TOPIC 4: PHYSICS

TOPIC 4: PHYSICS

1. ULTRASOUND

   • SOUND WITH FREQUENCIES HIGHER THAN 20,000 Hz (20 kHz)
     • ABOVE AND BEYOND THE HEARING RANGE OF HUMANS
   • THE WAVES GET PARTIALLY REFLECTED AT A BOUNDARY BETWEEN MEDIA BECAUSE OF THE CHANGE IN DENSITY (PARTIAL REFLECTION)
     • THE TIME IT TAKES FOR THER EFLECTION TO REACH THE DETECTOR CAN BE USED TO MEASURE HOW FAR AWAY THE BOUNDARY IS
   • USES
     • PRE-NATAL SCANNING OF A FOETUS ( SAFER THAN X-RAYS)
     • SONAR USED BY BOATS TO DETECT OTHER BOATS, MARINE ANIMALS, THE SEA BED AND ROCKS

2. INFRASOUND

   • SOUND WITH FREQUENCIES LESS THAN 20 Hz
     • BELOW THE HEARING RANGE OF HUMAN
   • USES
     • USED BY ANIMALS TO COMMUNICATE ( ELEPHANTS, BATS, TIGERS) THEY CAN DIFFRACT AROUND OBJECTS EASILY( LONG DISTANCES)
   • PRODUCED BY METEOR STRIKES AND VOLCANIC ERUPTIONS

3. THE EARTHS STRUCTURE

   • CRUST
     • MANTLE
       • OUTER CORE
         • INNER CORE
           • SOLID AND IS THOUGHT OF TO BE MADE OF IRON AND NICKEL
         • LIQUID
       • HAS PROPERTIES OF A SOLID EXCEPT THAT IT CAN FLOW VERY SLOWLY. RADIOACTIVE DECAY OCCURS IN THE MANTLE
     • WE LIVE ON IT BUT IT'S VERY THIN (ABOUT 20KM)
   • MADE UP OF TECTONIC PLATES
     • THEY FLOAT ON TOP OF THE MANTLE AND MOVE A FEW CM PER YEAR
       • AT PLATE BOUNDARIES THE PLATES MAY SLIDE PAST EACH OTHER WHICH SOMETIMES CAUSES EARTHQUAKES
         • THEY ARE VERY HARD TO PREDICT

4. SEISMIC WAVES

   • CAUSED BY EARTHQUAKES AND EXPLOSIONS
     • WE DETECT THESE WAVES ALL OVER THE SURFACE OF THE EARTH USING SEISMOMETERS
   • 2 TYPES
     • P-WAVES
       • THEY ARE LONGITUDINAL, FASTER THAN S-WAVES AND CAN TRAVEL THROUGH LIQUIDS AND SOLIDS
     • S-WAVES
       • THEY ARE TRANSVERSE ARE SLOWER THAN P-WAVES AND CAN ONLT TRAVEL THROUGH SOLIDS
   • REFLECT AND REFRACT AT BOUNDARIES BECAUSE OF THE DIFFERENT LAYER IN THE EARTH ( DIFFERENT DENSITIES)
   • SEISMOMETER RESULTS (SEISMOGRAMS)
     • YOU CAN WORK OUT THE EPICENTRE ( CENTRE OF THE EARTHQUAKE)
       • ON THE READINGS YOU CAN TELL WHICH IS THE P-WAVE AND S-WAVE ASTHE P-WAVE IS THE QUICKEST AND WILL ARRIVE FIRST
         • TRIANGULATION IS USED TO DETECT WHERE THE EARTHQUAKE'S EPICENTRE