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MOTION , FORCES & ENERGY

MOTION , FORCES & ENERGY. TAKS REVIEW. IPC (5) The student knows the effects of on everyday life. waves. Definitions Anyone?. WAVE - a transfer of energy, usually through a medium. MEDIUM –the substance that a wave moves in. OSCILLATION – to swing or move regularly back and forth.

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MOTION , FORCES & ENERGY

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  1. MOTION, FORCES& ENERGY TAKS REVIEW

  2. IPC (5) The student knows the effects of on everyday life. waves

  3. Definitions Anyone? • WAVE - a transfer of energy, usually through a medium. • MEDIUM –the substance that a wave moves in. • OSCILLATION – to swing or move regularly back and forth. • PROPIGATION – to transmit or move through a medium. • PERIODIC MOTION – motion that is repetitive over a given time interval. • FYI - In a wave, the energy moves through the medium, BUT THE OBJECT STAYS PUT (although it may oscillate).

  4. The student is expected to: • 5A: demonstrate wave types and their characteristics through a variety of activities such as modeling with ropes and coils, activating tuning forks, and interpreting data on seismic waves.

  5. TYPES OF WAVES MECHANICAL WAVES Need a medium to propagate. (sound, water, etc.) ELECTROMAGNETIC WAVES Do not need a medium to propagate in. (light)

  6. HOW WAVES PROPIGATE Transverse (S-Wave) Waves in which the oscillation of the medium is perpendicular to the propagation of the wave. Longitudinal (P-Wave or Compression) Waves in which the oscillation of the medium is parallel to the propagation of the wave. Transverse & Longitudinal Waves in Action!!! (link)

  7. Wave Characteristics Crest & Trough – the maximum displacement of the medium form the equilibrium position (Compressions & Rarefractions in longitudinal waves). Wavelength – the length of one complete wave cycle. (e.g. – crest to crest, trough to trough)

  8. HOW WAVES PROPIGATE Wavelength, Compressions & Rarefractions in longitudinal waves correspond to wavelengths, crests & troughs in transverse waves.

  9. Wave Characteristics Amplitude – refers to the distance the medium oscillates from equilibrium. Amplitude indicates the amount of in the wave. ENERGY

  10. Wave Characteristics TIMING A wave Wave Period – the time it take for one complete wave cycle to pass by a given point. T = sec/1 cyc COUNTING waves Frequency – the number of cycles that pass by a given point in a given amount of time. ƒ = cyc/1 sec Frequency & Period are related

  11. !!! WAVE EQUATIONS !!! V = d/tvelocity = distance / time V = ƒλvelocity = frequency * wavelength Both are measured in meters/second (m/s).

  12. Some Problems • Q1.   A sound wave has a frequency of 3250 Hzand a wavelength of  0·1 m. What is its velocity? A1.  Use  v = f x l v = 3250 x 0·1= 325 m/s. • Q2.   A sound wave travels with a velocity of 330 m/sand has a frequency of 500 Hz.  What is its wavelength? A2.  Use  l = v ÷ f   l = 330 ÷ 500= 0·66 m. • Q3.  A wave at sea travels with a velocity of 25 m/s.If it has a wavelength of 10 m, what is its frequency? A3.  Use f = v ÷ l f = 25 ÷ 10  = 2·5 Hz. • Note - always make sure that you give the units for your answerand that the units are correct.If the wavelength is given in centimeters,convert it to meters before doing the calculation.

  13. The student is expected to: • 5B: demonstrate wave interactions including interference, polarization, reflection, refraction, and resonance within various materials.

  14. SUPERPOSITION PRINCIPLE & INTERFERENCE(amplitude addition) Superposition Principle – The total displacement (amplitude) caused by two or more waves occupying the same space in a medium is equal to the sum of the displacements (amplitudes) of each of the individual waves. Constructive Interference(link) – The addition of two or more overlapping waves that produced a wave of increased amplitude. Destructive Interference(link) – The addition of two or more overlapping waves that produces waves of decreased amplitude.

  15. INTERFERENCE PATTERNS FROM POINT SOURCE WAVES = + Nodes are areas of destructive interference (in this case, 0 amplitude). Antinodes are the areas of constructive interference (in this case twice the amplitude). Two point source waves. Light rings are wave crests, dark rings are troughs.

  16. Reflection The bouncing back of waves as they strike a barrier or encounter the boundary of another medium. Fixed End Reflections are inverted. Free End Reflections are upright. Boundary Behavior Reflections are inverted if the new medium is more dense and upright if the new medium is less dense.

