ingridscience

This activity taken from Society of Physics Students outreach manual: https://www.spsnational.org/sites/default/files/files/programs/2012/soc…

Tell students they will be using the gravity well to model the shapes and speeds of orbiting objects. They release their marble so that it orbits the centre well of the fabric. The centre well models the gravity of the sun/a star/a black hole (depending on the emphasis of the lesson). Their marble may model a planet, dwarf planet, asteroid, comet orbiting a star. Or their marble can model a star orbiting a black hole.
(See below for comments on how this model is different from real astronomical objects in orbit.)

As students experiment, prompt them to notice the shapes of the orbits they make, and maybe also the speed of the marble at different distances from the well.

Discussion on orbit shapes
Ask students what shaped orbits they made, and compare their descriptions to orbit shapes of astronomical objects. Our familiar planets have a circular orbit, whereas comets and several trans-Neptunian dwarf planets have elliptical orbits.
Show images of various orbits (of planets, moons, dwarf planets, asteroids, Kuiper belt objects and comets), during experimentation or after.
Try this image for comet orbits: http://www.wired.com/images_blogs/wiredscience/2013/08/Orbits_of_period…
Try this page for images for orbits of dwarf planets in the solar system, to give a sense of how many objects orbit the sun: http://www.duncansteel.com/archives/2140 or do an image search of "orbit Eris Haumea Makemake").
Discussion on why objects orbit: they are continually "falling" towards the sun, or central gravity well, but as they are in forward motion, they never reach it, but instead curve around it.
Note on why our planets' have a circular orbit: maybe because they were formed from a spinning disc of debris, so all end up in the same plane. Also, if they were not circular, we would not be here to observe them! (Our distance from the sun would change a lot, making a challenge for life to survive.)

Kindergarteners and young primaries can draw the shapes they made with their marble: circle, elipse, long narrow elipse, star shape as the ellipses cycle round. Orbits in the galaxy are all these shapes.

Several marbles orbiting at once can represent the asteroid belt, with collisions that knock some of them out of orbit.

Using the gravity well to model stars orbiting a black hole
Stars orbit black holes, so astronomers look for stars that appear to be orbiting around "nothing", as evidence for the presence of a black hole. By mapping the locations of all objects in orbit, the location and size of the black hole can be calculated.
Show students an image of star orbits around a black hole. Try this image, or search images for "SgrA* orbits": https://inspirehep.net/record/800608/files/f16.png
To modify the gravity well model to be more like the shape of the gravity well of a black hole, add a ring underneath to model the event horizon (the point past which nothing can escape from a black hole's gravity). See the last two photos.

Discussion about orbit speeds
Ask students to notice what happens to the speed of an orbit as the object approaches the gravity well of the sun, as astronomical objects behave the same. They speed up near the object they are orbiting, gaining kinetic energy. As they move outwards they lose speed, but gain another kind of energy - gravitational potential energy. (Similar to a ball been thrown in the air or a roller coaster ride.) Planets with large orbits spend most of their time far from the sun, where they are moving more slowly.
Our solar system is orbiting the centre of our Milky Way galaxy, with average velocity of 720,000km.hr!
A black hole has an event horizon, past which the object cannot escape its gravity, however much energy it has.

Using the gravity well to model how the moon causes tides

Information on classes of objects that orbit the sun
Planets - now 8 planets, as Pluto is now classified as a dwarf planet. To be a planet, an object needs to 1. be massive enough to pull itself into a sphere under its own gravity 2. is not massive enough to cause thermonuclear fusion (like a star) and 3. has cleared its neighbouring region of smaller objects i.e. they are attracted by its gravity.
Dwarf planets - large enough to be spherical, but too small to clear their neighbourhood of smaller objects. There are many many dwarf planets orbiting the sun, and more are continuously being discovered. Examples: Ceres in the asteroid belt, Trans Neptunian objects (TNOs) such as Pluto, Eris, Makemake, Haumea.
Asteroids - small irregularly shaped objects made of rock, metal or a mixture of both, found in the asteroid belt. Image of main asteroid belt at: http://www.rawscience.tv/wp-content/uploads/2014/09/asteroid-belt.jpg
Comets - snowballs of frozen gases, rock and dust the size of a small town. A comet warms up near the sun and develops a coma (atmosphere), a glowing head, hundreds of thousands of km across. It has two tails (which always point away from sun), one gas and one dust (which curves with sun’s gravity). Image of comet structure through its orbit: http://www.skyandtelescope.com/wp-content/uploads/Koehn_IZ_orbit_300dpi… Comets may have brought water and organic compounds (the building blocks of life) to Earth and other bodies in our solar system. There are billions of them. Image of some comet orbits at: http://www.wired.com/images_blogs/wiredscience/2013/08/Orbits_of_period… (Orbit times: Halley orbit is 76 years, Borrelly orbit is 7 years, Ikeya–Zhang orbit is 366 years and is the longest known orbital period.)

