PPM: measurements Flashcards
precision of metre rule and measuring tape
to 0.1cm/1mm
both possible parallax error
precision of digital calipers
to 0.1mm. possible zero error
how to measure the volume of liquids (water & most liquids vs. mercury)
liquid level is curved in narrow glass cylinders into a ‘meniscus’ shape
position the eye at the bottom of the meniscus to avoid parallax error and read to 1/2 smallest division
most liquids would have a concave meniscus, similar to water. mercury has a convex meniscus and is an exception.
precision of measuring cylinders
half of smallest division on readings
precautions when using measuring cylinder
1) place the measuring cylinder on a flat surface (e.g. table top)
2) wait for the liquid in the measuring cylinder to settle down before reading
3) lower yourself down so your eye-level is aligned to the bottom of the liquid meniscus (or in the case of mercury top)
considerations when using displacement method to measure the volume of irregularly shaped objects
use either measuring cylinder or, if object cannot fit, a displacement can. object must be fully submerged in the water.
displacement method can only be used for waterproof objects/objects that do not absorb water. also assumes that volume of submerged string is negligible.
formula for density calculation
density = mass/volume
how density affects ability to float/sink in liquid
+ will the density of two differently sized objects made of the same material be the same?
all pieces of the same substance will have the same density regardless of shape or size
if the density of an object is higher than the density of the liquid it is being placed in, the object will sink. conversely, if the density of an object is lower than the density of the liquid it is being placed in, the object will float.
the denser the liquid an object is placed in, the higher the object will float in the liquid.
why would a ship made of iron float?
a ship is hollow and contains both iron and air. thus, the overall density of the ship is lower than the density of the seawater, causing it to float.
precision of electronic stopwatch
0.1s (even though stopwatches can record up to 0.01s, due to human reaction time)
