Lesson 3
OSCILLATORS
Announcements
Physics lab is NOT meeting this week
 Exam repair will be Friday
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HW #2 due TODAY
 HW #3 due tomorrow
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AP Physics B Standards
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I.F.1. Simple harmonic motion
Students should understand simple harmonic motion, so they can:
a) Sketch or identify a graph of displacement as a function of time, and
determine from such a graph the amplitude, period, and frequency of
the motion.
b) Write down an appropriate expression for displacement of the
form A sin t or A cos t to describe the motion.
e) State and apply the relation between frequency and period.
Lesson Objectives
LESSON 3:
Oscillation
Students will be able to:
1.
calculate the angular velocity of an object in periodic motion.
2.
describe periodic motion in terms of sinusoidal functions.
3.
identify the parts of a wave and determine potential and kinetic
energies at various points in time.
4.
relate frequency and period.
Periodic Motion
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Motion that repeats itself over a fixed and
reproducible period of time is called periodic
motion.
The revolution of a planet about its sun is an
example of periodic motion. The highly
reproducible period (T) of a planet is also called
its year.
Mechanical devices on earth can be designed to
have periodic motion. These devices are useful
timers. They are called oscillators.
Oscillator Demo

Let’s see demo of an oscillating spring using
DataStudio and a motion sensor.
Simple Harmonic Motion
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You attach a weight to a spring, stretch the spring past its
equilibrium point and release it. The weight bobs up and
down with a reproducible period, T.
Plot position vs time to get a graph that resembles a
sine or cosine function. The graph is “sinusoidal”, so the
motion is referred to as simple harmonic motion.
Curvefitting reveals the equation x = A sin (t)
Springs and pendulums undergo simple harmonic motion
and are referred to as simple harmonic oscillators.
Analysis of graph
Equilibrium is where kinetic energy is maximum and
potential energy is zero.
3
equilibrium
2
-3
x(m)
4
6
t(s)
Analysis of graph
Maximum and minimum positions
3
2
-3
x(m)
4
6
t(s)
Maximum and minimum positions have maximum
potential energy and zero kinetic energy.
Oscillator Definitions

Amplitude
◦ Maximum displacement from equilibrium.
◦ Related to energy.
◦ Unit: m

Period
◦ Length of time required for one oscillation.
◦ Unit: s

Frequency
◦ The number of cycles of oscillation completed in one
second.
◦ f = 1/T
◦ Unit: Hz or s-1
Sample Problem 3.2: An air‐track glider is attached to a spring oscillates between the 10 cm mark and the 60 cm mark on the track. The glider completes ten oscillations in 33 s. What are the (a) period, (b) frequency, (c) amplitude, and (d) maximum speed of the glider?
Sample Problem 3.3: An object in simple harmonic motion has an amplitude of 4.0 cm and a frequency of 2.0 Hz. Draw a position‐time graph showing two cycles of the motion. Identify the points where potential or kinetic energy are maximum.