Find Out About Floating

Find Out About Floating
By: Tabbatha Monroe

Grade Level: 4th

Tennessee Science Standards:

GLE 0407. Inq. 1 Explore different scientific phenomena by asking questions, making logical predictions, planning investigations, and recording data.

GLE 0407.9.1 Collect data to illustrate that the physical properties of matter can be described with tools that measure weight, mass, length, and volume.

Background information: Archimedes of Syracuse was an ancient philosopher, inventor, astronomer, engineer, and one of the greatest mathematicians of all time. One day Archimedes was summoned to determine the volume of a new crown that had been made for King Hiero II. He was asked to ensure it was made from solid gold and did not contain silver or other imperfect materials by the goldsmith who fashioned it. The crown was in the shape of a laurel wreath, a most irregular shape and one whose volume could not be easily measured by traditional means. Archimedes was puzzled on how to solve the problem without damaging the crown. One day while taking a bath Archimedes noticed that the water level raised as he entered the bathtub and lowered back to it's original level when he got out of the bathtub. He realized that this effect could be used to determine the volume of the crown. When submerged, the crown would displace water that was equal to its volume. The density could be calculated by dividing the weight of the crown by the volume of water it displaced. Archimedes could then determine if the density was lower than that of solid gold, which would occur if cheaper quality metals were used. With this discovery, Archimedes jumped from the bathtub and took to the streets naked yelling "Eureka!" (Geek for "I have found it!"), forgetting all about the fact that he left his robe behind.

Introduction: An object will float in water if it displaces enough water, but how much water is enough? You can find this out by collecting the displaced water, and then weighing that water. The water should weigh the same as the floating object.


Materials:
kitchen scales, large jar, small jar, large pan, pitcher of water (I colored the water blue for visual effects)

First, make sure the scales are set to zero. Then, fill the jar with water and note its weight.
The weight of the jar filled with water is 23oz.

Float the small jar in the big jar. It displaces the water, which spills out into the dish. Once displacement occurs the volume of the water can be easily measured, as can the volume of the immersed object (in this case, our jar). The weight of the big jar does not change. It is still 23oz.

Carefully remove the big jar and the scale from the dish. Put the container on the scale and adjust them to zero. Pour in the water that had spilled into the dish. Write down the weight of the water in the pitcher (2oz). Remove the pitcher and reset the the scale to zero.

Now weigh the small jar that was floating in the big jar. You can see that it has the same weight as the water it displaced (2oz).

What is the science behind objects floating in water? The ability of an object to "float" when it is placed in a fluid is called buoyant force, and this is related to density. If an object is less dense than the fluid in which it is placed, it will float. If the object is more dense than the fluid, it will sink. Density which is a physical property of matter expresses a relationship of mass to volume, thus the more mass an object contains in a given space, the denser it is. The formula: Density=Mass/VolumeDensity of water= 1.00(g/cm3) centimeters cubed