unit volume
• What is the unit of density?

  Kilogram per cubic metre (kg/m³)
• How can you measure the density of an object?

  By measuring mass and volume
• How does the density of lead compare to aluminium?

  Lead is much more dense than aluminium
• How can you determine how much denser one substance is than another?

  By measuring the mass of equal volumes
• What is the formula for calculating density?

  Density = mass/volume
• What is the rearranged formula for mass?

  m = ρV
• What is the rearranged formula for volume?

  V = m/ρ
• Why are gases less dense than solids or liquids?

  Because molecules in gases are more separated
• What are the procedures to measure the density of different substances?

  1. Regular solid:

  • Measure mass
  • Measure dimensions and calculate volume
  • Calculate density from mass/volume

  1. Liquid:

  • Measure mass of empty cylinder
  • Measure volume of liquid
  • Calculate mass of liquid and density

  1. Irregular solid:

  • Measure mass
  • Immerse in liquid to find volume
  • Calculate density from mass/volume
• What is an alloy?

  A solid mixture of two or more metals
• What is brass an alloy of?

  Copper and zinc
• How is the volume of metal A in an alloy calculated?

  VA = fA x V
• How is the mass of the alloy calculated?

  m = ρA VA + ρB VB
• How do you calculate the density of an alloy?

  ρ = m/V
• What are the densities of some common substances?

  • Air: 1.2 kg/m³
  • Aluminium: 2700 kg/m³
  • Copper: 8900 kg/m³
  • Gold: 19,300 kg/m³
  • Hydrogen: 0.083 kg/m³
  • Iron: 7900 kg/m³
  • Lead: 11,300 kg/m³
  • Oxygen: 1.332 kg/m³
  • Silver: 10,500 kg/m³
  • Water: 1000 kg/m³
• How do you calculate the density of a rectangular brick with mass 2 kg and dimensions 20 cm × 10 cm × 5 cm?

  Density = 2 kg / 0.01 m³
• What is the density of a metal cube with a mass of 7 kg and a hole of volume 0.02 m³?

  Depends on remaining mass and volume
• What is the energy stored in a stretched spring?

  Elastic potential energy
• What is Hooke's law?

  Force is directly proportional to extension
• What is the formula for Hooke's law?

  F = kΔL
• What is the unit of the spring constant?

  it is dimensionless
• What happens if a spring is stretched beyond its elastic limit?

  It does not return to its initial length
• How do you calculate the spring constant from a given force and extension?

  k = F/ΔL
• What is the extension of a spring with a tension of 20 N and spring constant of 25 N m⁻¹?

  0.8 m
• What is the tension in a spring extended by 0.50 m with a spring constant of 25 N m⁻¹?

  12.5 N
• What are the characteristics of materials under tension?

  • Steel spring: Follows Hooke's law, linear relationship
  • Rubber band: Initially extends easily, then becomes difficult
  • Polythene strip: Initially gives, then becomes difficult to stretch
• What is tensile stress?

  Force per unit area
• What is the unit of tensile stress?

  Pascal (Pa)
• What is tensile strain?

  Extension divided by original length
• What is the unit of tensile strain?

  No units
• What is Young's modulus?

  • A measure of the stiffness of a material
  • Defined as stress/strain
  • Different materials have different Young's moduli
• What are the shapes of stress-strain graphs for different materials?

  • Steel: Linear up to yield point
  • Rubber: Non-linear, large deformation
  • Polythene: Initial linear, then non-linear
• How do you measure the extension of a material under tension?

  Using apparatus like Searle's apparatus
• What is the elastic limit?

  The maximum stress a material can withstand
• What happens to a material when it exceeds its elastic limit?

  It undergoes permanent deformation
• What is the relationship between force and extension in a spring?

  Directly proportional until elastic limit
• How do you calculate the energy stored in a stretched spring?

  Using Eₚ = (1/2)FΔL
• What is the formula for elastic potential energy in terms of spring constant?

  Eₚ = (1/2)kΔL²
• What is the gravitational acceleration constant?

  9.8 m/s²