1.6.1: Measurements, Quantities, and Unity Factors Lecture Demonstrations
- Page ID
- 49939
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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
- J. Chem. Educ., 2004, 81 (9), p 1309