1. PHYSICS 1 UNIT 3: WAVES PART 4: PENDULUMS, RESONANCE, REFLECTION AND REFRACTION MS. PACHECO SOUTH OLDHAM HS

2. VIBRATION OF A PENDULUM A STONE SUSPENDED AT THE END OF A STRING IS A SIMPLE PENDULUM. PENDULUMS SWING BACK AND FORTH WITH SUCH REGULARITY THAT THEY HAVE LONG BEEN USED TO CONTROL THE MOTION OF CLOCKS. THE TIME OF A BACK-AND-FORTH SWING OF THE PENDULUM IS ITS PERIOD. GALILEO DISCOVERED THAT THE PERIOD OF A PENDULUM DEPENDS ONLY ON ITS LENGTH—ITS MASS HAS NO EFFECT.

3. VIBRATION OF A PENDULUM TWO PENDULUMS OF THE SAME LENGTH HAVE THE SAME PERIOD REGARDLESS OF MASS.

4. VIBRATION OF A PENDULUM A LONG PENDULUM HAS A LONGER PERIOD THAN A SHORTER PENDULUM. IT SWINGS BACK AND FORTH MORE SLOWLY—LESS FREQUENTLY— THAN A SHORT PENDULUM. JUST AS A LONG PENDULUM HAS A GREATER PERIOD, A PERSON WITH LONG LEGS TENDS TO HAVE A SLOWER STRIDE THAN A PERSON WITH SHORT LEGS. GIRAFFES AND HORSES RUN WITH A SLOWER GAIT THAN DO SHORT- LEGGED ANIMALS SUCH AS HAMSTERS AND MICE.

5. FOUCAULT PENDULUM DESIGNING A PENDULUM WAVE

6. PERIOD OF A PENDULUM EQUATION

7. PENDULUM PRACTICE PROBLEM 1: HOW LONG DOES IT A 7.5 METER LONG PENDULUM TO MAKE A COMPLETE CYCLE? PROBLEM 2: IF THE PERIOD OF A PENDULUM IS 2.4 SECONDS, HOW LONG IS THE PENDULUM?

8. NATURAL FREQUENCY WHEN ANY OBJECT COMPOSED OF AN ELASTIC MATERIAL IS DISTURBED, IT VIBRATES AT ITS OWN SPECIAL SET OF FREQUENCIES, WHICH TOGETHER FORM ITS SPECIAL SOUND.

9. NATURAL FREQUENCY DROP A WRENCH AND A BASEBALL BAT ON THE FLOOR, AND YOU HEAR DISTINCTLY DIFFERENT SOUNDS. OBJECTS VIBRATE DIFFERENTLY WHEN THEY STRIKE THE FLOOR. WE SPEAK OF AN OBJECT’S NATURAL FREQUENCY, THE FREQUENCY AT WHICH AN OBJECT VIBRATES WHEN IT IS DISTURBED.

10. NATURAL FREQUENCY NATURAL FREQUENCY DEPENDS ON THE ELASTICITY AND SHAPE OF THE OBJECT. THE NATURAL FREQUENCY OF THE SMALLER BELL IS HIGHER THAN THAT OF THE BIG BELL, AND IT RINGS AT A HIGHER PITCH.

11. RESONANCE IF THE FREQUENCY OF A FORCED VIBRATION MATCHES AN OBJECT’S NATURAL FREQUENCY, RESONANCE DRAMATICALLY INCREASES THE AMPLITUDE. YOU PUMP A SWING IN RHYTHM WITH THE SWING’S NATURAL FREQUENCY.

12. RESONANCE TIMING IS MORE IMPORTANT THAN THE FORCE WITH WHICH YOU PUMP. EVEN SMALL PUMPS OR PUSHES IN RHYTHM WITH THE NATURAL FREQUENCY OF THE SWINGING MOTION PRODUCE LARGE AMPLITUDES.

13. Consider sound waves in a tube. When the prong of a tuning fork next to the tube moves toward the tube, a compression enters the tube. When the prong swings away, in the opposite direction, a rarefaction follows the compression. As the source vibrates, a series of compressions and rarefactions is produced. Sound in Air

14. a.The first compression gives the fork a tiny push. b.The fork bends. c.The fork returns to its initial position. d.It keeps moving and overshoots in the opposite direction. e.When it returns to its initial position, the next compression arrives to repeat the cycle. Resonance

15. RESONANCE IF THE FORKS ARE NOT ADJUSTED FOR MATCHED FREQUENCIES, THE TIMING OF PUSHES WILL BE OFF AND RESONANCE WILL NOT OCCUR. WHEN YOU TUNE A RADIO, YOU ARE ADJUSTING THE NATURAL FREQUENCY OF ITS ELECTRONICS TO ONE OF THE MANY INCOMING SIGNALS. THE RADIO THEN RESONATES TO ONE STATION AT A TIME.

16. RESONANCE RESONANCE OCCURS WHENEVER SUCCESSIVE IMPULSES ARE APPLIED TO A VIBRATING OBJECT IN RHYTHM WITH ITS NATURAL FREQUENCY. THE TACOMA NARROWS BRIDGE COLLAPSE WAS CAUSED BY RESONANCE. WIND PRODUCED A FORCE THAT RESONATED WITH THE NATURAL FREQUENCY OF THE BRIDGE. AMPLITUDE INCREASED STEADILY OVER SEVERAL HOURS UNTIL THE BRIDGE COLLAPSED.