Differences between this gravity well and real orbiting objects
Ask older students for ideas in how their model is different from real orbiting objects at the end of this activity.
In this model, every marble inevitably loses energy to friction as it rubs against the cloth and falls into the gravity well. In the vacuum of space there is no friction, and orbit shapes are maintained, as long as there are no collisions.
Physicists use this kinds of model of gravity, though they would use mathematics to describe the shape of a gravity well, rather than a physical object. The more massive the body, the deeper and more extensive the gravity well associated with it. Black hole has a very deep well.

Activity adapted from NASA 'Impact craters':https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf

This is most easily run as a group activity, with one or two trays on a carpet, with students in circle(s) around the tray(s).
It can also be run with a tray for each table group.

Introduce the activity:
In the solar system, chunks of rock sometimes collide with planets or moons.
These stray small chunks of rock and metal most often come from the asteroid belt (between Mars and Jupiter), when a collision between asteroid belt bodies sends an asteroid out of the belt into the rest of the solar system.
Asteroids come in various shapes (as they are not large enough for gravity to pull them into a sphere): https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg
Impact craters, from when a "meteoroid" hits the surface, are the dominant geographic features on many solid Solar System objects. (Early in the history of our solar system, asteroid impacts were much more common. Now, many of these stray chunks of rock have been caught by the gravity of big planets.)

Shake a tray of flour back and forth so that the surface of the flour is relatively flat. Do not press the surface down - allow it to settle with its own weight. Place the tray on the floor.
Sprinkle cinnamon over the flour to make an even coat of brown over the flour.
Optionally ask students to make asteroid-shaped pieces with their modelling clay. (Show them shapes from here: https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg)
Allow students to drop the marble/clay ball from a height above the tray, taking turns.

Name the parts of the crater that are formed:
The floor of the crater (the bottom of the hole), the rim (the raised edges ringing the hole), ejecta (material projected out of the crater - it will look white in contrast to the brown cinnamon), rays (long lines extending away from the crater; a pattern made by the ejecta).
(See p.3 of Activity adapted from: https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf)

Students can observe that different clay asteroid shapes all make circular impact craters (as long as they are going fast enough).
Students, or a teacher demonstration, can model an 'oblique impact' crater - an asteroid hitting a planet surface at an angle (either with a throw from the side, or by tipping the tray). The crater made has ejecta concentrated on one side (see last photo). Easier to see properly on a new layer of cinnamon.
Students can try dropping their 'asteroids' from different heights (therefore different impact speed), to observe the difference in the crater sizes made.
Optional: ask students to measure the heights they are dropping from and to measure the diameter of the crater from rim to rim in each case. (Note that this data is messy and there is not a huge amount of difference between high and low drop heights, but it demonstrates graphing data, and how to draw lines of best fit. See worksheet attached.)

Once the flour and cinnamon is covered in impacts and it is hard to see the patterns, stir up the flour and cinnamon to make an even colour, then reapply the cinnamon..

Discussion points and more information:
1. Students should find that the crater diameter is always larger than the asteroid. When the surface of a real planet or moon is hit by a chunk of rock (more precisely called a meteoroid, or the "impactor"), the shock fractures the surface rock and makes a large cavity which is larger than the impactor. The impact sprays material ("ejecta") in all directions. (Any remaining rock pieces are called meteorites.) Asteroids hit the moon at an average of 20 kilometers per second, and make a crater 10 t0 20 times larger than the impacting object.
2. Point out to students that the marble/clay stays in the hole - for a real crater the impact rock has gone. It has shattered and been distributed with the ejecta. Or if the impact generates enough heat, the impactor melts or vapourizes.
3. Either through eye-balling the difference in patterns, or by graphing data collected, the size of the crater and the average ray length increases with impact speed. (See graph of data - it is messy, but a line of best fit shows the trend.)
4. Show students an image of real craters and ask if theirs looked similar
e.g. on Mercury: https://assets.science.nasa.gov/content/dam/science/psd/photojournal/pi… and https://science.nasa.gov/resource/the-impressive-rays-of-hokusai/
e.g. on the Moon: https://myearthscience.com/wp-content/uploads/2017/11/crater-rays-moon….
Next time students see a full moon, they might be able to find the crater rays on it: https://upload.wikimedia.org/wikipedia/commons/2/2d/Full_Moon_%28159847…
5. Show students a real oblique impact crater: http://lroc.sese.asu.edu/posts/595