  17. Law of Reflection Law or Reflection – Angle of incidence = Angle of Reflection All angles are measured with respect to the normal Normal– dotted line drawn perpendicular to the surface where the light ray hits the reflecting surface

  18. REFRACTION The changing direction of waves as they pass into different mediums. Check this out!(link) When a wave enters a new medium, the change in density of a new medium causes the wave to travel at a different speed. If the new medium is more dense, the wave will slow down and bend toward the “normal.” If it is less dense the wave will speed up, and bend away from the “normal.”

  19. DiffractionThe bending of a wave around a barrier, such as an obstacle or opening. Occurs when a wave passes an edge, passes through a narrow gap or goes past an object. None of the properties of a wave are changed by diffraction. The wavelength, frequency, period and speed are same before and after diffraction. The only change is the direction in which the wave is traveling.

  20. Resonance a condition that exist when the frequency of a force applied to a system matches the natural frequency of vibration of the system that causes a dramatic increase in amplitude. THINK, “CONSTRUCTIVE INTERFERENCE.” AMPLIFIES SOUND!

  21. Doppler EffectApparent change in the wave frequency due to motion of wave source and/or observer. As sound is emitted from a moving object, the wave length behind the object appears to lengthen - the wave length in front of the object appears to decrease. Low Pitch Observed High Pitch Observed

  22. Sonic Boom

  23. Polarization • A method of reducing the number of planes that light waves are vibrating in. • Polarizing sun glasses reduce glare by blocking light waves vibrating in a certain direction. http://www.polarization.com/water/glare-tacho_movie.gif

  24. Problem 2: Wave types & characteristics Which of the following is not true about a wave? • Its energy increases as its amplitude increases. • Its frequency increases as its wavelength decreases. • Its velocity is equal to its frequency times its wavelength. • It transfers the particles of the medium along with the energy created by the disturbance.

  25. Problem 3: Wave types & characteristics The pitch of a sound made by plucking a guitar string is determined by the — A* frequency of the vibration produced B strength of the plucking force C distance between the strings D shape of the guitar body

  26. Problem 4: Wave types & characteristics Which of these tools is most useful in identifying the wavelengths of visible light? F Convex lens G Spectroscope H Microscope J Concave mirror

  27. Problem 5: Wave types & characteristics Which of the following would explain why this film works with a reduced amount of light? A The film reflects long wavelengths of light efficiently. B Fewer silver halide granules are present in the film. C The film refracts brighter light. D The photochemical reaction can occur in lower intensity light.

  28. Problem 6: Wave types & characteristics Which wave has the greatest velocity?

  29. Problem 7: Wave types & characteristics At 0°C sound travels through air at a speed of 330 m/s. If a sound wave is produced with a wavelength of 0.10 m, what is the wave’s frequency? F 0.0033 Hz G 33 Hz H 330 Hz J* 3300 Hz

  30. Problem 8: Wave Interactions The diagram shows waves approaching a barrier. Which pattern will be formed after the waves pass through the opening in the barrier?

  31. Problem 9: Wave Interactions Polarized sunglasses are useful because – F. They are dark and don’t allow as much light to come through. G. They reflect much of the light from their surfaces. H. They filter out the horizontal transverse waves in light while allowing only the vertical waves to get to the eyes. J. They both diffract and refract light.

  32. Problem 10: Wave Interactions Dolphins and bats use echolocation to hunt prey. They determine the distance to their prey by sending sound waves out and measuring the time it takes for the sound wave to return. This demonstrates the ability of sound waves to • Refract • Interfere • Reflect • Polarize

  33. Problem 11: Wave Interactions This graph shows the absorption spectrum for a certain pigment molecule. To a human, this pigment would most likely appear — A blue B green C* yellow D orange

  34. Problem 12: Wave Interactions When trying to spear a fish in water, a person needs to take into account the way light bends as it moves from water into air. The bending of light as it passes from one medium into another is known as — F reflection G* refraction H diffraction J polarization

  35. Problem 13: Wave Interactions One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because of — -or- A guitar player is seated next to a piano. The piano player strikes an E key on the piano. The guitarist reports that this causes the E string on his guitar to vibrate. What is the name of this phenomenon? F interference G the Doppler effect H* resonance J standing waves

  36. Problem 14: Wave Interactions What provides evidence that white light is actually a combination of all the colors? • An array of colors is seen when white light has moved through a prism. • The wavelengths of colored light are different. • All colored light refracts the same amount. • All colored light has the same wavelength.

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