17. RESONANCE THE TACOMA NARROWS BRIDGE

18. REFLECTION AND REFRACTION LIGHT DOESN’T TRAVEL THROUGH A MIRROR, BUT IS RETURNED BY THE MIRROR’S SURFACE. THESE WAVES ARE REFLECTED. WHEN WAVES STRIKE THE SURFACE OF A MEDIUM AT AN ANGLE, THEIR DIRECTION CHANGES. THESE WAVES ARE REFRACTED. USUALLY WAVES ARE PARTLY REFLECTED AND PARTLY REFRACTED WHEN THEY FALL ON A TRANSPARENT MEDIUM.

19. REFLECTION THE RETURN OF A WAVE BACK TO ITS ORIGINAL MEDIUM IS CALLED REFLECTION. FASTEN A SPRING TO A WALL AND SEND A PULSE ALONG THE SPRING’S LENGTH. THE WALL IS A VERY RIGID MEDIUM COMPARED WITH THE SPRING, SO ALL THE WAVE ENERGY IS REFLECTED BACK ALONG THE SPRING. WAVES THAT TRAVEL ALONG THE SPRING ARE ALMOST TOTALLY REFLECTED AT THE WALL.

20. REFLECTION A METAL SURFACE IS RIGID TO LIGHT WAVES THAT SHINE UPON IT. LIGHT ENERGY DOES NOT PROPAGATE INTO THE METAL, BUT INSTEAD IS RETURNED IN A REFLECTED WAVE. THIS IS WHY METALS SUCH AS SILVER AND ALUMINUM ARE SO SHINY. THEY REFLECT ALMOST ALL THE FREQUENCIES OF VISIBLE LIGHT.

21. REFLECTION IF YOU LOOK AT A BLUE SHIRT IN A MIRROR, WHAT IS THE COLOR OF ITS IMAGE? WHAT DOES THIS TELL YOU ABOUT THE FREQUENCY OF LIGHT INCIDENT UPON A MIRROR COMPARED WITH THE FREQUENCY OF THE LIGHT AFTER IT IS REFLECTED?

22. REFLECTION OF SOUND AN ECHO IS REFLECTED SOUND. MORE SOUND ENERGY IS REFLECTED FROM A RIGID AND SMOOTH SURFACE THAN FROM A SOFT AND IRREGULAR SURFACE. SOUND ENERGY NOT REFLECTED IS ABSORBED OR TRANSMITTED. THE STUDY OF THE REFLECTIVE PROPERTIES OF SURFACES IS ACOUSTICS.

23. REFLECTION OF SOUND WHEN WALLS ARE TOO REFLECTIVE, THE SOUND BECOMES GARBLED BECAUSE OF MULTIPLE REFLECTIONS OF SOUND WAVES CALLED REVERBERATIONS. WHEN THE REFLECTIVE SURFACES ARE MORE ABSORBENT, THE SOUND LEVEL IS LOWER, AND THE HALL SOUNDS DULL AND LIFELESS. IN THE DESIGN OF AN AUDITORIUM OR CONCERT HALL, A BALANCE BETWEEN REVERBERATION AND ABSORPTION IS DESIRED.

24. REFRACTION WHEN A WAVE THAT IS TRAVELING AT AN ANGLE CHANGES ITS SPEED UPON CROSSING A BOUNDARY BETWEEN TWO MEDIA, IT BENDS. REFRACTION IS THE BENDING OF A WAVE AS IT CROSSES THE BOUNDARY BETWEEN TWO MEDIA AT AN ANGLE.

25. REFRACTION OF SOUND SOUND REFRACTION OCCURS IN UNEVEN WINDS OR WHEN SOUND IS TRAVELING THROUGH AIR OF UNEVEN TEMPERATURE. ON A WARM DAY THE AIR NEAR THE GROUND MAY BE APPRECIABLY WARMER THAN THE AIR ABOVE. SOUND TRAVELS FASTER IN WARMER AIR, SO THE SPEED OF SOUND NEAR THE GROUND IS INCREASED. THE REFRACTION IS NOT ABRUPT BUT GRADUAL. SOUND WAVES TEND TO BEND AWAY FROM WARM GROUND, MAKING IT APPEAR THAT THE SOUND DOES NOT CARRY WELL.

26. REFRACTION OF SOUND

27. WHEN THE LAYER OF AIR NEAR THE GROUND IS COLDER THAN THE AIR ABOVE, THE SPEED OF SOUND NEAR THE GROUND IS REDUCED. THE HIGHER SPEED OF THE WAVE FRONTS ABOVE CAUSES A BENDING OF THE SOUND TOWARD EARTH. SOUND CAN THEN BE HEARD OVER CONSIDERABLY LONGER DISTANCES.

28. REFRACTION OF SOUND AT NIGHT, WHEN THE AIR IS COOLER OVER THE SURFACE OF THE LAKE, SOUND IS REFRACTED TOWARD THE GROUND AND CARRIES UNUSUALLY WELL.

29. REFRACTION OF LIGHT DUE TO THE REFRACTION OF LIGHT: SWIMMING POOLS APPEAR SHALLOWER, A PENCIL IN A GLASS OF WATER APPEARS BENT, THE AIR ABOVE A HOT STOVE SEEMS TO SHIMMER, AND STARS TWINKLE. THE DIRECTIONS OF THE LIGHT RAYS CHANGE BECAUSE OF REFRACTION.

30. REFRACTION OF LIGHT CHANGES IN THE SPEED OF LIGHT AS IT PASSES FROM ONE MEDIUM TO ANOTHER, OR VARIATIONS IN THE TEMPERATURES AND DENSITIES OF THE SAME MEDIUM, CAUSE REFRACTION.

31. REFRACTION OF LIGHT