What do craters tell astronomers?
Scientists figure out the speed of an impact by the size of the crater formed. They also look at other features that are made with the very high speeds of meteorites hitting moons and planets - sometimes craters have central uplifts and terraced walls that give more information about the impact, and the rock on and under the surface of the planet.
Craters with different features are sometimes formed. e.g. Rampart Craters on Mars (https://en.wikipedia.org/wiki/Rampart_crater). There are no rays. Water or ice present under the impact site melted with the impact, then flowed away instead of being thrown away from the crater. This pattern of ejected material can be used as a way to identify areas with possible water or ice in the surface layers of a planet.
The number of craters on a surface can tell scientists about a planets geology and atmosphere:
Many craters indicate that there is no atmosphere to burn up the rocks as they come down. (e.g Mercury). It also may indicate that there are no plate tectonic movements or erosion turning over the planet’s surface. Earth and Venus have an atmosphere, which burns up rocks as they hit it (called "meteors" or "shooting stars"). Earth also has moving tectonic plates and erosion that recycle the rocks, so removing craters. (The craters on the Moon are good for studying crater formation, as the Moon has no atmosphere, plate tectonics, or moving water (which all erode a surface and erase all but the most recent impacts).
http://mars.nasa.gov/education/modules/GS/GS38-49.pdf

Introduction:
Images of planets’ surfaces sent back to earth often have abstract patterns that need to be interpreted.
Scientist use their knowledge of the formation of features on Earth and other background knowledge they have about a planetary body to identify geologic features of planets and hypothesize about how those features may form on these other worlds.
Two kinds of features are "aeolian": formed by wind, and "fluvial": formed by a liquid.
Scientists use their knowledge of what kinds of patterns liquid water and wind make to find out if the planet did have/has running water (or other liquid), and has wind (therefore an atmosphere).

Students make patterns with wind and water:
Aeolian (wind) patterns are made by spreading sand evenly in a tray, adding two rocks to one end of the tray, and blowing the sand along the bottom of the tray from the other end. A plexi sheet covering most of the tray prevents sand from blowing out of the tray. The sand is blown from around the rocks, but remains in a streak behind the rocks (see first two images).
Fluvial (liquid) patterns are made by swirling a tray of sand and water to mix them evenly, then tipping the tray so that the water runs through the sand, creating channels. (See third image).

Students compare the patterns they make to those seen on other planets, and deduce what formed each of the pictured planetary features. (See fourth image, and links below.)

Discussion:

Mars features are both fluvial and aeolian:
A drainage network of a liquid is clearly seen. There is no liquid on Mars now, only ice water. This fluvial feature is from extensive water flow in the past when Mars was warmer. Why was Mars warmer? Maybe it had an atmosphere to create a greenhouse effect. Or maybe asteroid and comet impacts which filled the atmosphere with vaporized rock and ice, resuled in several years of rainfall and flooding that formed the fluvial erosion features.
The wind streaks seen on Mars are from erosion of the surface rock. Erosion needs an atmosphere - a gas that can move past the surface and carry dust particles along. This is happening on Mars now - we have seen tornadoes on Mars.
We also see dunes on Mars, evidence of aeolian activity.

Venus feature:
Wind streaks are seen. Winds are from carbon dioxide atmosphere blowing fine-grained particles around.

Titan (moon of Saturn) feature:
Drainage networks from a liquid are seen. They are formed by liquid methane! Venus has a methane cycle: it rains methane, which flows into methane rivers and lakes, from which it evaporates and rains again (just as we have a water cycle).

Images and information from the NASA ARES site resource. Specific web links:
Visual summary of how different planetary features are formed at https://ares.jsc.nasa.gov/interaction/eeab/pdfs/bmm/bmm_quickreferences…
Images of various planet features at https://ares.jsc.nasa.gov/interaction/eeab/pdfs/bmm/bmm_planetaryfeatur…

Before the class, map a route that extends from the classroom to 300m away, using streets that keep the route on a straight line as possible.
Google maps has a "measure distance" feature which works well for mapping the route and the location of each planet.

