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1.6.1: Measurements, Quantities, and Unity Factors Lecture Demonstrations

  • Page ID
    49939
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    Convert Mass

    Convert 12 lb weight of bowling ball to g, showing unity factors

    12.00 lb x 453.59237 g/lb = 5443 g

    Calculate and convert volumes

    V=4/3 π r3

    V = 4/3 * 3.1416 * (1/2 * 8.59 in)3 =

    4/3 * 3.1416 * 79.23 in3

    =331.9 in3

    Unity Factor: 2.54 cm = 1 in

    331.9 in3 x (2.54 cm / 1 in)3 Note!!!

    331.9 in3 x 16.39cm3/in3

    = 5439 cm3

    Densities

    Will the bowling ball float in water? Demo [1]

    D = 5443 g / 5439 cm3 Too close to call. See Errors in Measurement Lecture Demonstrations

    Mass vs. Weight

    What is the mass of hydrogen?

    Density of hydrogen at room temperature and 1 Atm = 0.082 g/L

    What is the volume in L, assuming same size as bowling ball? Unity Factors?

    1 cm3 = 1 mL = 10-3L (Note: 1 mL = 1 cm3 = “1 cc”)

    V (L) = 5500 cm3 x (1 L / 1000 cm3)

    m (g) = V (L) * D (g/L) = 5.500 L x 0.082 g/cm3

    = 0.451 g

    Why does the Hydrogen balloon float? F = W = m g

    F = W = (0.451 g x 1 kg /1000g) * 9.8 m*s-2 =

    = 0. 0044 N

    Force Upward: (Archimedes)

    D of air = 1.2 g /L; Archimedes Principle: buoyancy = mass of air displaced (6.6 g)

    F = m g

    F = ( 6.6 g x 1 kg /1000g) * 9.8 m*s-2 =

    = 0. 065 N

    Net force = 0.065 N - 0.044 N upwards.

    References

    1. J. Chem. Educ., 2004, 81 (9), p 1309

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