1. Wave Notes…

2. What does the term medium mean?
What are the 2 types of waves and how are different? What is constructive interference? What is destructive interference?

3. Using a sine curve to represent waves of energy allows us to show several factors very easily

4. Sine Wave Crest=highest point Trough= lowest point
Node=resting point(s)
Wavelength= crest to crest
Amplitude= height of crest above node line
Frequency= # of cycles per second

5. Frequency is in the unit of Hertz (Hz)
1cycle per second = 1Hz
25 cycles per second = 25Hz

6. Some Constants… AM radio broadcasts on kHz frequency
FM radio broadcasts on a MHz frequency
Microwaves are n a gigahertz frequency

7. Energy waves are originated by some disturbance of a medium…
Medium is the “thing” the energy is moving through such as air, water, rock…
Wave speed is highly effected by the medium as well as the frequency and wavelength.

8. Vw = fλ Vw is velocity of the wave in m/s F is frequency in Hz
λ is wavelength in m
*** speed of light is always 3 x 108m/s***

9. This whole idea of using sine curves and waves leads to the concept of simple harmonic motion (patterns)

10. Example 1:
You are sitting on a dock and notice 2 waves crash onto the shore every second. You also notice that the space between wave crests is about 1.5 m.
What is the frequency?
What is the wavelength?
What is the velocity of the waves?

11. Example 2:
If red light has a wavelength of 7 x 10-7m. What is its frequency? (HINT: All light has the same speed regardless of color)

12. Another place we see simple harmonic motion (sine curves) is with mass spring systems like in a pin ball machine.
HOOKE’S LAW
Fe = -(k)(x)
K is the spring constant
X is displacement in m
F is force in newtons

13. Example 3:
If a 0.55kg mass is attached to a vertical spring that stretches 2 cm, calculate the spring constant.

14. Pendulums are another place we apply sine curves for understanding.
Remember that a pendulums swing is most dependant on the length of the pendulum, not mass hung!!
T= 2π√L/g T is period
L is length in m
g is 9.81m/s

15. Example4:
Calculate the period of a pendulum which a an arm length of 10 cm.

16. If frequency is inversely related to period…
What is the frequency of the pendulum from example 4?

17. Sometime pendulums and spring are found in the same simple machine, like a grandfather clock
T= 2π√m/k
m is mass in kg
k is the spring constant
T is period in seconds

18. Homework…
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