Measurement Is Not a Trivial Subject. Attempting to Reach a Desired Precision Is a Subject

Name: ______Date: ______Day: _____@_____

Density

Measurement is not a trivial subject. Attempting to reach a desired precision is a subject of great study. The difference in precision for technology (~10%), engineering (~1%), or science (<1%) is profound. Each has its place and all serve their purpose. This experiment encourages you to make careful measurements so that for the remainder of the semester you know how to take reliable data.

Units are perhaps the most under appreciated part of physics by students. Without units all of physics would be reduced to meaningless numbers. So units carry the meaning of the measurements. Of course without the number, the units serve no purpose. (NB: this lab is worth 25 points.)

Table 1. Qualitative: (1 point)

Object /

Description

1 / Shape: / Color: / Material:
2 / Shape: / Color: / Material:
3 / Shape: / Color: / Material:

Table 2. Quantitative: (3 points)

Object / m (g) / L(cm) / W(cm) / H(cm) / V(cm3) /  (g/cm3) / Ave.  (g/cm3) / %
Rect. Cube
Cylinder 1 / d =
d =
d =
Cylinder 2 / D =
D =
D =

Sample Calculations: (1 point each)

V =

 =

% =

Density (2 of 2)

Answer all questions on this sheet of paper. Place your answer on the blank line at the right.

Question #1: (1 point each) Thecorrect measurements of a cylinder are h = 5.10 cm and d = 3.93 cm.

(a) Calculate the volume of this cylinder.

Va =

(a) ______

(b) You make a –5% measurement error in the height, while d is correct. Calculate the incorrect volume:

Vb =

(b) ______

V% = (Va –Vb)*100/ Va =

(d) You make a –5% error in the diameter, while ‘h’ is correct. Calculate the incorrect volume:

Vd =

(d) ______

(e) Calculate the percent error in volume between the two volumes, Va and Vd:

V% = (Va –Vd)*100/ Va =

(e) ______

Question #2:(2 points) Using algebra only, what percent error in volume do you make when you measure a +5% error in the diameter d of a sphere?

V% =

V% = ______