Uncertainty in Measurements Density How do you make

Uncertainty in Measurements & Density

How do you make a measurement? Ø Estimate one more digit than you can read. Ø The estimated digit is called the uncertainty in the measurement!

Example: Answer: 3. 51 cm or 35. 1 mm Example: Answer: 279. 1 g Which digit is uncertainty in the measurement? Answer: The 1

Problem 1 Problem 2 Answer: 11. 80 cm Answer: 8. 79 m. L Problem 3 Answer: 11. 51 m. L

Density is a relationship • Density is the relationship between mass (m) and volume (V) Density = Mass/Volume D = m/V

Mass and Volume • Volume (V) – Volume is the amount of space something takes up – The units of volume are usually cm 3 or m. L • Mass (m) – Mass is how much of something you have – The units of mass are usually grams (g)

Example: • Find the density of a block with a Mass of 2. 750 g Vol= length x width x height V=(3. 10 cm)(3. 30 cm) V = 31. 71 cm 3 D = 2. 750 g/31. 71 cm 3 D = 0. 0867 g/cm 3 3. 10 cm 3. 30 cm 3. 10 cm

Percent Error % Error = A. V. - Ex. V. x 100 A. V. = Actual Value (given) = 0. 0900 g/cm 3 Ex. V. = Experimental Value (your value) = 0. 0867 g/cm 3 % Error = 0. 0900 - 0. 0867 x 100 = 3. 7% 0. 0900

Lastly! • Percent error < 7% means that you were accurate. • Your goal is to be under 7% error in lab tomorrow, otherwise, you must re-do calculations and/or measurements! • Good Luck!!