Transcript BoomWhackers

BoomWhackers:
closed and open-ended pipes
Warmup (fill out on guided notes as you walk
in):
1) What is the speed of sound in a vacuum?_____
2) What is the speed of sound in air? ____
3) Remember the closed-pipe lab: How much of a
wavelength fit in a closed pipe: ½, 1/3, ¼, or 1/5?
(circle one)
4) On the next slide, label the node, antinode, draw the
wave, and label the wavelength of the sound...
Closed Pipe
Boom-Whackers Objectives
• SWBAT use what they have learned in the
waves unit (sound, standing waves, closed
pipes) to understand the function and
differences between closed and openended pipes.
Sound is Vibrating Air
Sound is produced by a vibrating object.
The vibrations of the object create particle
motions that cause pressure oscillations in
the air.
Vibrations of Air??
As the bell shown in the figure moves back and forth, the edge of the bell
strikes particles in the air.
When the edge moves forward, air particles are driven forward; that is the
air particles bounce off the bell with a greater velocity.
The result of these velocity changes is that the forward motion of the bell
produces a region where the air pressure is slightly higher than average.
The backward motion produces slightly below-average pressure.
Collisions among the air particles cause the pressure variations to move
away from the bell in all directions at the speed of sound.
A pressure variation that is transmitted through matter is a sound wave.
Vibrations of Air??
• The energy travels,
individual molecules
just vibrate.
• Compressions and
Rarefactions
• (Air gets alternately
squished together
then spread out)
Instruments work by vibrations
• Musical instruments such as gongs, cymbals, and drums are
examples of vibrating surfaces that are sources of sound.
In stringed instruments, such as the piano, guitar, and violin, wires
or strings are set into vibration. In the piano, the wires are struck; in
the guitar, they are plucked; and in the violin, the friction of the bow
causes the strings to vibrate.
The human voice is produced by vibrations of the vocal cords, which
are two membranes located in the throat.
In brass instruments, such as the trumpet and tuba, the lips of the
performer vibrate.
Reed instruments, such as the clarinet and saxophone, have a thin
wooden strip, or reed, that vibrates as a result of air blown across it.
More on the various instruments later...
Standing Waves in Pipes
• In flutes and organ pipes, air is forced
across an opening in a pipe. Air moving
past the opening sets the column of air in
the instrument into vibration.
• Like blowing across the top of a bottleFind the nodes and anti-nodes below:
Standing Wave
• A situation of maximum constructive
interference
• The other harmonics are heard, but we’ll
focus on the fundamental today (circle the
fundamental):
How to draw standing waves in
closed or open pipes:
• At a barrier, the air has the least freedom
to move: that is a node.
• At an end of the pipe, the air has the most
freedom to move: that is an antinode.
The Physics of Music
Standing Pressure Wave
If the reflected high-pressure wave reaches the tuning fork at the
same moment that the fork produces another high-pressure
wave, then the emitted and returning waves reinforce each
other.
This reinforcement of waves produces a standing wave, and
resonance is achieved.
See if you can figure it out without
the answer: On the next slide...
• Label the node and antinodes on each
pipe.
• Draw the corresponding wave and label
the wavelength.
• What fraction of the wave fits in a closed
pipe?___ An open pipe?___
• Which pipe makes a sound with a longer
wavelength?
Closed vs. Open Pipes
See if you are getting it....!
• The closed/open makes a sound with a longer
wavelength? (circle one)
• As wavelength goes up, frequency goes up/down (circle
one). (Use v=fλ)
• Frequency and pitch are related: high pitch means high
frequency and short wavelength.
low pitch means low frequency and long wavelength.
• Therefore, the closed/open pipe will make the lowest
sound (circle one).
• Ok.....Let’s Hear it!
Today’s Work:
• Let’s Play Music!
• Worksheet
• Closure (5 min before bell): On the halfsheet of paper on your table, write 3 things
you learned today and any questions you
still have; put in the inbox.
Objective and Closure:
• Today’s Objective: SWBAT use what they have
learned in the waves unit (sound, standing
waves, closed pipes) to understand the function
and differences between closed and openended pipes.
• Closure (5 min before bell): On the half-sheet of
paper on your table, write 3 things you learned
today and any questions you still have; put in the
inbox.