MOTION , FORCES & ENERGY

MOTION, FORCES& ENERGY TAKS REVIEW OBJ. 5 IPC (5)

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

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.

Definitions • 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. FYI - In a wave, the energy moves through the medium, BUT THE OBJECT STAYS PUT (although it may oscillate).

Wave types MECHANICAL WAVES Need a medium to move through. Ex: sound, water, etc. ELECTROMAGNETIC WAVES Do not need a medium. Ex: light

How Waves Move Transverse Particles in the medium move perpendicular to the direction of the wave. Longitudinal (Compressional) Particles in the medium move parallel to the direction of the wave. Transverse & Longitudinal Waves in Action!!! (link)

Wave Characteristics Crest & Trough – the highest & lowest point, respectively, of a transverse wave. (Compressions & Rarefractions in longitudinal waves). Wavelength– the length of one complete wave cycle. (crest to crest, trough to trough)

Wave Characteristics Amplitude – the height measured from the resting line. Amplitude indicates the amount of in the wave. ENERGY

Wave Characteristics Frequency – the number of waves that pass a given point in one second. Measured in Hertz (Hz). Frequency determines the pitch of a sound. COUNTING waves

Wave Speed To calculate wavespeed/velocity (v), we need 1. Frequency (f) in Hertz (Hz) & 2. Wavelength (λ) in meters (m) Our formula is: Speed = frequency x wavelength v =fλ The units for speed are usuallym/s.

Problem 1: Wave types & characteristics Which illustration best demonstrates compression waves?

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.

Problem 3: Wave types & characteristics Which wave has the greatest velocity? V = ƒλ A. v = (2 Hz)(1 m) = 2 m/s B. v = (8 Hz)(2 m) = 16 m/s C. v = (3 Hz)(3 m) = 9 m/s D. v = (1 Hz)(4 m) = 4 m/s

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

Wave Interactions Constructive Interference– The addition of two or more overlapping waves that produced a wave of increased amplitude. Destructive Interference– The addition of two or more overlapping waves that produces waves of decreased amplitude.

INTERFERENCE PATTERNS FROM POINT SOURCE WAVES = + Nodes are areas of destructive interference(zero amplitude). Antinodes are the areas of constructive interference(2x amplitude). Two point source waves. Light rings are wave crests, dark rings are troughs.

Reflection The bouncing back of waves as they strike a barrier or encounter the boundary of another medium.

REFRACTION As waves pass into different mediums, they travel at different speeds and bend. 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.

DiffractionThe bending of a wave around a barrier, such as an obstacle or opening. 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.

Resonance When the frequency of a force applied to a system matches the natural frequency of vibration of the system and causes a dramatic increase in amplitude. CONSTRUCTIVE INTERFERENCE! AMPLIFIES SOUND!

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

Doppler EffectApparent change in the wave frequency (and pitch) 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 heard High pitch heard

Problem 4: Wave Interactions Polarized sunglasses are useful because – A. They are dark and don’t allow as much light to come through. B. They reflect much of the light from their surfaces. C. They filter out the horizontal transverse waves in light while allowing only the vertical waves to get to the eyes. D. They both diffract and refract light.

Problem 5: 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 A. Refract B. Interfere C. Reflect D. Polarize

Problem 6: 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

Problem 7: Wave Interactions 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? A. interference B. the Doppler effect C. resonance D. standing waves

MOTION , FORCES & ENERGY