Why Things Float?

Why Things Float?

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/Volume

Density of water= 1.00(g/cm3) centimeters cubed

History: There is a well-known tale in which Archimedes was given the task of determining whether King Hiero's goldsmith was stealing the gold while assembling a wreath dedicated to the gods, and replacing the gold with a alloy. Archimedes knew the wreath could be crushed into a cube and the volume could be calculated easily and compared with the mass. The king did not approve of this idea. Archimedes decide he would take a bath as he immersed into the water in the tube the water rose and splashed out of the tub. Archimedes realized he could calculate the weight of the wreath by the displacement of water. Allegedly Archimedes forgot himself and ran naked through the streets yelling "Eureka!" Eureka!" This is said to be where we get the word "Eureka!" when we have a bright moment.

What Causes the Earth's Seasons?

The four seasons that are experienced on earth are caused by an interaction between the earth's tilt and the angle of sunlight that reaches the earth. To break this down it can be simply explained by saying the earth spins on an axis around the sun. In addition, the earth is also tilted at various degrees in relation to the sun. At certain times of the year the earth is tilted closer to the sun, which results in a higher portion of sunlight reaching the earth's surface. When this happens the northern hemisphere (which is where we live) is experiencing Summer! This means we have longer days and shorter nights. The sun is higher in the sky and more direct light reaches the earth. The opposite would be when the earth is tilted away from the sun. Then less sunlight would reach the earth, and this light is more spread out and not as direct. This would mean we are experiencing Winter! This means we have shorter days and longer nights. In between the two we have Spring and Fall. This is the time when the earth's tilt is starting to shift to one end of the extreme. In Spring earth's tilt is tracking back toward the sun, and in Fall the earth's tilt is starting to tilt away from the sun.

Cool Facts: The earth, which orbits around the sun once each year is tilted 23.5 degrees.
The sun crosses the celestial equator twice a year.
The spring equinox typically occurs around March 20-21.
The fall equinox typically occurs around September 22-23.
The summer solstice is June 21.
The winter solstice is December 21-22.

Typical Misconceptions: 1) Seasons have to do with the distance of earth from the sun. The seasons have nothing to do with the distance of earth from the sun! 2) Seasons are caused by earth's rotation on it's own axis ( the 24 hour cycle bringing night and day). Seasons are not caused by the earth's 24 hour rotation (based on which side of the earth is facing the sun)! 3) the sun rises and sets. Actually, instead the spot on earth where you are rotates to the morning!

A neat classroom activity:

Materials needed: apple, pencil, a large ball (ex: basketball), chart paper, and magic markers.

Demonstration: Place the large ball on a table. Tell students this represents the sun. Hold up the apple (stem facing upward), draw the equator around the middle of the apple with a magic marker. Tell students the apple represents the earth. Now poke the pencil through the apple from top to bottom and explain that the top where the stem of the apple is, is the area of the Northern Hemisphere. Ask students "If the earth is tilted on it's axis how should I tilt the (earth) apple?" When your apple (earth) is property tilted being sure to keep the pencil pointed in the same direction as you start to walk it (orbit) around the bigger ball (the sun). It is easier to keep the pencil facing the same wall. Do one full full orbit , then another and stop when the Northern Hemisphere is leaning toward the sun. Ask students "where is the Northern Hemisphere pointed?" Do you think the top of the apple (Northern Hemisphere) is warmer at this time of year?" If so why? Next, keep orbiting the apple until the Northern Hemisphere is pointed away from the sun (ball). Ask students "what do you think happens when the Northern Hemisphere points away from the sun?" "Is it colder?" Last have students think about the Southern Hemisphere ( the bottom part of the apple). Doing this experiment can be a way to provide a visual aid for teaching the reason for the seasons in the classroom!

The Phases of the Moon

We have all wondered what causes the moon to go through phases. The best way to understand this process is by looking at a moon-sun diagram. This can be accessed through using Google. The best way to describe the moon phases is to realize that exactly one half of the moon is always illuminated by the sun. This is perfectly logical; however, in order to understand this concept we should visualize this on a diagram. This can be accessed at http://www.moonconection.com/moon_phases . At certain times we see both the sunlit portion and the shadowed portion of the moon---and that creates the various moon phases we are all familiar with. The best explanation is that the lunar phases are created by changing angles (relative positions) of the earth, the moon and the sun, as the moon orbits the earth.
Moon phases can be simplified by understanding them in this order: new moon and full moon, first quarter and third quarter, and the phases in between. The new moon occurs when the moon is positioned between the earth and the sun. At this time the three objects are in approximate alignment. At full moon the earth, moon, and the sun are in approximate alignment, just as the new moon, but the moon is on the opposite side of the earth, so the sunlit part of the moon is facing us. The shadowed part is entirely hidden from view. The first quarter and third quarter moons (also called half-moons) occur when the moon is at a 90 degree angle with respect to the earth and the sun. This allows us to see exactly half of the moon illuminated and half of the shadowed part of the moon.
Other fun moon facts: After a new moon and the sunlit portion is increasing, but less than half this is called waxing crescent. After the first quarter the sunlit portion is still increasing, but now more than half this is called waxing gibbous. After the full moon light is decreasing, so this is called waning gibbous. Following the third quarter this is known as waning crescent. And then the cycle begins again!
Moon's Orbit: You may think it takes about one month for the phases of the moon to take place, but actually, it is exactly 29.5305882 days This is the time required for the moon to move to the same position as seen by an observer on earth. If you were to view the moon from outside our solar system (for example from the stars) the time required would be 27.3217 days roughly 2 days less. If you find this interesting then try to figure out why this is?