ingridscience

As described on the Exploratorium website (www.exploratorium.edu/science_explorer/hoopster.html):
Cut the card into strips, about 1 X 5inches long.
Tape one piece into a loop, and another two into a larger loop (by taping them end to end first).
Tape the loops onto each end of a straw, lined up with each other.
Throw the hoopster like a spear. It will rotate and fly quite well.

Play around with variations on the basic hoopster, and compare how they fly (make sure to have several trials with each):
change the number of loops
change the orientation of the loops
change the length of the hoopster by adding straws (push one end into another)
add weight with paper clips or modelling clay
etc. etc

Discussions of the forces involved:
The forward motion is called thrust and is generated by our arm pushing it forward.
The air moving around the loops gives it lift so that it can fly for a while.
Air resistance eventually slows it down and gravity brings it to the ground.

Free experimentation in small tubes:
Instruct students to half fill a small tube with room temperature water. Then drop in one or more of the water types (salty/cold/warm). Watch whether the drips sink or float. Use coloured pencils to show observations. Then try adding different combinations of water to see where they settle.

In general, salty water will settle lowest, then cold water, then warm water will stay on the top (note that after adding salty water, the salt mixes in and will make the whole tube salty, so that cold water will stay near the surface, sometimes even above a red layer (that is warm but now has some salt mixed in). Students will get their own unique results depending on what order and how much of each water type they add. They should be encouraged to look closely and observe water flowing in the tube when they add each type.

Modelling world-wide ocean currents
The heating of the surface of the ocean, and freshwater flow into the ocean changes the temperature and salinity of the ocean. Warmer water is less dense than cooler water, and saltier water is more dense than less salty water. Denser water sinks below less dense water, so the differences in temperature and salinity causes water to move, driving ocean currents.
The thermohaline circulation of ocean water (called the ocean conveyer belt) flows around the world. Warm water from the Tropics is driven North by wind. In the North Atlantic it cools. Evaporation and ice formation in the North also makes the water more salty, making it more dense. The cooler, saltier water, sinks, displacing the bottom water, which flows south beyond the equator to Antarctica. These cold bottom waters flow around the globe and eventually mix with warmer water and move to the surface in the Pacific and Indian Oceans. The cycle is completed when warm surface waters head north again.
http://www.nasa.gov/images/content/436189main_atlantic20100325a-full.jpg
https://en.wikipedia.org/wiki/Thermohaline_circulation
Surface Ocean Currents: Gulf Stream (North Atlantic Ocean), Brazilian Current (South Atlantic Ocean), Agulhas Current (Indian Ocean), Kuroshio Current (North Pacific Ocean), East Australian Current (South Pacific Ocean).

Ocean mixing feeds the animals of the ocean.
Cold Antarctic surface water sinks, forcing the nutrient-rich deep water to rise (40 million cubic meters/second). The nutrients feed algae and other plants, which feed krill, which feed baleen whales, as well as penguins, seals, and seabirds.
Try this video on Antarctic krill - http://oceantoday.noaa.gov/animalsoftheice_krill/ (The krill themselves cause vertical ocean currents as they swim on mass to feed on algae at the surface. Nutrients are drawn upwards in their current.)

Ocean currents are used by animals for migration.
Loggerhead turtles migrate from Florida to the open ocean (where the young are safer), then return as adults. Atlantic Leatherbacks travel from Caribbean to Nova Scotia to feed on jellyfish. Pacific Leatherbacks have the longest migration on Earth: they are born in Japan, migrate to Mexico to feed on crabs, then head back to breed, nest. The Green Sea Turtle rides the East Australian Current, though does not go out into the open ocean (Crush in Finding Nemo).

Modelling air flow in our atmosphere
Air is warmed by the sun, predominantly at the tropics. This warm air rises, and cooler air sinks (just as the warm water rises and the cool water sinks). This movement of air in our atmosphere creates winds.
In addition, ocean currents, caused by differences in temperature and salinity of the water, move heat around the globe.

To demonstrate larger scale cold, warm and salty water flow and layering in a clear-sided box
Fill the box with room temperature water.
Elevate one end of the box to make a sloped bottom.
Drip each of the water types (salty/cold/warm) in turn and watch them sink (salty/cold) or float (warm) in the water, and flow along the bottom or surface.

