Lab 3/6
Summary: today I worked on:
1) Finding the density of a squash ball
2) Finding the coefficient of kinetic friction of a squash ball
1) Goal: Find density of squash ball
Procedure: measure mass with scale, volume by placing ball fragment in beaker filled with water,
measuring change in volume
Piece 1 (one half of ball): 80 mL of water, put half of ball in, now it’s about 90 mL. V≈10mL
Mass: 12.03 grams
Volume≈10 mL
Density=M/V=12.03g/10mL=1.203g/mL
Piece 2 (other half with chunk taken out):
Mass: 10.73 grams
Volume≈6 mL
Density=M/V=10.73g/6mL= 1.783g/mL
Piece 3 (the chunk that was taken out of piece 2 half):
Mass: 0.83 grams
Volume≈1 mL
Density=M/V=0.83g/1mL= 0.83g/mL
Mean: 1.27 g/mL; Standard Deviation 0.48 g/mL
Largest source of error: volume estimation (we had a beaker with 20 mL increments)
Solution: use a container with smaller volume increments.
Measuring density round 2:
We found a container with 2.5 mL resolution that we are using to remeasure the volume to get a more
precise density calculation
Split pieces 1 and 2 into 4 pieces (we’ll call them 4,5,6,7)
Piece 4:
Mass: 2.71 grams
Volume= 2.5 mL
Density=M/V=2.71g/2.5mL= 1.08 g/mL
Piece 5:
Mass: 2.68 grams
Volume= 2.4 mL
Density=M/V=2.68g/2.3mL= 1.12 g/mL
Piece 6:
Mass: 2.38 grams
Volume= 2.3 mL
Density=M/V=2.38g/2.3mL= 1.03 g/mL
Piece 7:
Mass: 2.35 grams
Volume= 2.3 mL
Density=M/V=2.35g/mL= 1.02 g/mL
Average of these is 1.0625, standard deviation=0.04
Conclusion: Density of a squash ball is around 1.06 g/mL
2) Goal: Measure coefficient of volumetric thermal expansion of squash ball (∝𝑣 )
We should also consider how porous it is (when placed in water)
Procedure: put it in a beaker of water, put on hot plate, slowly heat up and see how volume changes.
Problem: looked up table of coefficients of thermal expansion on Wikipedia. Value was disputed for
rubber, but it was around 450*10^-6 K^-1 for polypropylene (plastic). I figured that would be the closest
possible value to the squash ball because they are both polymers. Using the formula for thermal
expansion (𝑉𝑓 = 𝑉𝑖 ∗ 𝑒 ∝𝑣 ∆𝑡 ), I figured out that a temperature change required to produce a measureable
change in volume would be much too high to produce in lab. We are going to have to figure out some
other way to measure the coefficient of thermal expansion