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The Sound of
Gravity
The Upside-Down
Glass of Water
The Clinging
Water
Is It Coming or
Going?
The Pepsi Ghost
The Suspended
Hammer
The Hoover Bugle
Heavy Air
A Quick Pull
Is A Break For Newton
The Fiddler on
the Door
Pitch Pipe
A Hot Tone
Staying Dry
Under Water
The Soda
Fountain Band
The
Collapsing Can
Why Do We Need
Two Eyes?
Are You Left
or Right Sighted?
The Bubbling
Leaf
The Soda Can
Cannon
The Heavyweight
Grape
The Black Banana
The Heat Stretch
The Leprechaun In
A Bottle
MATERIALS:
- two sets of seven clamp-on lead weights (ball sinkers)
- two, 250 cm strong thin threads (nylon fish line)
- two metal cookie sheets
PROCEDURE:
- Clamp the seven weights exactly 30 cm from each other on the
thread and tape the end of the thread to the cookie sheet, such that the first (lowest)
washer is 30 cm above the surface.
- place cookie sheet on supports so that it is a few inches off of
the floor (this will improve the sound produced by the dropping weights)
- Stand on a chair and hold the line tight above the cookie sheet.
Release the thread and note the rhythm of the sound as the weights hit.
- Clamp the seven other weights to the other thread the following
distances from each other: cookie sheet to first weight 5 cm, the next six weights: 15,
25, 35, 45, 55, and 65 cm from each other respectively.
- Repeat step #3.
- Repeat both demonstrations, alternately, several times.
QUESTIONS:
- What kind of tapping sound (even intervals or faster and faster)
did the weights give in the first demonstration? In the second?
- Which of the weights had the highest velocity when hitting the
bottom?
- What kind of motion is the free fall of the weights?
- What gives a falling object its acceleration?
RATIONALE: The falling weights are all
subjected to gravity. The force of gravity imparts an accelerated motion to each of the
weights. Newton's Second Law states that F = MA (F = force, M = mass, and A =
acceleration). Because the force and mass of the weights are equal, the acceleration of
each of the weights is the same. The difference is that the further the weight falls, the
greater the velocity (v = at) of the weight when it hits the cookie sheet.
The distances between weights in the second demonstration were
obtained from:
2
d = 1/2 gt ( d = distance, g = accel. of gravity and t = time).
When the weights are placed at regular intervals, the arrival
is irregular, getting faster and faster, due to increased velocity (acceleration of
gravity X time). The weights in the second demonstration also have equal increasing
velocity, but because of the increased distance between weights, they arrive at even
intervals.
APPLICATION: A falling object increases
velocity proportional to the time of fall. A high fly ball goes up and comes down faster
than a pop fly.
MATERIALS:
- A transparent glass or plastic cup
- A stiff paper card (slightly larger than the mouth of the cup)
PROCEDURE:
- Fill the cup 3/4 full with water.
- Place the paper card on the cup.
- Put one DRY hand on top of the card and invert the cup, over a
large container or sink, holding the card in place (make sure the hand holding the card is
dry).
- Take the hand that was holding the card slowly away.
QUESTIONS:
- Why does the card have to be stiff?
- Why do we have to make sure that the hand holding the card on
the cup is dry? What will a wet hand do?
- What is keeping the water in the inverted cup?
- Can we hold the cup slanted without letting the water pour out?
- Will we be able to do the same thing with other liquids?
(ie:
alcohol, oil, carbonated drink, etc.?)
RATIONALE: When the cup is completely filled
with water, there is no air left in the cup and thus no air pressure. The inverted cup can
therefore hold the water up, because the atmospheric pressure is working against the
under-side of the cup.
In the case of a partially filled cup of water, we can explain
it as follows: During the process of inverting, some of the water is dripping out, this
increases the volume of the air pocket without increasing the amount of air, thus
decreasing the pressure of the air pocket above the water. Again, the atmospheric pressure
is therefore larger and thus holding the water inside the cup.
Alcohol and oil will also be held up inside the inverted cup,
but the carbonated drink will not, because the carbon dioxide exerts pressure inside the
glass above the liquid and prevents a partial vacuum from forming.
Due to the adhesion of water to the card and the hand, a wet
hand could pull the card away from the top of the glass. The cup can be slanted as long as
no air is permitted to enter the glass.
APPLICATION: You can not drink a complete
bottle or can of pop without allowing air to enter the container. When you pour gas form a
gas can into the lawn mower, you must have an air vent or the gas splashes due to
intermittent air rushing into the nozzle to replace the area previously occupied by the
gas.
MATERIALS: An empty milk carton or tin can
PROCEDURE:
- Make three small holes in one of the sides near the bottom of
the milk carton -- about 1/2 cm away from each other.
- Fill the carton full with water and observe the water streams
coming out of the holes.
- Bring the streams together with the fingers to make it one big
stream. Seperate the streams by pushing one finger through the middle of the large stream.
QUESTIONS:
- Why does the water stay in one stream once they are brought
together?
- How far can the holes be placed apart for the water still to be
able to cling together?
- Is it easier to seperate (or bring together) the stream with a
full or almost empty carton?
EXPLANATION: The closer the holes are placed
in the carton, the easier to get a whole stream out ofthe carton, but the harder to
seperate it into three seperate streams. The farther the holes are, the harder to bring
the separate streams together. It is the cohesive forces between the water molecules that
keep the streams together. The fuller the carton, the larger the pressure, and the easier
the seperate streams are obtained. With less water in the carton, we will get lower water
pressure and thus an easier cohesive whole stream.
APPLICATION: We find this phenomenon in daily
life in the shower head with the many holes in it. When the valve is turned wide open,
separate streams are distinguished, but when the valve is only partially opened, the many
small streams will cling together and form one whole stream.
MATERIALS:
- 6 to 12 volt battery operated buzzer (Radio Shack 273-068)
- nine volt battery
PROCEDURE:
- ask for three volunteers from the class
- seat all three together in the center of the room; one facing
one end of the room, one facing the other end, and one facing at right angles to the ends.
- blindfold all three; they must sit still and not move their
heads. The rest of the class can form a circle around the room.
- turn on buzzer
- have two students throw the buzzer from one end of the room to
the other repeatedly several times. (The faster the buzzer is thrown, the better the
effect).
- have the volunteers indicate after each throw which direction
the buzzer was thrown.
- rotate volunteers so that each has an opportunity to listen from
all three positions.
QUESTIONS:
- what happens to the pitch as the buzzer approaches?
- what happens to the pitch as the buzzer moves away?
- when you are facing the approaching buzzer which sound is most
noticable?
- when you have your back to the approaching buzzer which sound is
most noticable?
- when you are at right angles to the passing buzzer which sounds
do you hear?
RATIONALE: The doppler effect is the perceived
change in frequency or pitch as the source of sound moves toward and away from us.
The sound we hear from the buzzer is produced by pressure on
air molecules to form waves. When the buzzer is in rapid motion there is an opposing
pressure in front which acts on both the buzzer and the sound waves. The result is that
there is a shorter distance between sound waves in front of the buzzer and therefore a
higher frequency. The same forces also act on the waves produced behind the buzzer,
tending to force them further apart, producing a lower frequency as the buzzer moves away.
This can be visualized by placing a short slinky on the table. Grasp the slinky in the
middle and push longitudinally. The force causes the distance between rings to become
shorter in front and longer behind.
The person facing the thrower will hear predominately the
rising pitch. The person whose back is to the thrower will hear predominately the drop in
pitch. The person sitting at right angles and the students around the room should hear
both, with a change from high to lower at the moment the buzzer passes.
If the students do not have any prior knowledge of the doppler
effect, the blindfolded students will soon loose track of the direction the buzzer is
moving. This will serve to demonstrate how both sight and bi-directional hearing are used
to determine the direction of sounds.
APPLICATION: train horn at railroad crossings;
race cars passing grandstands; cars passing by you while standing by the interstate.
MATERIALS:
- Two empty soft drink cans.
- About two dozen straight drinking straws.
PROCEDURE:
- Spread the straws parallel to each other on the table and leave
about 1/2 to 1 cm gap in between them.
- Place the two cans upright about 2 cm from each other on the
straws and show the students that they can easily move closer or further apart.
- Blow in between the two cans with a short hard puff.
- Now spread the two cans about 5 cm apart. Blow harder.
- Now place the cans about 20 cm apart. Take a deep breath and
blow a constant stream of air on the RIGHT SIDE of the LEFT can and move your head towards
the right, while constantly blowing.
QUESTIONS:
- What made the cans move towards each other?
- How far apart could the cans be placed and still be drawn
together?
- What does the flowing air create in between the cans?
- Was a stronger flow of air necessary to bring the cans that were
20 cm apart together?
RATIONALE: Blowing in between the cans created
a flow of air and thus a lower pressure compared to the stationary air on the other side
of the cans. It is this lower pressure that drew them together. Theoretically, the cans
could be placed an infinite distance away from each other and still be drawn together, as
long as a constant flow of air on one side of one can moves along with it, to move it to
the other can. Indeed, the faster the flow of air, the lower the pressure it exerts. But
for the cans that were placed 20 cm apart, only a constant flow that could move the can,
was necessary.
APPLICATION: Aviation (
ie. airplane wings)
MATERIALS:
- a hammer with a wooden handle
- a wooden yard stick, cut smoothly in half
- a short string or wire
- books
PROCEDURE:
- Before class, take one half of the flat wooden yard stick and
place on a table top with an overhang.
- Let the end of the yardstick extend from the edge of the table
top.
- Make a loop out of the string or wire (about 10 cm in diameter),
and slip it around the ruler and the handle of the hammer. Hang the hammer, with the iron
part of it down, by means of the string. Let the end of the handle press against the end
of the yard stick. The head of the hammer must be under the edge of the table top. Slowly
move the stick away from the edge of the table while at the same time moving the hammer
towards the table until just a few inches remain on the table top. The head of the hammer
must be directly below the end of the yardstick on the table.
- Place the other end of the yardstick end to end on the table so
that it appears to be complete.
- place books on top of the yard stick.
- After class starts, draw the students' attention to the hammer.
- Remove the books.
- Remove the free end of the yardstick.
QUESTIONS:
- What made the heavy hammer stay up at the edge of the table?
- Why do we need a hammer with a wooden handle?
- Can we consider the hammer suspended without support?
- Where is the center of gravity of the hammer alone?
- Where is the center of gravity of the whole system of ruler,
string and hammer?
- What is the difference between a stable and labile system?
EXPLANATION: This demonstration can only be
carried out when the hammer has a wooden handle, as the CENTER OF GRAVITY is located in
the iron part of the hammer. The yardstick and string do not add much to the weight of the
system on the handle side. They make the position of the center of gravity of the whole
system shift just a little towards the table and upwards. If this center of gravity is
under the pivot point (point of support), it is a stable system. If the center of gravity
is to he right or left of the pivot point, it is labile and it falls.
APPLICATION: our ability to bend over without
falling.
MATERIALS:
corrugated plastic tube
- swimming pool drain hose or vacuum cleaner hose
- 6 feet long, 4 cm diameter
PROCEDURE:
Experiment #1:
- holding the plastic tube in one hand at one end, swing it above
your head using only the wrist.
- swing slowly at first, then slowly increase the rate faster and
faster, then slow down again.
- try to vary the speeds to imitate the sound of a bugle
Experiment #2:
- tear a piece of paper up into small pieces
- place the pieces in a pile on the edge of a table.
- with one hand, hold one end of the tube just above the paper and
with the other hand swing the other end above your head.
QUESTIONS:
- How was the sound produced?
- How did the pitch change with increase in speed?
- Why did the pitch skip an interval each time it changed?
- What is the next higher pitch called?
- Which way is the air flowing in the tube?
- What caused the pieces of paper to move?
- Which experiment could be performed using a smooth walled tube?
Rationale:
This is an application of Bernoulli's principle. As the free
end of the tube passes through the air, the air pressure within the tube is reduced. Air
flows through the tube from the fixed end to the moving end. The papers move due to the
air moving into the fixed end of the tube.
As the air moves through the tube, it begins to oscillate due
to the corrugations of the tube. The corrugations determine the frequency of the
oscillations and thus the tone produced. At slower speeds the oscillations are slower
(lower frequency) and a basic low tone is heard. As the tube moves faster, the air moves
faster with the production of ovetones (harmonics). The next tone heard will be at a
frequency twice the original, or one octive higher, but only when the tube reaches a
certain velocity. No intermediate tones are heard at intermediate velocities. Higher
harmonic tones can be produced by increasing the rate of rotation. The sound will resemble
that of a bugle.
The quality of the tone is dependent upon the number of
corrugations per inch and the pitch dependent upon the length of the tube. Visit the
vacuum cleaner section of your local department store and try out several different tubes
to find one that you like.
APPLICATION: Pop Bottle Whistles; Oriental
flutes
MATERIALS:
- Two drinking straws.
- Three pins or needles and two pieces of thread
- Two identical uninflated balloons.
PROCEDURE:
- Tie a piece of thread to each of the two balloons and tie the
threads to the two ends of one of the straws.
- Balance this straw on your finger, push a pin through the straw
where it is balancing and attach it to the other straw held vertically.
- Make sure that the straws are moving freely around the needle;
balance the horizontal straw, then push a pin through at the spot where the threads are
attached (to prevent them from sliding).
- Make sure that the two uninflated balloons are in perfect
balance; then blow air in one of them and tie a knot in the mouth. The balance will tip
down at the end of the inflated balloon.
QUESTIONS:
- What is inside the uninflated balloons?
- What kind of air was blown in one of the balloons?
- What could happen if no pins were placed on the ends of the
horizontal straw where the threads were attached?
- What does the balance indicate after inflating one balloon?
- What would you expect the balance would do if the other baloon
was also inflated?
- How else could we show that air has weight?
RATIONALE:
The straw balance may be adjusted by moving the threads further
or closer to the end of the straw. In order to keep these attached threads from sliding,
we need the pins. The air that was blown in the balloon was exhaled air, which is
containing some water vapor but, for our purposes, may be neglected. By inflating the
other balloon, the balance should be in equilibrium again. The air in the balloon is
compressed by the balloon; therefore it is more dense and heavier than an equal volume of
air at regular atmospheric pressure.
APPLICATION: tanks of compressed gases
(ie. LP
gas)
MATERIALS:
- light weight string
- 2 to 3 kg weight with hooks on both ends
- roll of toilet paper
PROCEDURES:
Experiment #1
- suspend weight from top string with left hand
- pull on lower string with a quick pull with the right hand.
- replace
string(s) and repeat pulling with a slow steady
pressure.
Experiment #2
- hold or hang a roll of toilet paper in normal dispensing
position.
- pull on paper with a quick pull.
- pull on paper with a slow steady pressure.
QUESTIONS:
- Do you see any difference in the way the string was pulled?
- Why does a slow pull on the string break it above the weight?
- Why does a sharp jerk break the string below the weight?
- Which of the two breaks makes special use of the weight's
inertia?
RATIONALE:
By pulling the string slowly, we are putting a strain in the
string below and above the weight. Due to the mass of the weight, the strain above the
weight is much larger than below. The string snaps wherever the strain is highest.
When a sharp jerk is exerted on the string, the inertia of the
weight keeps the strain below the weight. Although there is some strain above the weight,
compared to the strain below the weight the strain in the latter is still higher, and the
string snaps below the weight.
APPLICATION: tow lines; tug of war
MATERIALS:
- solid wooden door
- piano wire (about 16 feet)
- 6 inch or larger turn buckle
- wooden block
(ie. 2 X 4, 4 inches long) for tone bridge.
- A 3/8 inch wood dowel, 12 to 18 inches long
- rosin
PROCEDURES:
- Place the piano wire around door lengthwise and join ends with
turn buckle on back. Protect the top and botton edges of door with small pieces of heavy
cardboard.
- Place block under wire approximately 1/4th the height of the
door above the floor.
- pull the wire as tightly as possible by hand and secure the
wire.
- stretch the wire by turning the turnbuckle until plucking the
wire 12 inches above the bridge produces a low tone.
- It should now resemble a large string bass (with only one
string).
- Starting near the top grasp the wire between the tips of the
thumb and forefinger of one hand and pluck the wire with the forefinger of the other hand.
Slowly move the thumb and forefinger down the wire until a sustained tone is heard. Place
a small mark on the wire at this point with a colored water proof marker. Repeat this
until all points have been identified. These are your node points.
DEMONSTRATION:
- Have several students, one at a time, try to produce sustained
tones while plucking the string with one hand 12 inches above the block and grasping the
wire with the thumb and forefinger of the other hand.
- rub the wooden dowel with rosin.
- Using the same points discovered above, draw the wooden dowel
across the string twelve inches above the block.
QUESTIONS:
- Why does the wire give different tones?
- What determines the pitch produced?
- Which spots give the highest pitch? the lowest pitch?
- What is heard if the wire is not grasp exactly at the specific
spots? Why?
- Is there a difference in sound when the rosin coated dowel is
used? Why?
- What would happen if a piece of cardboard was placed between the
wooden block and the door?
RATIONALE:
When the wire is plucked, transverse waves are set up in the
wire. When specific points are grasp, standing waves are formed which produce a sustained
tone. As you grasp points closer to the bridge, the vibrating wire is shorter, it vibrates
faster, and the pitch is higher. The higher frequencies are multiples of the lower.
Grasping of points other than the exact nodal points cancels out the standing waves.
Stroking the wire with the rosin coated dowel sets up
longitudinal waves in the wire. The wave lengths produced are the same and therefore the
same nodal points produce sustained resonating tones of the same frequency/pitch. However,
they are softer and more mellow in sound. This is why the string bass player sometimes
plucks the strings and other times uses a bow.
If a piece of cardboard or other absorbant material is placed
between the bridge and the door, very little sound would be heard. The door serves as a
sounding board which amplifies the sound waves produced by the string.
APPLICATIONS: String instruments,
MATERIALS:
- one/quarter inch diameter solid aluminum rod about one meter (3
feet) long
- hard object (small mallet, golf ball, etc)
- marking pencil
PROCEDURE:
- holding the rod between the thumb and forefinger, balance the
rod to find the center point.
- holding the center point between the thumb and forefinger, hit
the rod just below this point with a hard object. If a pure resonating tone is not
produced, move the thumb and forefinger up or down a short distance and repeat. Do not
hold the rod too tightly.
- place marks on the pipe at 13, 25, 35, and 39 cm on each side
away from the center. Holding the rod vertically at each of these points, check each point
for resonating tones. Make adjustments as necessary.
DEMONSTRATION:
- Hold the rod vertically between the thumb and forefinger.
Starting at the center mark, strike the rod with the hard object just below the center
mark.
- Repeat while holding at each of the other marks, striking the
the rod just below the center mark.
- Repeat while holding one centimeter away from each mark.
QUESTIONS:
- What tones do you hear?
- Why does the rod give different tones?
- Does holding the rod at different spots determine the pitch?
- Does the vibration continue if the rod is held at two spots at
one time? three spots at a time? Which of the spots?
- Which spots give the same tones?
- Which spots on the rod give the highest pitch? The lowest?
- What is heard when the rod is not held exactly at the specific
spots? Why?
RATIONALE:
Striking the rod sets up vibrations in the rod. When held at
specific spots, transverse standing waves are created which produce pure resonating tones.
The tone/pitch produced depends upon the spots where the pipe is held. The spot 25 cm away
from the center gives the lowest pitch, whereas the spots 13 and 39 cm from the center
gives the highest pitch due to the shorter wavelength produced. The nodes of the standing
waves are located at these specific spots on the rod. When the rod is held at points away
from these spots, antinodes are created and the waves interfere or are cancelled out.
APPLICATION: Musical triangles; musical chimes
MATERIALS:
- PVC drain pipe, 1.5 to 2 inches diameter, several lengths from
two to five feet long.
- Propane torch.
PROCEDURE:
- light propane torch and turn on to largest (hottest) setting.
- hold the torch in a position so that the flame is perpendicular.
- lower pipe vertically over flame. Adjust height until tone
developes.
- repeat with each length of pipe.
QUESTIONS:
- How is the tone produced?
- Is there a difference in pitch with different lengths of pipe?
RATIONALE:
The heat of the flame causes the air in the tube to suddenly
expand. The hot air begins to oscillate up the tube, resulting in a resonating tone. A
standing wave is created in a tube with open ends. The longer the tube, the longer
wavelengths are produced in the standing wave and thus the lower the tone.
APPLICATION: steam whistle; upward air draft
on a chimney
MATERIALS:
- A dry glass or transparent plastic cup
- A large beaker or transparent plastic container large enough to
fit a person's hand into.
PROCEDURE:
- Fill the large container about 2/3 full with water.
- Crumple a piece of dry paper and squeeze it to the bottom of the
glass or plastic cup.
- Invert the glass (making s;ure that the crumpled paper stays up
in the cup) and immerse it completely under water, holding it as vertically as possible.
- Take the cup back out ofthe water and let the water drip off (do
not shake off)
- Take the crumpled paper out of the cup with a dry hand and let
the students feel and check whether it is dry or not.
QUESTIONS:
- What is in the cup?
- What else besides the paper is in the cup?
- Why doesn't the water enter the cup?
- Why does the paper have to be crumpled?
RATIONALE:
Air is space occupying. The glass is filled with air, no matter
whether it is right side up or upside down. Besides the crumpled paper there was air in
the cup. This is why the water could not enter the cup during the immersion process.
Therefore the paper stayed completely dry.
APPLICATION: This characteristic of air can be
found when people have to work under water. Air is pumped in and around the area where the
people are working, enclosed by a water-tight wall.
MATERIALS:
- plastic drinking straws
- pair of scissors
PROCEDURE:
- flatten one end of the straw.
- cut triangle pieces off both sides of the end to form tapered
reeds.
- place reed end in your mouth with reeds inside lips.
- blow to obtain an oboe sound.
- the straw may need to be shifted in or out slightly. Also reeds
may need to be flattened together. This may be done by biting with the front teeth.
- the pitch can be adjusted by cutting small pieces off the open
end.
- adjust each straw to a different note of the musical scale. Try
combining different pitches to form pleasing sounds.
QUESTIONS:
- What is actually producing the sound? How?
- What change in pitch do you get when you cut off a piece of the
end?
- What does changing the length mean in terms of vibrating air
column?
RATIONALE:
By cutting the end of the straw, we made two reed-like
protrusions. When air is blown through them, they will vibrate and set up vibrations in
the air. The pitch heard is determined by the length of vibrating air. By shortening the
length of the straw, the column of vibrating air is shorter and the higher the pitch.
APPLICATION: reed musical instruments
MATERIALS:
- one empty aluminum pop can (354 ml)
- a hot plate or burner
- large bowl of water
- tongs to hold the pop can
PROCEDURE:
- put about 5 ml of water in the pop can (just enough to cover the
bottom).
- heat the can over the hot plate or burner
- let the water boil vigorously, it won't take long
- in a single motion, remove the pop can from the burner and
INVERT it in the bowl of water.
- submerge the opening to the pop can into the water. The can will
implode instantly.
QUESTIONS:
- What was in the can besides the water?
- What happens when water is boiled?
- What do you think will happen if the can is inverted in the bowl
of water?
- What happens to the air in the can as water vapor is formed?
- What force is working on the outside of the can?
RATIONALE: Before heating, the can was filled
with water and air. By boiling the water, it changed states, from liquid to gaseous state
(water vapor). The water vapor (steam) pushed the air that was inside, out of the can. By
inverting the can in water, we are cooling the vapor very quickly and constraining the
potential for rapid flow of air back into the can by submerging the top in water. The
cooling condenses the water vapor back to water. All of the vapor which took up the
interior space of the can before is now turned into a few drops of water, which takes up
much less space. This causes the pressure to drop and the atmospheric pressure is
therefore pushing on the can and crushing it.
The total force working on the outside of the can is the total
of the can's surface area in cm multiplied by 1 Kg.
APPLICATION: production of vacuum containers,
Home canning
MATERIALS:
- a pencil
- a piece of molding clay.
PROCEDURE:
- Place the pencil vertically in a piece of clay on the table top.
- let the students one by one try the following, while the rest of
the class observes:
Approach the pencil from the side about 3 to 4 meters away with
one eye (cover the other eye with your hand). Hold the other hand stretched out and
without hesitation, point down with the index finger and try to touch the pencil. Repeat
again. Now repeat with both eyes open.
QUESTIONS:
- Why did most students miss touching the pencil end?
- After a student tried to do the trick several times, why did
he/she get better at touching the pencil?
- Do you think it would be easier to do by approaching the pencil
slowly?
- What happens when the experiment is done with both eyes open?
- What do you lack when just one eye is used?
- Why must the pencil be touched without hesitation?
- If we see differently with each eye, why don't we see two images
when both eyes are open?
RATIONALE: Most people will not be able to
touch the pencil on the first try. They can not see with one eye how far in front of them
the pencil is located. One cannot judge depth and distance as well with one eye as with
two. With one eye, one sees everything in the same plane (as in a picture). In other
words, everything becomes two dimensional rather than three dimensional. We see in three
dimensions with both eyes because the brain assimiltes into one frame of reference the
different perspectives of the images received from the eyes.
APPLICATION: depth perception for driving;
jobs requiring hand- eye coordination. With a little practice one will get better at
judging distances with only one eye.
MATERIALS:
- Two blank sheets of white paper.
- a pencil
PROCEDURES:
- Make a hole in the center of one sheet of paper with a pencil.
- Draw a black dot in the center of the other sheet of paper the
size of a penny, and place this about 40 cm in front of you on the table.
- With both eyes open, hold the sheet with the hole between your
face and the sheet with the dot, and move the sheet about until the black dot can be seen
through the hole.
- While holding this sheet steady (while seeing the dot), close
first your left eye and then your right. When does the dot disappear?
QUESTIONS:
- Does the dot disappear after closing you left or right eye?
- If the dot disappears when closing your left eye, are you left
sighted or right sighted?
- If the dot disappears when closing your right eye, are you left
sighted or right sighted?
- After determining that you are right sighted, does it make any
difference whether you are closing your left eye or not in looking at the dot?
EXPLANATION:
For most people, the dot will disappear when closing the right
eye. This indicates that most people are right sighted. It means that most people prefer
to use their right eye over the left, if they are confronted with the option of using only
one. In this case it means that those people can see the dot with both eyes open or with
only the right eye open, but not with only the left eye. In other words, when both eyes
are open, the left eye does no work. There is probably a connection between this
phenomenon and the right handedness of most people, although it would be hard to say which
is the cause and which is the effect.
APPLICATION: looking through a monocular
microscope or telescope.
MATERIALS:
- A plant with large wide leaves and long stems
(ie. )
- two small erlenmeyer flasks.
- two 2-hole stoppers that fit in the flasks.
- two short glass tubes bent in shape of an "L".
- a candle and matches
PROCEDURE:
- The night before the demonstration, place plant under a grow
light. Cover one leaf with paper bag. (cover one leaf for each demo per day)
- Clip the light exposed and covered leaves at the base of the
stem.
- In their respective flasks, stick the leaf stem through one of
the holes in the 2- hole stopper almost to the bottom of the flask. Seal it with dripping
wax from a lit candle.
- Insert the bent glass tubes in the other hole of the stoppers
just to below the stopper.
- Fill the Erlenmeyer flasks with water to such a level that only
the leaf stems are immersed in it and not the glass tube.
- Place the stoppers tightly into the flasks. Uncover the leaf.
Suck through the side tubes.
QUESTIONS:
- Why do the stems have to be sealed in the stoppers?
- What would happen if the glass tubes were also immersed in the
water?
- What do you observe issuing from the end of the stalk of the
light exposed leaf but not from the covered leaf?
- What is the source of this gas? What is the gas?
- What are the properties of the light exposed leaf and stem that
allows gas to exit?
- Why does the gas not come from the leaf kept in the dark?
- What is the structure of leaves that regulates the flow of air?
- How is this structure different in the leaf kept in the dark?
RATIONALE:
The sucking through the side tube lowered the pressure inside
the flask, causing the atmospheric air to seep through the leaf and the stalk resulting in
the bubbles issuing from the end of the stalk. When examined under the microscope, the
underside of the leaf contains pores (stomata) with two little guard cells on each side of
the opening. These guard cells regulate the opening and closing of the stomata in response
to light. Note that the stomata are open in the light exposed leaf and closed in the leaf
kept in the dark. Alternatively to covering the leaf is to spray the leaf with salt water
to force the guard cells to close the stomata.
Application: plant growth
MATERIALS:
- Three empty
soft drink cans.
- Two
styrofoam cups
- Lighter
fluid
- A match.
- Goggles
PROCEDURE:
- With a can
opener, cut open the ends of the cans as follows:
Top can: open on top, only half of bottom removed.
Middle can: open on both ends.
Bottom can: only half of top removed, leave bottom closed.
- Connect the
three cans on top of each other with masking tape or duct tape.
- Punch a
hole about 2 cm from the bottom, in the side of the bottom can and about one
half cm in diameter (ie. use a large nail)
- Tape the
two styrofoam cups together rim to rim, and place it tightly in the top
opening.
- Place two
or three squirts of lighter fluid in the bottom hole and shake the stack of
cans.
- Let stand
for a few seconds. You are now ready for ignition!
- Strike a
match and hold the flame close to the bottom opening.
- 8. BE
CAREFUL, KEEP AWAY FROM THE CANNON BALL!!
QUESTIONS:
- What are
the two baffles in the cans for?
- What
purpose did shaking the stack of cans have?
- What kind
of energy resulted from the chemical explosion?
- What other
kinds of liquids do you think could be used in place of the lighter fluid?
RATIONALE: The
baffles were left in the cans to enhance the mixing of the fuel with the air in
the cylinder. The baffles momentarily retain and reflect the heat of ignition to
ensure complete combustion of all of the fuel. The shaking of the cylinder was
also done immediately after the fuel was injected for exactly the same reason.
The better the mixture of fuel vapors and the air, the better the explosion. The
chemical energy stored in the lighter fluid is transformed by the combustion
into kinetic energy of the moving cannon ball. Gasoline or alcohol may be used
instead of lighter fluid.
APPLICATION: internal combustion engine;
liquid fuel rockets
MATERIALS:
- grapes, peeled and unpeeled
- carbonated water (soft drink or alka seltzer tablets)
- a clear drinking glass
PROCEDURE:
- fill the glass with carbonated water (or one alka seltzer tablet
per glass of water)
- drop the grapes, one peeled and one unpeeled, into the glass.
- observe what happens.
QUESTIONS:
- what property does the peeled grape have or lack?
- what property does the whole grape have or lack?
- why does the water have to be carbonated?
RATIONALE:
If the peeled and unpeeled grape were examined after washing in
plain water, you would see that the peeled grape looks and feels wet all over. But the
whole grape will feel and appear beaded with water. This property of the skin of the grape
is hydrophobic or water repelling. In the carbonated water, the carbon dioxide bubbles use
this property to collect around the grape. This results in the grape having greater
bouyancy and the grape floats. With the loss of this property by the peeled grape, it does
not float.
APPLICATION: proteins in cell membranes which
selectively allow passage of materials into and out of the cytoplasm.
MATERIALS:
- about 100 ml of sugar crystals.
- two 100 ml beakers
- two glass stirrers
- concentrated sulfuric acid (USE CAUTION)
PROCEDURE:
- fill each beaker half full with sugar.
- add about 40 ml of water to the first beaker and the same amount
of concentrated sulfuric acid to the second beaker.
- stir and let stand.
- observe the difference between the two changes in the sugar.
- the reaction should preferably be carried out under a fume hood
or close to an open window, or in the outdoors.
QUESTIONS:
- What is the difference between the processes in the first and
second beakers?
- How can we recognize or distinguish between a physical change
and a chemical change?
- In which beaker do the reactants still have the same properties?
- In which of the two beakers could we get the sugar back as
sugar?
- What do you think happened in the second beaker?
- What property do you think concentrated sulfuric acid has?
- What do you think the black material is in the second beaker?
RATIONALE:
In the first beaker where the sugar was mixed with the water, a
physical change was taking place. This means that the components of the mixture retained
their properties; they could be separated and still have the exact properties as before
the change. The water could be left to evaporate and the sugar would crystalize out of the
solution.
In the second beaker a chemical change took place. The products
formed have properties that are completely different from the original components of the
mixture. A black charcoal mass is produced, which is expanding up because of the gases
(sulfur dioxide) and water vapor being released. This is caused by the dehydrating
properties of concentrated sulfuric acid.
APPLICATIONS: cooking and baking; digestion of
foods in the body
MATERIALS:
- Thick rubber bands
- Meter stick
- Sufficient weight to stretch the rubber band 2 cm
- Small flame
PROCEDURE: (Exp. #1 and #2 to be done by class
together)
Experiment #1
- place the rubberband on your lower lip and make a mental note of
the temperature.
- holding the rubberband looped over both index fingers, quickly
stretch it to almost its maximum length (do not break) and hold.
- immediately place the stretched rubberband to the lower lip to
check temperature.
- for improved effect, rapidly stretch and release five times, the
last time keeping it stretched and place on the lip.
Experiment #2
- repeat step #2 from experiment #1, excepts keep it stretched for
at least ten seconds.
- allow the rubberband to quickly return to its original length.
- immediately touch it to your bottom lip.
- repeat at least twice.
Experiment #3 (done as a single demonstration)
- fasten one end of the rubberband to one end of an upright meter
stick.
- suspend the weight from the other end of the
rubberband. Note
the mark where the weight hangs.
- place the flame near the
rubberband.
QUESTIONS:
- What change in temperature did you note?
- What caused the temperature change in experiment #1? In
experiment #2?
- What happens to the rubberband and weight when external heat is
applied?
RATIONALE:
Whenever there is a rearrangement of atoms from one molecule to
another energy is transformed. Part of this transformation is expressed in the production
or absorption of heat. In experiment #1 you supply the energy required to rearrange the
atoms making up the molecules of the rubberband. The rapid rearrangement causes atoms to
collide, giving up energy in the form of heat (exothermic). Based on the conservation of
energy, when an exothermic reaction is reversed, heat must be put into the reaction
(endothermic).
In experiment #2, in order for the atoms to resume their
original tight arrangement in the molecules of the rubberband, energy transformation in
the form of absorbed heat must occur. A body in the process of absorbing heat will feel
cool. Since contraction in the molecular structure of the rubberband is an endothermic
reaction, in experiment #3 the application of heat produces contraction.
APPLICATION: tires on moving vehicle, energy
production in cells, chemical reactions.
MATERIALS:
- Plastic or glass bottle with medium sized neck (Gator Aid Bottle
or 500 ml Erlenmeyer Flask)
- 12 to 18 inch long heavy walled rubber or plastic tubing or
stiff rope, no more than half the diameter of the neck of the bottle.
- small balloon
PROCEDURE:
- If the bottle is not opaque, cover with tin foil from top to
bottom.
- place the balloon in neck, inflate until it forms a small ball
in the neck, and tie the end (proper siz of balloon is critical)
- push balloon into bottle.
- place tubing into bottle, invert bottle, and gently pull on
tubing.
- the bottle can now be suspended by holding onto only the tubing.
DEMONSTRATION:
- present the bottle and tubing
seperately.
- explain that this is a demonstration on scientific observation
and proposing a hypothesis based on observation.
- place hose in bottle, invert to lock in balloon.
- allow bottle to suspend from tubing.
- holding bottle in one hand and pushing in on tubing slightly,
remove tubing.
- repeat procedure while discussing principles of scientific
observation and forming hypothesis.
- you can invert the bottle and shake the bottle, but do not
permit handling by students.
QUESTIONS:
- What is scientific observation?
- Why does scientific observation not always include close
inspection?
- What is a hypothesis?
- Based on the observations made, what is your hypothesis of how
the tube and bottle interact?
RATIONALE:
Scientific observation consists of making note of all details
relevant to the object or situation being observed. The area of study dictates the types
of relevant details. Some objects can be observed through inspection, however many objects
of scientific study are too large, too small, or too far away (ie. rock formations,
microorganisms, planets, etc.) for hands on inspection. A hypothesis to explain the
operating principles is based on assumptions, interpretations, and inferences based on the
observations made.
APPLICATION: Scientific observation
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