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 Hooke’s Law F = -kx › The force exerted by a spring is equal to the spring constant times the distance the spring is compressed or stretched from its.

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Presentation on theme: " Hooke’s Law F = -kx › The force exerted by a spring is equal to the spring constant times the distance the spring is compressed or stretched from its."— Presentation transcript:

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2  Hooke’s Law F = -kx › The force exerted by a spring is equal to the spring constant times the distance the spring is compressed or stretched from its equilibrium  Potential Energy in a Spring PE sp =1/2 kx 2

3  A spring stretches by 18 cm when a bag of potatoes weighing 56 N is suspended from its end. › Determine the spring constant › How much elastic potential energy is stored in the spring when it is stretched this far?

4  Equilibrium – When the forces on an object are balanced or equal zero and the acceleration is zero.  Periodic Motion – Motion that repeats in a regular cycle  Simple harmonic motion – when the force on an object is directly proportional to the displacement of the object

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6  Period – (T) time for one complete cycle  Amplitude – maximum distance that the object moves from equilibrium (measured in radians or meters)  Frequency – (f) number of cycles or vibrations per unit of time (measured in hertz, Hz = s -1 )

7  Period of a Pendulum  Example: A pendulum with a length of 36.9 cm has a period of 1.22 s. What is the acceleration due to gravity at the pendulum’s location

8  Period of Spring  Example: The body of a 1275 kg car is supported on a frame by four springs. Two people riding in the car have a combined mass of 153 kg. When driven over a pothole, the frame vibrates with a period of s. For the first few seconds, the vibration approximates SHM. Find the spring constant of a single spring.

9  Swinging – How do you make yourself go higher?  Occurs when small forces are applied at regular intervals to a vibrating or oscillating object and the amplitude of the vibration increases.

10  Many objects have a natural frequency – vibrates in a regular pattern.  Resonance occurs when whenever a sound wave has the same frequency as the natural frequency of an object. The sound will cause the object with the same natural frequency to vibrate.

11  A disturbance that carries energy through matter or space.  Types of Mechanical Waves 1. Transverse Waves 2. Longitudinal Waves 3. Surface Waves  Mechanical Waves – Waves that require a medium.  Medium – A material that a disturbance travels

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14  Longitudinal Waves – disturbance is in the same direction or parallel to, the direction of the wave’s motion.  Transverse Wave – one that vibrates perpendicular to the direction of the wave’s motion

15 Longitudinal wave On a longitudinal wave the area squeezed together is called the compression. The areas spread out are called the rarefaction. The wavelength is the distance from the center of one compression to the center of the next compression.

16  Surface Waves – Lake or ocean; Longitudinal at the surface, the particles move in a direction that is both parallel and perpendicular to the direction of wave motion.

17  Wavelength ( ) – shortest distance that the wave pattern repeats OR distance from peak to peak or trough to trough  Phase – Same displacement and same velocity › A crest and trough are exactly 180 o out of phase.  Period – time for one wavelength (T)  Frequency - # of cycles per unit time (Hz)

18  Speed – displacement of wave peak over time.  Amplitude – the distance of the wave peak/trough to equilibrium  Crest – High Point of the wave  Trough – Low Point of the wave

19 Crest Trough

20  The amplitude of a wave is directly related to the energy of a wave.  The amplitude of a longitudinal wave is determined by the closeness of the longitudinal waves. The closer the longitudinal waves and the farther the rarefaction lines.

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22  The piano string tuned to middle C vibrates with a frequency of 264 Hz. Assuming the speed of sound in air is 343 m/s, find the wavelength of the sound waves produced by the string.

23  Wave Interferences › Superposition - when two or more waves come together, the result is the sum of the individual waves.

24  Constructive Interference – interference in which individual displacements on the same side of the equilibrium position are added together to form resultant wave

25  Destructive Interference – interference in which individual displacements on opposite sides of the equilibrium position are added together to form the resultant wave

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27  Free End  Fixed End

28  Free End  Fixed End

29 A. twice as big B. 1/2 as big C. Stays the same D. 1/4 times as big E. Not enough information to decide

30 A.A. B.B. c.c. D.D.Fixed end

31 Loose end A.A. B.B. c.c. D.D.

32 4. What is the period of this wave? a) t 1 b) t 2 c) t 2 -t 1 d) t 3 -t 1 e) None of the above t1t1 t2t2 t3t3 Amp time 0 t4t4

33 5.The picture shows “displacement as a function of location along a string” What is the wavelength (“ ”)? A B C D E none of these Remember X axis is position not time

34 Fundamentals of waves 6.The picture shows “displacement as a function of location along a string” What is the amplitude? Remember X axis is position not time A B C D E none of these

35 7. Looking at the following waveform, what is the period? assume it repeats itself over and over time (sec) 12 A.1 sec B. 2 sec C. 1 m/s D. 2 m/s E.Not enough information

36 8. Looking at that same wave, what is its speed? Time (sec) 12 A.1/2 m/s B.2 m/s C.5 m/s D.20 m/s E.Not enough information

37 9. The wavelength, λ, is 10 m. What is the speed of this wave? 1 Time (sec) A) 1 m/s B) just under 7 m/s C) 10 m/s D) 15 m/s E) None of the above/not enough info/not sure

38 10. Which one of the following is most likely to be impossible? A. Transverse waves in a gas B. Longitudinal waves in a gas C. Transverse waves in a solid D. Longitudinal waves in a solid E. They all seem perfectly possible

39 A. twice as big B. 1/2 as big C. Stays the same D. 1/4 times as big E. Not enough information to decide

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43 Diffraction also occurs when passing through a small opening. They diffract and spread out as they pass through the hole.

44  A wave pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere

45  Node – a point in a standing wave that always undergoes complete destructive interference and therefore is stationary  Antinode – a point in a standing wave, halfway between two nodes, at which the largest amplitude occurs


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