Project Boomilever wooden tower designed to hold maximum weight Electric vehicle electric-propelled car designed to go a specific distance Sounds of Music build an instrument to play specific notes/chords Robot Ramble build a robot to complete a specific set of tasks Wright Stuff self-propelled plane to fly furthest and/or longest (permission only) Science Olympiad Science Fair Egg-O-Naut launch an egg on a water-propelled rocket and return it safely to Earth Electric vehicle electric-propelled car designed to go a specific distance Elevated Bridge design and build the most efficient bridge to contest specifications Its About Time build a non-electrical time piece Trajectory design and construct a device capable of launching a projectile into a target area Pre-Class for Monday What is periodic motion? Hint: we have covered this beforelong time ago. Vibrations and Waves Chapter 14 Periodic Motion Any type of motion that repeats or has a cyclic pattern Examples: pendulum, spring, circular motion (including orbital mechanics) We will focus on the pendulum and spring Assume that all periodic motion is simple harmonic motion: the force added is directly proportional to the distance moved An object suspended by a string or rope that swings back and forth Maximum velocity occurs at the bottom of the swing (KE) Minimum velocity occurs at the top of the swing (PE) We define the period as the time it takes the object to travel from one side to the other and back T : period (s) L : length of string (m) Swinging Lab Objective Find the acceleration of gravity Materials Pendulum, stopwatch, meter stick, calculator Procedures Record L for your pendulum. Measure the period. Solve for g. How close to the actual value are you? If less than 10%, stop; otherwise, try again. Pre-Class for Tuesday At what point in the swing is the speed of a pendulum the greatest? Metal or plastic shaped in a spiral pattern, designed to store/release energy When compressed or stretched, elastic potential energy is stored Amount of force required to store energy is based on the spring constant Assume all springs obey Hookes Law F : restoring force (N) k : spring constant (N/m) x : distance stretched or compressed (m) PE : stored energy in spring (J) WAVE CHARACTERISTICS Waves:Waves: repeating disturbances that transfer energy through matter or space Crest:Crest: highest point of wave Trough:Trough: lowest point of wave Amplitude:Amplitude: distance from rest position to crest or trough Wavelength (measured in meters) Distance between two similar points on a wave Frequency (measured in Hertz) Number of wavelengths that pass a fixed point each second Wave speed (measured in meters per second) How fast a wave is traveling v = v : wave speed (m/s) wavelength (m) frequency (Hz) 2 TYPES OF WAVES LONGITUDINAL (COMPRESSIONAL) motion and oscillation are parallel ex. Sound TRANSVERSE motion and oscillation are perpendicular ex. Light, radio waves PRINCIPLE OF SUPERPOSITION Waves can algebraically interact with each other This interaction is called interference Destructive: waves subtract from each other Constructive: waves add to each other Ch 14 HW: p m J m m/s; 0.21 s m 84.See picture s a. b. c. Pre-Class for Wednesday What type of wave is a sound wave? List all that apply. Chapter 15 A. Longitudinal wave B. Surface wave C. Pressure wave D. Transverse wave Chapter 15 Sound (and Music) Intensity (measured in decibels) Amount of energy transmitted by a wave Loudness (measured in pain) Human perception of sound intensity Pitch (measured in Hertz) The relative high or low frequency of a sound wave Longitudinal wave (sound) Must have a medium (material) to travel through Points of highest pressure are the crests Points of lowest pressure are the troughs Distance between crests or troughs is the wavelength How you hear Middle Ear has the anvil, hammer, and stirrup. Inner ear has the cochlea. Resonant Frequency Breaking glass with sound http://www.youtube.com/watch?v=17tqXgvCN0Ehttp://www.youtube.com/watch?v=17tqXgvCN0E Tacoma Narrows Bridge http://www.youtube.com/watch?v=j-zczJXSxnwhttp://www.youtube.com/watch?v=j-zczJXSxnw Doppler Effect The change in frequency of a wave due to the motion of the source or receiver If the wave is moving closer to the receiver, the frequency (pitch) increases If the wave is moving away from the receiver, the frequency (pitch) decreases Doppler Effect Equation d = s (v v d ) / (v v s ) where d is the detector frequency (Hz) s is the source frequency (Hz) v is the speed of sound (m/s) v d is the speed of the detector (m/s) v s is the speed of the source (m/s) Prandtl-Glauert singularity XX km m x 10 4 Hz x 10 3 m/s dB change is equal to 10 times the pressure; Hz Hz; 356 Hz Hz; 263 Hz Pre-Class for Friday The changing of the frequency based on the movement of the source or detector is called the _____ _____. Pre-Class for Tuesday Reviewing for test. Pre-Class for Tuesday What is a pendulum, or what causes a pendulum to swing?