Ask+Mr.+Mitchell

Each edition, Mr. Mitchell fields questions about science topics related to our units of study. Have you got any questions for Mr. Mitchell? Send them to Ms. Inge at kinge@asd.edu.qa.

Here are this edition's questions and answers.

From Moustafa and Mohammed in G3
 * How much faster is light than sound? **

Mr. Mitchell's answer:  Since light and sound are both forms of kinetic energy they both move. Sound vibrations spread out in all directions like a wave on a lake, and light travels in a straight line. Compared to people, both light and sound move VERY fast. Their speed changes depending on what they are moving through, but let’s say you are comparing light and sound moving through air. Sound moves through air at a speed of about 343 meters per second. That means when you make a sound, the wave of air from that sound moves 343 meters away every second! That’s even faster than most airplanes, only jets like the Air France Concord that are “supersonic” can go faster than sound.  But light is even faster, in fact it’s not even close. Light moves through air at a speed of about 300 million meters per second! To travel 300 million meters you would have to walk around the Earth about 7 and a half times, and that’s just how far light travels every second! Light is by far the fastest thing we know of.

From Gabi in G3
 *  How fast can a guitar string move after you pluck it? **

Mr. Mitchell's answer:  When you pluck a guitar string it moves back and forth- this is called vibrating. If you’ve ever looked closely at a guitar string vibrating you’ve probably noticed it looks like a blur, because it’s moving very fast! How fast exactly? Well, it depends on which string you play- different strings vibrate at different speeds, and this difference in speed changes the pitch of the sound you hear. Faster vibrations make higher pitches and slower vibrations make lower pitches.  The thickest string on a guitar (the E string) has the slowest vibration. Still, it vibrates back and forth 82 times a second, which seems pretty fast to our eyes! The thinner the string, the faster it vibrates. The thinnest string on a guitar vibrates the fastest- back and forth about 330 times a second!

From Camilla and Ibraheem in G4
 *  If the Earth is magnetic, then why don’t magnets stick to the Earth? **

Mr. Mitchell's answer:  The Earth is magnetic, but it has a very weak magnetic field. How weak is it compared to the magnets we experiment with in school or the magnets on your refrigerator? Scientists can measure the strength of a magnet using a tool called a magnetometer. The strength of a magnet is measured in units called Teslas, named after the famous scientist Nikola Tesla, who made many discoveries and inventions with electromagnetism. An ordinary bar magnet that we use in school has a strength of about 10 milliTeslas. A large electromagnet used to lift things like old cars in a junkyard has a strength of about 1,000 milliTeslas, which is 100 times as strong! What about the Earth? If you measured the Earth’s magnetic field here in Qatar, it would only be about 0.03 milliTeslas. So the magnetic pull of an ordinary bar magnet is about 333 times as strong as the magnetic pull of the Earth, which is a good thing-- if the Earth’s magnetic field were stronger imagine how hard it would be to get anywhere in a car stuck to the ground! That’s why we only see the Earth’s magnetic field pulling very light things, like the needle of a compass.