Mix 3:1 water:soap in a bottle or tray, gently to keep bubbles to a minimum. Add a couple of drops of food colouring.
Move the water around: tip the bottle back and forth or drag a finger through/blow on water in the tray.
The pearlescent particles show the movement of the water.
Watch the swirls (turbluence) in the water, and find the sometimes unexpected patterns that result from water flow.

For discussion on ocean currents:
In the ocean, tides and winds push the water around. Obstacles such as land or underwater mountains create turbulence as the water hits them. All this movement of the water, much of it turbulent and moving in complex patterns, both on a large scale (e.g. along a coastline) and small scale (e.g. around a reef) churns and mixes the oceans' water.
See http://naturedocumentaries.org/839/perpetual-ocean-nasa/ “Perpetual Ocean from NASA” for excellent video of turbulence patterns in the world's oceans.
Water movement brings food to animals that can't move, and moves nutrients and heat around.
Some animals have a profound effect on ocean water mixing e.g. krill move en masse to the ocean surface to feed on algae, creating a moving current of water that brings nutrients from the bottom of the ocean to the surface. Phytoplankton (single-celled plants) at the ocean surface can then feed on these nutrients. When they die they sink to the bottom, cycling nutrients back to the deep ocean. http://www.antarctica.gov.au/magazine/2006-2010/issue-15-2008/science/k….
Some animals use these ocean currents to migrate: Loggerhead turtles migrate from Florida to the open ocean (where the young are safer), then return as adults. Atlantic Leatherbacks travel from Indonesia to Nova Scotia to feed on jellyfish. Pacific Leatherbacks have the longest migration on Earth: they are born in Japan, migrate to Mexico to feed on crabs, then head back to breed, nest. The Green Sea Turtle rides the East Australian Current, though does not go out into the open ocean (Crush in Finding Nemo).

For discussion of the movement of air in our atmosphere:
The turbulence patterns in the tray are the same as the turbulence patterns made by air flowing in our atmosphere (as both water and air are fluids, so behave similarly). When air flows past islands, mountain ranges or other obstacles, turbulence patterns are created. Visual of atmospheric turbulence patterns shown by clouds: http://visibleearth.nasa.gov/view.php?id=72646
Live interactive map of Earth’s winds across the surface: https://earth.nullschool.net/#current/wind/surface/level/orthographic=-…

Focus the sun's energy on one point with a magnifier.
Test different materials to see if they can ignite. Do not stare at the focused spot of light for long - it will hurt your eyes.
(Dried grass ignites but printer paper does not.)
The magnifier focuses the sun's energy to a point, which is hot enough to ignite things that are really thin and dry.

Show the materials to the students.

Tell them that they will build their own devices that can make itself fly, or shoot a small object made from the materials, in a safe manner.
Introduce the idea of elastic potential force - the energy stored in a stretched elastic band or balloon can be used to fire. When the elastic returns to its original shape, it loses energy, and the energy is transformed to motion energy of the projectile.

Support original ideas, constant modification, while guiding to make the design better.
Encourage device development if necessary by breaking down the components of the device: what will produce the power (e.g. elastic band, balloon), what will be the structural strength (e.g. chopstick, possible stick, straw), and projectile (e.g. balled up paper, toothpick).

There are an infinite number of possibilities as to what they can build.

To make a sheet of sugar crystals:
Combine the sugar and water in the heat-proof container. Heat on a stove top to dissolve the sugar, stirring to help the sugar grains dissolve. Be careful not to heat it to much so that it boils over. The sugar solution is very hot, so best if an adult handles it while heating.
Pour into a shallow baking dish, or leave in the container it was heated in. A shallow layer will yield more crystals.
Place in an undisturbed spot. Crystals are seen in two days, a week is best to allow the crystals to grow larger.

The crystals form as the sugar molecules dissolved in the water come out of solution, to form a solid.

Crystals grow down from the surface or up from the bottom of the tray. Chip out a group of crystals and rinse very briefly in cold water to remove the sugary syrup. Allow to dry. Look for the shape of the sugar (sucrose) crystals. They are monoclinic prisms.

