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How to Calculate Density of Composite Objects

The density of an object is famously connected to the Greek scholar Archimedes, defining it simply as the mass of an object divided by its volume. Observing the water rising as he slipped into his bath, he realized that the water displaced must be linked to the volume of his body, allowing him to derive his weight precisely. He was so excited that he exclaimed the now-famous word "Eureka!" and ran through the streets naked. Today's modern materials are produced using complex methods creating composites, requiring a more rigorous method of measurement.

Things You'll Need

Wire of sufficient strength to support the suspension of the object measured
Newton meter (also known as a spring scale)
Distilled water
Water bath
Marker pen

Instructions

- 1
  Calibrate the newton meter. As newton meters use springs to calculate a weight, they can lose firmness over time. The scale on the meter uses a fixed length in accordance with Hooke's law and will produce increasingly less accurate results over time. Most newton meters have an adjustment nut for spring tension and will be supplied with a mass weighted in Newtons (the unit measurement of weight, 10 N is just under 2.25 lbs.). Hang the weight on the scale and turn the nut until the scale reads accordingly.
- 2
  Attach the object to the wire, preferably without using any attachments such as hooks or ties to lessen the impact of inaccuracies on the result. Tie the other end of the wire to the newton meter and suspend the object in free air, noting the weight when the spring has stopped bobbing and the meter is steady.
- 3
  Fill the water bath with enough water to submerge the object using fresh distilled water if available over tap water. Distilled water contains fewer impurities; the density of your object can be stated with higher certainty. If you have an electrical water bath, set the temperature to 73.5 degrees Fahrenheit / 23 degrees Celsius and not any higher -- the density of the water will drop dramatically as the temperature increases.
- 4
  Submerge the object into the water bath, immersing it completely along with around half the length of the connected wire. Note the weight on the newton meter and mark where the length of wire is submerged using the marker pen. Remove the object from the wire and dip the wire back into the bath, stopping when the water touches the mark. Read the newton meter and write down this figure also.
- 5
  Calculate the density of the object using all three values previously taken, using the following equation: Density = (A / (A + H - S)) * O, where A is the weight of the object in the air, H is the weight of the partially submerged wire, S is the weight of the object in the water and O is the density of the water used (0.998 for distilled, 0.995 to 0.996 for tap water).

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