Relative Motion

The laws of physics which apply when you are at rest on the earth also apply when you are in any reference frame which is moving at a constant velocity with respect to the earth. For example, you can toss and catch a ball in a moving bus if the motion is in a straight line at constant speed.

The motion may have a different appearance as viewed from a different reference frame, but this can be explained by including the relative velocity of the reference frame in the description of the motion.

Reference: http://hyperphysics.phy-astr.gsu.edu/hbase/relmot.html

If you are on a subway train in a subway station, you can see people standing or sometimes walking in the aisles of another train; your train or the other train might be moving in either direction. Sometimes it is hard to say what is moving! This means that the motion of a body always depends on a particular frame of reference. Galileo was the first person to formalize this concept, which is known as relative motion.

Click on website to see reletive motion in subway station demonstrations.

Refence: http://demonstrations.wolfram.com/RelativeMotionInASubwayStation/

(Galileo Galilei; 15 February 1564 – 8 January 1642) was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. )

(http://en.wikipedia.org/wiki/Galileo_galilei)

DIFFERENCE BETWEEN LIME AND LEMON

* A lemon is yellow and a lime is green!

* Limes are smaller than lemon

* Limes contain more acid than lemons, and are more sour (but lemons are small, green and more bitter before they mature and then turn yellow and more sweet when they mature. So what's the difference between a lime and an immature lemon?

* When put into a glass or bowl of water, a lime will sink to the bottom, and a lemon will float on the top. Could the difference in density be due to a difference in sugar content or a difference in lipid (oil) content? Lipids are less dense than water. Lemons are known for their lemon oil. Cut a lemon and feel the oil on the surface. A small, dense, green, immature lemon floats in water!

Reference: http://qna.rediff.com/questions-and-answers/what-is-the-difference-between-lime-lemon/12776448/answers

Cartesian Diver

Experiment description

The Cartesian diver experiment is set up by placing a "diver"—a small, rigid tube, open at one end, such as an eyedroper—in a much larger container with some flexible component; for example, a two liter soft drink bottle. The larger container is filled with water, and must be airtight when closed. The "diver" is partially filled with a small amount of water, but contains enough air so that it is nearly neutrally buoyant, but still buoyant enough that it floats at the top while being almost completely submerged.

The "diving" occurs when the flexible part of the larger container is pressed inward, causing the "diver" to sink to the bottom until the pressure is released, when it floats again.

Explanation of the principles at work

Air in the diver makes it neutrally buoyant and therefore float at the water's surface. As a result of Pascal's Principle, when the pressure increases by squeezing the container, the least dense material, the air in the diver, is affected. Thus, the pressure on the water increases the pressure on the air bubble in the diver. The air compresses and reduces in volume, permitting more water to enter the diver. The diver now displaces a lesser weight of water than its own weight and becomes negatively buoyant (i.e. sinks), according to Archimedes' principle. When the pressure on the container is released, the air expands again, increasing the weight of water displaced and the diver again becomes neutrally or positively buoyant and floats. If however, the buoyant force is equal to the compressed air force inside the diver, it will either float straight to the top or it will float in the middle of the container.

Reference: http://en.wikipedia.org/wiki/Cartesian_diver

THE DEAD SEA

The Dead Sea ,also called the Salt Sea, is a salt lake bordering Israel and the West bank to the west, and Jordan to the east.

The Dead Sea is 67 kilometres (42 mi) long and 18 kilometres (11 mi) wide at its widest point. It lies in the Jordan Rift Valley, and its main tributary is the Jordan River.

The Dead Sea is 378 m (1,240 ft) deep, the deepest hypersaline lake in the world. It is also one of the world's saltiest bodies of water, with 33.7% salinity. It is 8.6 times more salty than the ocean.

As the concentration of salt in the dead sea is very high, we are less dense than the Dead sea and hence, are able to float.

In recent decades, the Dead Sea has been rapidly shrinking because of diversion of incoming water from the Jordan River to the north. The southern end is fed by a canal maintained by the Dead Sea Works, a company that converts the sea's raw materials. From a depression of 395 m (1,296 ft) below sea level in 1970 it fell 22 m (72 ft) to 418 m (1,371 ft) below sea level in 2006, reaching a drop rate of 1 m (3 ft) per year. As the water level decreases, the characteristics of the Sea and surrounding region may substantially change.

Reference:

http://enwikipedia.org/wiki/Dead_Sea

What caused the Dead Sea's formation?

The Dead Sea depression is a continuation of the Rift Valley depression , which was caused, millions of years ago, by continental drift. Because of the low rainfall in the catchment area of the Dead Sea, there is not enough water flowing into the sea for it to flow out, south to the gulf - so we have an inland sea. The Jordan River continually brings small amounts of salt into the sea. Since there is no outflow, the salt level gradually built up over the millions of years, until the Dead Sea is now so salty that fish can not survive in it - hence the name.

Reference:

http://wiki.answers.com/Q/What_caused_the_Dead_Sea's_formation

How to find the volume of a cork?

AIM: to find the volume of a piece of cork.

APPARATIES: a displacement can, wooden block, beaker, measuring cylinder, sinker (ex. pebble) ,a piece of cork and piece of string.

ACTIVITY:

1. Set up the appartus.(put the displacement can on the wooden block and place the beaker close to the wooden block~under the displacement can's sprout~
2. Fill the displacement can with water and allow excess water to flow into the beaker.~discard this water, u don't need it~
3. Place the dry measuring cylinder directly below the sprout.
4. Tie the stone to the string and lower it carefully into the displacement can.
5. Allow the displaced water to collect in the measuring cylinder.
6. The amount of water collected is the volume of the stone. record it as VOLUME A.
7. Remove the stone from the displacement can and repeat steps 2 & 3.
8. Tie the cork on the same string you used to tie the stone and lower both of them carefully into the displacement can.
9. Allow the displaced water to collect in the measuring cylinder and record it as VOLUME B.
10. The difference between volumes A & B ,is the volume of the cork.

Reference: http://wiki.answers.com/Q/How_do_you_find_the_volume_of_an_irregular_shape_which_floats

How do submarines float and sink?

There are ballast tanks in a submarine. It is full of compressed air, and thus it floats. When the submarine wants to sink, the air is replaced by seawater. The weight of the submarine is now becoming greater than the weight of the amount of water it displaces. If it wants to stay at a constant depth, then the seawater/compressed air is balanced at a constant level. When it wants to rise to the surface again, the seawater is let out and the ballast tanks is once more full of compressed air.

http://wiki.answers.com/Q/How_does_a_submarine_sink_and_float

Thus, when seawater enters the ballast tanks, the density of the submarine will be denser than water and when seawater in the tanks is replaced by air, the density of the submarine will be less dense than the seawater in its surroundings and hence, it will float.

Why does an intact orange float but a peeled orange sink?

(picture edited)

Basically, it is because the skin of an orange is porous and contains airbags. It traps air which causes the density of an orange to be denser than water. When the orange is peeled, it loses its buoyancy, the density of the remaining parts of the orange(pulps) , which consist of water and solid masses, is denser than water and will sink.