To make sugar crystals to eat:
Students will love to eat the crystals that they make. They are pure sugar, so very sweet - only a small amount for a child is needed.
After pouring the hot sugar solution into a baking dish, lay over the mesh. Students write their name on a popsicle stick, then are assisted in lowering the popsicle sticks through the mesh into the sugar solution. Use a clothes peg to support the stick on the mesh.
Crystals will grow on the popsicle stick where it is immersed. The sticks will need to be chipped out of the layer of crystals that form on the top of the sugar solution. Once the syrup is licked/washed in cold water off the crystals, their shapes can be seen quite well.

Tell students that as a crystal grows, the atoms add on in a regular way. Depending on the pattern that the organize in, different shaped crystals are made.
This activity uses building toys to show how a regular arrangement of smaller units can make some common crystal shapes.
When you build, make sure that you add the units in the same repeating pattern (show example).
See which crystal shapes you come up with.

Students model two masses orbiting together. They represent the coupled orbits of two stars (a "binary star system"), or a star orbiting a black hole, or a planet orbiting a star. The movement - the orbit path and speed - of each mass depends on the relative sizes of each object.

Tell students that they will investigate coupled orbits, to discover how orbits and speeds vary with the masses, and then find out how astronomers study couple orbits to discover objects in the universe.

Give students the equipment, ask them to add masses to each end of the skewer. They should try both equal-sized masses, and unevenly-sized masses during their experimentation. They should then make sure the masses are balanced i.e. the skewer is horizontal.
For the masses supported by a post they should find the appropriate hole to put the pin through. For the masses supported by string they can slide the string along the skewer until the balance point is found.
Once the masses are balanced, they can be spun slowly around each other.
Students should note the path that each mass takes and the size of its orbit. For the mass on a post, a flashlight can be shone from a fixed point above the spinning masses, and the path of their shadows traced on the paper.
Students may also look at how fast each of the masses move, but the size of the orbit is the most important.

They should find that the masses both orbit around the balance point (a small mass does not orbit around a stationary large mass, but they both move around another point).
They should find that with unequal masses, the smaller mass has a larger orbit (and moves much faster) than the larger mass.

Astronomers study couple orbits to discover new objects in the universe. If they find a star in orbit with an invisible companion, they can measure the size and speed of the star's orbit to figure out the size of the invisible companion, and therefore what it might be.
If a star is discovered moving in a large orbit around "nothing", the invisible companion may be a (relatively massive) black hole. The black hole has a huge mass which moves very little, while the orbiting star moves in a large, fast orbit around it. The more massive the black hole, the larger and faster the orbit of the star. In the students' model, their large mass is the black hole and their small mass is the star.
If a star is found to be moving in a small orbit (which will be seen as a "wobble" back and forth), the invisible companion may be a (relatively small) exoplanet with a large orbit around the star, that is too small to see itself. In the students' model, their large mass is the star and their small mass is the exoplanet.
(The wobble of a far away star is measured by reading its Doppler shift as it moves away from and towards us.)

Note that with coupled orbits, both masses orbit around a separate balance point, or centre of mass, called a "barycentre". If one mass is a lot larger than the other the barycentre may be within the large object, but it will not be at its centre. The large mass will still make a (small) orbit itself. For simulations of coupled orbits see the gallery near the bottom of https://en.wikipedia.org/wiki/Barycenter
More information on barycentres and discovering exoplanets: https://spaceplace.nasa.gov/barycenter/en/

Coupled orbits can have more than two objects - our solar system is the coupled orbits of the sun, the planets and other bodies that orbit the sun.
Technically, solar system objects, including Earth, are not orbiting the sun, but the sun and all the masses in the solar system orbit the barycentre of the solar system (which is sometimes outside the surface of the sun and sometimes near the centre of the sun). Try this link for the orbit path of the sun around the solar system barycentre:
https://www.researchgate.net/figure/The-orbit-of-the-centre-of-the-Sun-…

Astronomers are searching for "Planet 9" to explain the orbits of the trans-Neptunian objects (objects orbiting the sun beyond Neptune). The apparent location of the barycentre of the solar system cannot be explained by the known objects orbiting the sun, so astronomers are searching for another mass in orbit.
Try Wikipedia entry on Planet 9 for image: https://en.wikipedia.org/wiki/Planet_Nine#/media/File:TNO-Planet9-Diagr…
See NASA webpage on Planet 9 for more information: https://solarsystem.nasa.gov/planets/planetx/indepth

One line summary: astronomers use the phenomenon of coupled orbits to discover black holes, exoplanets and new planets in our solar system.