Presentation on theme: "Chapter 15: Oscillatory motion part 1"— Presentation transcript:
1Chapter 15: Oscillatory motion part 1 Reading assignment: ChapterHomework : (due Monday, Nov 7, 2005):Problems: 32, 33, 43, 45We’ll deal mainly with simple harmonic oscillations where the position of the object is specified by a sinusoidal (sine, cos) function.
2Two cups are filled to the same level with water. One of the two cups has ice cubesfloating in it. When the ice cubes melt, inwhich cup is the level of the water higher?1. The cup without ice cubes.2. The glass with ice cubes.3. It is the same in both.
3Two cups are filled to the same level with water. One of the two cups has plastic ballsfloating in it. If the density of the plastic ballsis less than that of ice, which of the two cupsweighs more?1. The cup without plastic balls.2. The cup with plastic balls.3. The two weigh the same.
4A boat carrying a large boulder is floating on a lake.The boulder is thrown overboardand sinks. The water level in the lake (withrespect to the shore)1. rises.2. drops.3. remains the same.
5A lead weight is fastened on top of a large solid piece of Styrofoam that floats in a containerof water. Because of the weight of thelead, the water line is flush with the top surfaceof the Styrofoam. If the piece of Styrofoamis turned upside down so that theweight is now suspended underneath it,1. the arrangement sinks.2. the water line is below the top surface ofthe Styrofoam.3. the water line is still flush with the topsurface of the Styrofoam.
6A lead weight is fastened to a large solid piece of Styrofoam that floats in a containerof water. Because of the weight of thelead, the water line is flush with the top surfaceof the Styrofoam. If the piece of Styrofoamis turned upside down, so that theweight is now suspended underneath it, thewater level in the container1. rises.2. drops.3. remains the same.
7Consider an object floating in a container of water. If the container is placed in an elevatorthat accelerates upward,1. more of the object is below water.2. less of the object is below water.3. there is no difference.
8Consider an object that floats in water but sinks in oil.When the object floats in water,half of it is submerged. If we slowly pour oilon top of the water so it completely coversthe object, the object1. moves up.2. stays in the same place.3. moves down.
9In the following section we assume: the flow of fluids is laminar (not turbulent) There are now vortices, eddies, turbulences. Water layers flow smoothly over each other.the fluid has no viscosity (no friction). (Honey has high viscosity, water has low viscosity)
10Equation of continuity For fluids flowing in a “pipe”, the product of area and velocity is constant (big area small velocity).Why does the water emerging from a faucet “neck down” as it falls?
11A circular hoop sits in a stream of water, oriented perpendicular to the current. If thearea of the hoop is doubled, the flux (volumeof water per unit time) through it1. decreases by a factor of 4.2. decreases by a factor of 2.3. remains the same.4. increases by a factor of 2.5. increases by a factor of 4.
13Black board example 15.7Homework 15.51Bernoulli’s lawWater flows through a horizontal pipe, and then out into the atmosphere at a speed of 15 m/s. The diameters of the left and right sections of the pipe are 5.0 cm and 3.0 cm, respectively.What volume of water flows into the atmosphere during a 10 min period?What is the flow speed of the water in the left section of the pipe?What is the gauge pressure in the left section of the pipe?
17Two hoses, one of 20-mm diameter, the other of 15-mm diameter are connected one behindthe other to a faucet. At the open endof the hose, the flow of water measures 10liters per minute. Through which pipe doesthe water flow faster?1. the 20-mm hose2. the 15-mm hose3. The flow rate is the same in both cases.4. The answer depends on which of the twohoses comes first in the flow.
18Simple harmonic motion/oscillation Block attached to a springMotion of a swingMotion of a pendulumVibrations of a stringed musical instrumentMotion of a cantileverOscillations of houses, bridges, …Clocks
19An object hangs motionless from a spring. When the object is pulled down, the sum ofthe elastic potential energy of the spring andthe gravitational potential energy of the objectand Earth.1. increases.2. stays the same.3. decreases.
20Simple harmonic motion/oscillation Restoring force:F = - k·xAcceleration:Acceleration and restoring force:proportional to xdirected toward the equilibrium position
21Simple harmonic motion/oscillation An object moves with simple harmonic motion whenever its acceleration is proportional to its displacement from some equilibrium position and is oppositely directed.w is angular frequency
22An object hangs motionless from a spring. When the object is pulled down, the sum ofthe elastic potential energy of the spring andthe gravitational potential energy of the objectand Earth.1. increases.2. stays the same.3. decreases.
23Properties of simple harmonic motion Position of particle at time t:A…amplitudew…Angular frequencyf…phase constant, phase angleT…period(wt + F)…phase
24Properties of simple harmonic motion The period T of the motion is the time it takes for the particle to complete one full cyclePeriodic motionThe value of x at time t is equal to the value of x at time t +T
25A person swings on a swing.When the person sits still, the swing oscillates back andforth at its natural frequency. If, instead, twopeople sit on the swing, the natural frequencyof the swing is1. greater.2. the same.3. smaller.
26A person swings on a swing.When the person sits still, the swing oscillates back andforth at its natural frequency. If, instead, theperson stands on the swing, the natural frequencyof the swing is1. greater.2. the same.3. smaller.
28The traces below show beats that occur when two different pairs of waves are added.For which of the two is the difference in frequencyof the original waves greater?1. Pair 12. Pair 23. The frequency difference was the samefor both pairs of waves.4. Need more information.
29Properties of simple harmonic motion Phase of velocity differs by – p/2 or 90° from phase of displacement.Phase of acceleration differs by – p or 180° from phase of displacement.
30Properties of simple harmonic motion Acceleration of particle is proportional to the displacement, but is in the opposite direction (a = - w2·x).Displacement, velocity and acceleration vary sinusoidally.The frequency and period of the motion are independent of the amplitude. (demo).
31Black board example 13.1An mass oscillates with an amplitude of 4.00 m, a frequency of 0.5 Hz and a phase angle of p/4.What is the period T?Write an equation for the displacement of the particle.Calculate the velocity and acceleration of the object at any time t.(d) Determine the position, velocity and acceleration of the object at time t = 1.00s.(e) Calculate the maximum velocity and acceleration of the object.
32The block-spring system The frequency depends only on:- the mass of the block- the force constant of the spring.The frequency does not depend on the amplitude.
33Black board example 13.2 (Problem 13.7) A spring stretches by 3.90 cm when a 10.0 g mass is hung from it. A 25.0 g mass attached to this spring oscillates in simple harmonic motion.Calculate the period of the motion.Calculate frequency and the angular velocity of the motion.