Thursday, April 14, 2011

Using Sound to "See" - Amazing Bats

Ever wonder how bats navigate so well during the night and even in the darkest of caves?  Bats don't have very good eyesight, instead they generate very high sounds and then listen for the echoes.  The echoes provide information on what is ahead - thus they "see" using sound instead of light.  This amazing feature is called "sonar".  Sonar is also used by the porpoise and by submarines.

In a bat–swarm, in cave or night air, a bat can know its own sound among thousands of mobile neighbours, detecting its own signals even if they are 2000 times fainter than background noises. It can “see” prey, such as a fruitfly, up to 100 feet away by echo location and catch four or five in a second. And this whole auditory system weighs a fraction of a gram! Ounce for ounce, watt for watt, it is millions of times more efficient and more sensitive than the radars and sonars contrived by man.  The bat “sees” with sound better than light.

Understanding and Demonstrating How Sounds are Produced

This week we are studying sound.   To demonstrate how sound works, we made devices that generate sounds with different frequencies.

Musical instruments are designed (and they are tuned) to produce tones with specific frequencies (notes).  Changing the length or the tension of a string on a piano, or guitar changes the frequency making it higher or lower.  On woodwinds, changing the length and diameter of a pipe will change the frequency. 

In these photos, we are cutting simple drinking straws to different lengths then blowing across them, showing that changes in length affect the sound.   Longer straws generate lower tones and shorter straws produce higher tones.

Scientists measure sound energy in units called decibels.  When humans hear a high sound (jet engine) and compare it to a low sound (waves crashing or thunder) of equal energy, do they perceive that higher frequency sounds are louder, lower frequency sounds are louder, or both the same?  Ask Mrs D to find out the answer!

MODEL ROCKETS COMING TO 5TH GRADE ! - But who is the inventor of modern rocketry?

Robert Goddard: A Man and His Rocket
On March 16, 1926, Robert Goddard successfully launched the first liquid-fueled rocket in Auburn, Mass. The first-of-its-kind rocket reached an altitude of 41 feet, lasted 2 seconds and averaged about 60 miles per hour. Dr. Goddard with one of his rockets
Goddard wrote in his autobiography about an inspiration that came to him as a boy while up in a cherry tree pruning branches: "I imagined how wonderful it would be to make some device which had even the possibility of ascending to Mars.... "

In 1907, while a student at Worcester Polytechnic Institute in Massachusetts, Goddard experimented on a rocket powered by gunpowder in the basement of the physics building. Clouds of smoke caused a lot of commotion and the faculty, rather than expel him, took an interest in his work.  (Caution: Dale County School System might not be quite as forgiving!)

In 1920, the Smithsonian published his original paper, "A Method for Reaching Extreme Altitudes," in which he included a small section stressing that rockets could be used to send payloads to the Moon. The next day, the New York Times wrote a scathing editorial denouncing his theories as folly.  He responded to a reporter's question by stating, "Every vision is a joke until the first man accomplishes it; once realized, it becomes commonplace."A day after Apollo 11 set off for the Moon, in July of 1969, the New York Times printed a correction to its 1920 editorial section, stating that "it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."

To read more, check out the following link: