ingridscience

Hand out stacks of paper to each student.
Ask them to build a tower as high as they can with their paper. They can fold and tear the paper as they wish, but get no more materials.
Encourage them to exchange ideas (as adult engineers do the same).
Point out the different styles of towers, and the various ways that students reinforce their structure to make it stable e.g. rolling sheets to make strong columns, creating stability by leaning sheets against each other etc.

Before the activity, tie the end of each string to the elastic band, to make a ring of strings extending outwards.

Place the cups downwards on the floor and spaced apart.
Hand each student the end of each string, and ask them to space out so that they can open and close the elastic band by collaboratively pulling on their strings.
Ask them to use the elastic band and string contraption to arrange the cups into a tower with a two-cup base with one on top.
They may need to be reminded to stay at the end of their strings.

Students need to work closely together, to discuss who should pull or loosen their string, in order to pick up each cup and place it. Placing the top cup will be hardest and they may try several times. They may drop a cup on its side, and will need to figure out how to right it together.

Encourage respectful teamwork, and that no idea is a bad idea.

Gather 30m or further from a flat wall, and demonstrate by a single loud clap, or one bang of the wooden blocks together, that there is an echo. The sound of the clap/blocks, reaches the wall and bounces back to us, so that there is a delay between the initial sound made and the sound heard after it bounces off the wall.

Discussion on echolocation:
Some animals (e.g. bat) are able to use the echo to measure how far away prey is, as well as the size and shape of objects to navigate in a dark cave.
Some blind people use echolocation, by clicking their tongues and listening for the echo back to find out where objects are (just like bats or marine animals). Some blind people can so precisely tell where objects are using echolocation that they can use this method for mountain biking or basketball! https://www.youtube.com/watch?v=WHYCs8xtzUI Experts in blind echolocation can even listen to a recording of tongue clicks echoing, and state what objects were there when the recording was made!

To measure the speed of sound:
By timing how long the delay is and measuring how far away the wall is, we can measure how fast sound travels.
This works best with a longer distance of 40 or 50m from the wall.

Show students how long a metre is using the tape measure, then ask them to see how long their stride must be to measure a metre. Once their stride is calibrated to a meter, ask them to pace out the number of strides (or metres) to the wall.
Write down this number [52m and 58m for two of our students]. Double the number to find out how far the sound must travel to the wall and back [110m for us].

Meanwhile, another student needs to bang the wood blocks together so that the echo from the first bang coincides with the echo from the second bang. Ask them to keep banging the wood at this rate, so each bang coincides with the echo from the previous bang. The time between the bangs is the time it takes the sound to travel to the wall and back.
To be somewhat accurate in how long it takes the sound to travel the distance, ask the student to keep banging the blocks together at the same rate, while another students times 10 bangs of the blocks. [Our students measured 3.42 seconds for 10 bangs.]
Divide this number by 10 to find the time for one bang i.e. the time for sound to travel to the wall and back [0.342 seconds for us].

Now do some math: if the sound travels x metres to the wall and back, and takes y seconds, the sound is travelling at x/y metres in one second - this is the calculated speed of sound. [We calculated 110/0.342 = 321.6 metres per second, approximated to 320m/sec.]

The actual speed of sound in air is 343m/sec, so this method is not bad for calculating the speed of sound.

Make a hole in the centre of two cup bottoms.
Push one end of the string through a hole in a cup, then tie a knot on the inside of the cup so that the string is secure. Repeat with the other end of the string and the other cup.
Pairs of students each hold a cup, and move apart until the string is taught. They can then communicate by talking into one cup and putting the other over an ear. The sound is pretty decent, as long as the string is taught.

Discuss how the sound is transmitted: the cup catches the sound and transmits it to the string. Sound is a vibration of molecules, so the vibration of the air molecules in the cup causes molecules in the string to vibrate. The vibrations transmit along the string to the other cup, where they cause vibrations in the air of the second cup. This moving air reaches the ear, where the vibrations are transmitted into the ear, where they are converted to electrical signals that are passed to the brain along nerves.

Optional: do not tell the students that the string needs to be taught and allow them to investigate how the telephone works best, with slack or taught string.
Optional: experiment with different string diameters and different cup sizes and different string lengths.
Optional: play the telephone game, by making a circle of students and string telephones between them: one student passes a message down a string telephone to the next student, who uses the next telephone to pass the message they hear on to the next student, continue until all the students have received and passed on the message, until the last student tells the group what they heard (similar to the game where the message is whispered between participants). See how garbled a message becomes from the first student to the last - discuss why: the string telephones are not perfect at transmitting sound, and so some words are hard to make out.

Discuss what sound is: molecules vibrating back and forth, which bump the next door molecules, passing the vibration through the air (or liquid or solid). When those molecule vibrations reach your ear, they cause your eardrum to vibrate, which transmits all the way to your inner ear, where tiny hairs move. The moving hairs initiate an electrical signal which gets sent via nerves to the auditory section of your brain. Only then do you perceive the sound.

How low or high a note is depends on the frequency (or speed) of the vibrations. Faster vibrations sound higher, and slower vibrations sound lower. The rate of the vibrations are measured in Hertz, or Hz.

Tell students that different people can hear different frequencies - some can hear higher than others, and some can hear lower. This activity collects data on the frequencies that students and adults can hear.
Demonstrate what kind of sound they will be hearing, by turning on the tone generator and the connected speaker, and running up and down the frequencies.

Start data collection. Start the frequency generator at the highest, slowly lower the frequency, and ask students to put their hand up when they start to hear the tone. If at any point, it is hurting students' ears, lower the volume (it may hurt students while adults cannot hear it at all).
When students raise their hands, write down the frequency you are at, and ask students to do the same (see photos). Keep lowering the frequency, and keep writing frequencies down, until all present in the class can hear the tone. (It is good to start high, so that students are less likely to feel inadequate at not hearing the tone - adults will likely be the last to hear.)

Then collect data on the lowest frequency humans can hear. Continue to lower the frequency and ask students to raise their hands when they no longer hear it. Note that the tone may get very quiet, so be sure to raise the volume on the phone and speaker, and if necessary, move the speaker around the classroom sot that students can put their ear to it. Record the lowest frequencies perceived on the board. (Note that the limits of the speaker may define the lowest note that can be played.)

Discuss the results. There is a range of frequencies that students can hear, due to variability in their ear physiology. Show students a diagram of the inside of the ear and the path that the sound takes, to show the complexity of sound perception. The ear drum is vibrated by sound in the air, which transmits these vibrations through the bones of the middle ear to the liquid in the cochlea canal of the inner ear. When the hairs in the cochlea vibrate, they generate an electrical signal that neurons transmit to the brain - only then do we perceive the sound. Adults are usually unable to hear the higher frequencies that students can hear, as during aging humans lose the inner ear hair cells that are sensitive to high frequencies.

Compare to other animals. Show students a diagram of animals’ hearing range compared to humans. Humans are able to hear frequencies ranging from 19,000Hz (19KHz) down to 30Hz. Bats can hear higher frequencies than humans (called ultrasound), up to 115KHz, and use these frequencies for echolocation. Elephants can hear lower frequencies than humans (infrasound), down to 17Hz.
Try these webpages with animal frequency ranges: https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Animal_hearin… http://www.philtulga.com/AnimalHz.gif http://elephant.elehost.com/About_Elephants/Senses/Hearing/infrasounddi…

Grow the brine shrimp for the lesson:
Start growing the shrimp two or three days before the lesson. Prepare 2% sea salt in dechlorinated tap water (i.e. 2g salt in 100ml water or equivalent - I use 20g in a litre of aged tap water), enough to fill the plastic box to a depth of 3-5cm. Sprinkle brine shrimp eggs over the surface, to make a sparse coating. Leave in a space with natural light, undisturbed. (Some sources say to add a bubbler to the water, to provide more oxygen, but for my use I have found that this is not necessary, though my hatch rate is likely lower.)
The shrimp should hatch after a day or two, and can be left another day or maybe two before using for the activity (I wait 2.5 days after adding the eggs to the salt water, before harvesting) After too many days without food or water replacement, that remove ammonia and other toxins, the young shrimp (called nauplii, singular: nauplius) will start to die.
To harvest the shrimp for the lesson, place near a bright window, with one corner of the box facing the window. If a window is not bright enough, point a flashlight at the corner of the box. Raise up the end of the box facing the light with a book.
The shrimp will move towards the light, so wait a few minutes, then use the pipette to suck up a concentration of shrimp in the shallower water nearest to the window. Transfer to a small jar or other container to bring to the lesson. Avoid the empty egg cases floating on the surface of the water.

Observing brine shrimp closely:
At the start of the lesson transfer about 100 shrimp to each blacked-out petri dish. Ideally have one dish per pair of students.
Hand out one flashlight for each dish, and ask the students to keep the lid off, and use the flashlight to find the shrimp in their dish. Show them by scanning the flashlight over the dish at an angle, the shrimp can be found more easily. Ask students to watch the movement of the shrimp - they will move along in a jerky way, following a zig-zag path.
This is a good time to use a higher power microscope to look at a shrimp closely. Ideally project the image on a screen so that the parts of the shrimp can be discussed together more easily. The juvenile shrimp use their antennae as paddles to push (or "row") through the water, hence the jerky movement. As they get older they will grow legs and swim with a smoother motion. The juvenile has one eye at the front of the head. They will later grow a pair of eyes, located on the sides of the head.
The juvenile will initially eat the yolk remaining from the egg it was born from, then start to feed on tiny algae in the water.
Brine shrimp are found naturally in salt water, such as the Great Salt Lake in Utah, the Caspian Sea, inland salt swamps, as well as in coastal waters near San Fransisco. They need salt water, but can live in salt concentrations as low as sea water (about 3%) or as high as 50%!

Light attraction of brine shrimp:
While looking closely at the shrimp, some students may have noticed that they are attracted to the light. ("Phototaxis" is the term for movement in response to light, and attraction to light is called positive phototaxis.) This observation introduces the activity.
Ask all students to observe the attraction of shrimp to (white) light using these steps:
1. Gently swirl the dish to distribute the shrimp evenly, then carefully place the lid on.
2. Hold or rest the flashlight over the open corner of the lid, and wait one minute, without disturbing the dish.
3. Carefully lift the lid, without jostling the dish, and immediately look to see where the shrimp are distributed. Quickly scan the flashlight over the dish to find the location of all the shrimp.
Most of the shrimp will be gathered under the location of the light. Not all of the shrimp will have moved there though. This distribution of shrimp is called a "strong attraction" to light. (See photo of instructions and shrimp distribution images.)
Discuss why the shrimp might be attracted to the light: they eat algae, which are near the surface of the water where there is more light. (The algae need light for photosynthesis so they collect where there is more light.)

Explain that different colours of light attract shrimp differently, and that the students will find out which colours shrimp are more attracted to.
Hand out the filters.
Ask students to repeat the steps as for the white light (1. swirl dish, 2. light over dish, 3. look at distribution), but with filters between the dish and the light, so that the shrimp are exposed to different colours.
(We used two of each filter colour, which I had previously determined to give best results i.e. for blue light, use two blue filters, for red light use two red filters, for green light use one blue and one yellow filter etc.)
Make sure that all students try blue, red and green light, then they can mix pairs of filters to try any other light combinations they wish. Students use a worksheet to record whether the shrimp are "strongly attracted", "weakly attracted" or "not attracted" to each light colour.

The students should find that the shrimp are strongly attracted to blue light, and not attracted (or weakly attracted) to red light. We found that shrimp are also strongly attracted to green and purple light. We did not have enough data points to graph yellow and orange light.
See the data photo for our results (S indicates strong attraction, W indicates weak attraction, - indicates no attraction, with the number of dishes reporting for each). See the graph for our results of those colours with 11 or 12 dishes reporting. With more time, more groups can try all the colours.

Discussion of possible reasons for attraction to certain light colours.
Allow students to speculate as to why brine shrimp might be more attracted to certain colours. Encourage thought around what might help these animals survive (e.g. food, habitat etc). Encourage them to come up with other experiments to try (and a hypothesis to test) to find out.
During discussion, inject some ideas:
1. The food source of brine shrimp is blue-green algae - it might be advantageous to be sensitive to the colour of a food source, and to swim towards it.
2. The attraction to certain light colours correlates with how deep different colours penetrate water
e.g. https://i.pinimg.com/736x/0c/c0/50/0cc050beb2c576415fd0ab7238b7e4c9.jpg
e.g. http://oceanexplorer.noaa.gov/explorations/04deepscope/background/deepl…
Our shrimp were also strongly attracted to green and purple light, which penetrate fairly deeply into water, though not as deep as blue light.
Could shrimp have an adaptation that allows them to follow blue light to the surface of the water (where their food lives?)
(Note: I have not found much scientific research on light colour attraction specifically by brine shrimp, though there are many papers on light attraction by collections of small ocean animals, and how attraction varies with time of day, season, age of the animal, and wavelength of light - this is very current research that the students are doing their own experiment alongside.)

Other discussion points, if results are not aligned with the penetration depths of different light colours:
The filters being used are not passing a narrow band of light colours, but let other wavelengths through (I doubled up my filters to tighten up the data).
By adding filters, the intensity of the light is also reduced, which shrimp may also be sensitive to.
The wavelengths given off by the flashlight will also likely change the data. (I used a cool-white LED flashlight.)

Super interesting aside: as red light does not penetrate deeply into the ocean, deep ocean animals are red-coloured, so that they are camouflaged in the blue light of the deep ocean.
e.g. https://oceanexplorer.noaa.gov/facts/animal-color.html
Look at this image through a blue filter, and see the red animals of the deep ocean disappear!

Light attraction of other pond organisms
Other pond organisms show light attraction to white light (I have not tried other colours). Collect a dense population with a fine net to test.
Use the same set up indoors as for shrimp. Outdoors, the light of the sun can be used: collect pond life in a blacked-out dish, and place it on the ground in bright light. Leave the lid on for a few minutes, then remove the lid and immediately look for the distribution of the animals - they will be under the portion of the lid that was open to the light (see last photo). Just like the brine shrimp, they are attracted to light ("positive phototaxis").

Note this activity several days and up to two weeks.

Set up

Breads:
Students can choose what conditions they would like to test for how they affect the decomposition of bread. They should set up a series of samples, and record the treatments on a worksheet. Make sure that students understand that they should only change one variable at a time to conclude how a variable affects decomposition. If several groups are setting up the experiment, groups can pool their data as long as they are fairly consistent in how they handle the samples while setting up the experiments.
Examples of variables to try:

Drinks:
Students should add one of each kind of drink to a petri dish, for example:

• milk
• refrigerated apple juice
• sprite or other light-coloured soda

They can also choose one of the liquids and change another variable e.g. temperature, light level.
Make sure the drink samples have lids, or the liquid will evaporate away during the experiment.

Allow decomposition to occur
Leave the bread and drinks undisturbed for a week, then ask students to document any changes on the worksheet. They should notice changes in texture, colour and smell.
For safe smelling of a sample that might have unpleasant odours, teach students how to waft air from above a sample towards their nose (rather than sniffing the sample directly). If they find mould, they can record the number and colour of the colonies. They should leave the samples in their baggie/keep the petri dish lid on, to avoid possibly unsafe ingestion of mould spores.
Expected results:
After a week for the drinks, the milk will be clumped and stinky (discard it after the lesson), the apple juice may have a mould colony on it or not, the soda will be unchanged (except for gas that has come out of solution).
After a week for the breads, the bread with the shorter expiry dates will be starting to grow mould, especially if sprayed with water. Students can count the number of mould colonies. Make sure the students look for small colonies and under the bread too. The bread with a 10 day expiry date will be unchanged.

If there has been a lot of mould growth, likely because of higher classroom temperatures, maybe move to discussion of results and mould observation. If the mould colonies are small (1cm diameter or less), an additional week of growth is recommended to grow more impressive colours and colony sizes.

Discuss results
After final documentation of changes observed, discuss the class results in terms of conditions that living things that promote decomposition thrive in. A consolidated table of class results can help with discussion, though it can be complex with the many possible variables. If results across groups are compared, be sure to compare results with only one variable changed between them.

Drinks:
The soda likely did not encourage any mould growth. Read out the soda ingredients, and point out that it does not contain many nutrients (apart from sugar) that mould needs for growth.
Fresh apple juice likely had some mould growth, and the ingredients of apple pulp contain many nutrients as well as sugar, that mould needs for growth. Boxed apple juice that is sold at room temperature may yield different results.
Milk was clumped and stinky very fast. Discuss the microorganisms present in milk (mostly harmless bacteria) and that at room temperature, they have grown and multiplied. Specifically, the harmless bacteria Lactobacillus is present in milk (it is not destroyed by pasteurization), and as it grows it releases (lactic) acid. Acid interacts with milk proteins to make them clump. (Some harmful bacterial spores also survive pasteurization, which is why milk should be kept in the fridge, and should not be consumed if the milk is spoiled.) rapidly spoiled from bacterial growth, but given time, mould would likely have grown in the milk too. Milk provides a host of nutrients for growth of bacteria and mould.

Breads: The breads will be variable in how much mould grows on them, depending on the conditions.
Shelf life: Bread with a longer shelf life will generally have less mould growing on it. Read out the ingredients to challenge students to figure out why it may stay fresh longer. Preservatives such as calcium propionate and sorbic acid, are added to long shelf-life breads. They inhibit mould and bacterial growth.
Moisture level: Bread out of a bag turns dry very quickly and does not allow any mould growth. Bread enclosed in a bag grows mould as the bread contains some moisture. Bread that is misted with water before putting in a bag will grow a lot of mould. Conclude that mould grows better in a moist environment.
Light level: Moulds generally grow faster in the dark vs in bright light, though this is not universal. (Our breads did not show a strong difference between bread in the light and wrapped in dark cloth, maybe because all the samples were stored on a high shelf which was not well lit).
Temperature: Mould would be expected to grow faster in warmer conditions. This is why we put food in the fridge to slow down deomposition and the spoiling of foods.

Use microscopes to look closely at mould:

Transfer a piece of the mouldy bread to a petri dish to look under the microscope, or place the apple juice dish under the microscope to look at its mould.
Mould reproduces like every living thing. Long wispy hyphae spread out from where a mould spore landed. The hyphae grow over and through the bread/drink. Some hyphae grow upwards, and form spore heads at the top. As the spores at the centre of the mould colony ripen they darken, and the dark colour spreads outwards as more spore heads are formed. Different moulds have characteristic colours because of their spore colours. Rhizopus (black bread mould) has black spores, Neurospora (red bread mould) has red-brown spores, Penicillium has blue green spores in the centre of the colony with a white ring surrounding the colony.
Students should be able to see the long wispy hyphae of the mould around the edge of a colony using 10X or 20X power (see photo of mould on apple juice). With higher power the vertical hyphae with tufty spore heads may be visible, though individual spores are too small to see (see photo on bread; compare to web image: http://2.bp.blogspot.com/-m6wEVx0nI4g/ULobDEplvAI/AAAAAAAAIKc/Tju6woNRn…).
Watch a video of mould growth in slow motion, to show the hyphae growth, followed by spore formation and darkening. https://www.youtube.com/watch?v=JsQHWj2RfXg is a beautiful video.

Tape the safety pins to the popsicle stick supports, with the small hole facing upwards. Make sure they are at the same height.
Push the candles in the ends of the straw. Find the balance point of the straw. Poke the straightened paper clip through the straw, then balance between the small holes in the safety pins. Turn the end of the straight wire so that it does not fall out of the safety pins.
When both candles are lit, they will see saw as wax drips from one then the other and their weights change. The see saw will spin all the way around too.