Changing the measurement scale does not affect the extent to which the points tend to fall on a line. It would be the volume of water corresponding to a weight of zero, but zero is not a possible weigh t since the container itself weighs .5 pounds. The sample size of 10,000 would be more likely. With a small sample it is more likely to observe a strong relationship just by chance and thus more difficult to conclude that a relationship is statistically significant. A correlation of -.6 implies a stronger relationship.
Correlation measure only how closely the points fall to a straight line.
A perfect curved relationship may have a zero correlation since the points do not fall on or near any line. The intercept of .539 would represent the GPA of someone who got 0 for an SAT verbal score but that is impossible since the minimum SAT verbal score is 200.