1. Group Research and Teach
Section 19.1
Design a way to teach all important concepts and vocab (foldable, skit, class activity, story, rap, large flip book, magazine ad, video, digital presentation...no posters, no PPT)
Must be original…not copied from the book in any way. Be memorable.
Must include research information about an example of an oscillator that impacts society…what it is, how it works, why it’s important.
All member MUST BE SEEN ACTIVELY PARTICIPATING

2. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Vocabulary
phase
Objectives
Recognize the difference between
linear motion and harmonic
motion graphs.
Interpret graphs of harmonic
motion.
Determine amplitude and period
from a harmonic motion graph.
Recognize when two oscillators
are in phase or out of phase.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

4. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Reading harmonic motion graphs
Harmonic motion graphs show cycles
Typical graphs for linear motion (top) and harmonic motion (bottom).
Graphs of linear motion do not show cycles. Harmonic motion graphs show repeating
cycles.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

5. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
The most common type of graph puts position on the vertical (y) axis and time on the horizontal (x) axis. The graph below shows how the position of a pendulum changes over time. The repeating “wave” on the graph represents the repeating cycles of motion of the pendulum.
This pendulum has a period of 1.5 seconds so the pattern on the graph repeats every 1.5 seconds.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

6. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Determining period and amplitude from a graph
To find the period from a graph, start by identifying one complete cycle. The cycle must begin and end in the same place in the pattern.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

7. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Determine the period (the time it takes for one cycle to occur) of an oscillator from a graph by locating one full cycle and finding the time that it took. Find the frequency by taking the inverse of the period.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

8. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
On a graph of harmonic motion, the amplitude is half the distance between the highest and lowest points on the graph.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

9. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Figure 19.10: The amplitude is one-half the distance between the highest and lowest points on the graph. In this graph of harmonic motion, the amplitude is 20 centimeters.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

10. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Circular motion and phase
The phase tells you exactly where an oscillator is in its cycle. Phase is measured relative to the whole cycle and is independent of amplitude or period. One full cycle is always equal to 360 degrees.
Degrees and fractions are used to describe the phase of an oscillator.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

11. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
The concept of phase is most important when comparing two or more
oscillators. Imagine two identical pendulums. If you start them together, their graphs look like the picture below. We say these pendulums are in phase because their cycles are aligned. Each is at the same phase at the same time.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

12. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Harmonic motion that is out of phase
Hint: Always find where the second falls on the first
The two pendulums are 90 degrees out of phase.
The two pendulums are 180 degrees out of phase.
11/13/2018
Mr. Pike BHS Physics Mr. Yates

13. Mr. Pike BHS Physics Mr. Yates
Harmonic Motion
Chapter 19
19.2 Graphs of Harmonic Motion
Section Review
1. What is the difference between a graph of linear motion and a graph of harmonic motion?
2. A graph of the motion of a pendulum shows that it swings from +5 centimeters to -5 centimeters for each cycle. What is the amplitude of the pendulum?
3. A pendulum swings from -10 degrees to +10 degrees. What is the amplitude of this
pendulum?
4. A graph of harmonic motion shows that one cycle lasted from 4.3 seconds to 6.8 seconds. What is the period of this harmonic motion?
5. A graph of harmonic motion shows that the motion lasted for 10 seconds and it included 5 cycles. What is the period of this harmonic motion?
6. Sketch the periodic motion for two oscillators that are 45 degrees out of phase.
7. If one oscillator were out of phase with another oscillator by 45 degrees, what fraction of a 360-degree cycle would it be out of phase? 1/8, 1/4, 1/2, or 3/4?
11/13/2018
Mr. Pike BHS Physics Mr. Yates