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Physical Quantities And Measurement Techniques

边玩边学

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课程笔记

Measurement of Length

  • Rulers measure small distances (cm) to the nearest millimetre.
  • Tape measures measure lengths of tens of centimetres.
  • Trundle wheels measure lengths of tens of metres.
  • For small objects, measure multiple (e.g., 4 ball-bearings) and divide by the number to find one dimension.

Trundle wheel

Trundle wheel

Measurement of Volume

  • Measuring cylinders measure the volume of liquids directly.
  • The volume of an irregular solid is found by the displacement method: measure the change in liquid volume.
  • Read the bottom of the meniscus at eye level for accuracy.

Measuring cylinders showing before and after readings

Measuring cylinders showing before and after readings

Measurement of Time

  • Stop-clocks and stopwatches measure time intervals.
  • Human reaction time (≈0.25 s) can cause significant error for short intervals.
  • To reduce uncertainty, measure the time for multiple oscillations (e.g., 10 swings) and divide by the number.
  • Use a fiducial marker (e.g., a line at equilibrium) to improve timing accuracy.

Two stopwatches showing the start and end of a lap

Two stopwatches showing the start and end of a lap

Multiple Readings & Accuracy

  • Taking multiple readings reduces the impact of random errors.
  • Example: measure thickness of 100 sheets of paper, then divide by 100 for average thickness of one sheet.
  • Two measurements are considered equal within experimental accuracy if they differ by less than 10%.

Taking multiple readings to improve accuracy

Taking multiple readings to improve accuracy

Scalars & Vectors

  • Scalar quantities have magnitude only (e.g., mass, distance, speed, energy).
  • Vector quantities have both magnitude and direction (e.g., weight, displacement, velocity, force).
  • Distance is the total path length (scalar); displacement is the straight‑line distance from start to finish (vector).
  • Speed is distance per unit time (scalar); velocity is displacement per unit time (vector).
  • An object can have constant speed but changing velocity if it changes direction.

Distance vs displacement

Distance vs displacement

Examples of Scalars & Vectors

  • Scalars: distance, speed, mass, energy, volume, density, temperature, power.
  • Vectors: displacement, velocity, weight, force, acceleration, momentum.
  • Mass is a scalar; weight is a vector (force due to gravity).
  • Mass does not change with location; weight depends on gravitational field strength.

Examples of scalar and vector quantities

Examples of scalar and vector quantitiesScalarVectordistancedisplacementspeedvelocitymassweight

幻灯片

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练习题

免费预览——34 题中的 8 题。注册即可查看全部。
  1. 1.The diagram shows four identical ball-bearings placed between two blocks on a steel ruler. The total length of the four ball-bearings is 8 cm. Calculate the diameter of one ball-bearing in cm.

    Easy
    • A1
    • B2
    • C3
    • D4
  2. 2.A stopwatch reads 0:55:10 at the start of a lap and 1:45:10 at the end. Calculate the time taken for the lap in seconds.

    Easy
    • A45
    • B55
    • C50
    • D60
  3. 3.State the typical human reaction time for an alert person.

    Easy
  4. 4.What is a scalar quantity?

    Easy
  5. 5.What is a vector quantity?

    Easy
  6. 6.Distance is a scalar quantity.

    Easy

    True or false?

  7. 7.Displacement is a scalar quantity.

    Easy

    True or false?

  8. 8.Match each quantity to its type (scalar or vector).

    Easy
    • distance
    • displacement
    • speed
    • velocity
    • scalar
    • vector
    • scalar
    • vector

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