Inform students that we will make a 1:10,000,000,000 scale model of the solar system. Discuss what a scale model is if necessary.
Together with the students, write up the planets in order.
Stick the sun image to the board, and ask students that if the sun in our model has a 10cm diameter, what's their guess on how large would the other planets be? Add the scaled dimension of each planet to the list, while discussing relative sizes of the planets.
Assign each table group to one planet, that they will make to scale. (The inner planet or two can be done by the teacher to demonstrate the method if there are more planets than student groups.)
Either give them a sheet showing the planets' colours, or list the planets' colours from students' knowledge.
Then distribute the modelling clay colours that the students need to make their scaled planet. If they use a couple of colours, the larger planets can have a swirly pattern that mimics the planet's appearance.

Distances calculated using https://www.exploratorium.edu/ronh/solar_system/
If you want to add in Earth's Moon to scale, its diameter is 0.2mm and it orbits 2.5cm from Earth. Other planets have moons too.
(See this activity for modelling just the Sun, Earth and Moon to scale.)

Once their planets are made, discuss and fill in the scaled distance from the sun to each planet.
Ask students to place their planet in a tub (so that they don't get lost) with their distance written on it.
Using the metre stick or tape measure, have the students calibrate their pace to a metre.

Group by group, the students pace from the sun and out to each planet in turn, pacing out the metres. The rest of the class follows the planet that is being placed.
After only one or a couple of inner planets, the scale model will leave the classroom and head outdoors. The outer planets will be off the school grounds into a park or street beyond.

Pause at Earth to remind student that the planets are in orbit around the Sun, and note that we are orbiting the sun at 30km per second!
Other features to optionally include on the walk: the Asteroid belt is between Mars and Jupiter and the Kuiper belt (which includes Pluto) is beyond Neptune.

Once at the final planet, pause to reflect on how far the group has walked, how tiny the planets are on the way, and that between them is empty space.
Walking back along the route, and finding the tiny planets along the way reinforces how large the solar system is and how small the planets are in it.

Information on classes of objects that orbit the sun
Planets - now 8 planets, as Pluto is now classified as a dwarf planet. To be a planet, an object needs to 1. be massive enough to pull itself into a sphere under its own gravity 2. is not massive enough to cause thermonuclear fusion (like a star) and 3. has cleared its neighbouring region of smaller objects i.e. they are attracted by its gravity.
Dwarf planets - large enough to be spherical, but too small to clear their neighbourhood of smaller objects. There are many many dwarf planets orbiting the sun, and more are continuously being discovered. Examples: Ceres in the asteroid belt, Trans Neptunian objects (TNOs) such as Pluto, Eris, Makemake, Haumea. Try this page for images of their orbits: http://cnx.org/resources/66fc832ba8fa89f299d718228e06c7cb0ad85924/OSC_A… and this page to show more dwarf planet orbits: http://www.duncansteel.com/archives/2140
Asteroids - small irregularly shaped objects made of rock, metal or a mixture of both, found in the asteroid belt. Image of main asteroid belt at: http://www.rawscience.tv/wp-content/uploads/2014/09/asteroid-belt.jpg
Comets - snowballs of frozen gases, rock and dust the size of a small town. A comet warms up near the sun and develops a coma (atmosphere), a glowing head, hundreds of thousands of km across. It has two tails (which always point away from sun), one gas and one dust (which curves with sun’s gravity). Image of comet structure through its orbit: http://www.skyandtelescope.com/wp-content/uploads/Koehn_IZ_orbit_300dpi… Comets may have brought water and organic compounds (the building blocks of life) to Earth and other bodies in our solar system. There are billions of them. Image of some comet orbits at: http://www.wired.com/images_blogs/wiredscience/2013/08/Orbits_of_period… (Orbit times: Halley orbit is 76 years, Borrelly orbit is 7 years, Ikeya–Zhang orbit is 366 years and is the longest known orbital period.)

This activity is adapted from a NASA activity no longer available. Similiar activity also at https://www.teachengineering.org/view_activity.php?url=collection/cub_/…

Introduce gravity assist:
We have used rockets to send probes to many parts of the solar system, and beyond.
Show image of current position of probes: https://armchairastronautics.blogspot.com/p/solar-system-missions.html
For sending spacecraft long distances, we need to keep the fuel usage to a minimum, as much of the weight of a rocket is fuel (90%). Rockets use most of their fuel to escape earth’s gravity. Then the gravity of planets or moons are used to alter a spacecraft's path and speed, with only small amounts of fuel needed for course-adjusting thrusts. Using the gravity of other bodies to change the speed and direction of a spacecraft is called 'gravity assist', 'gravitational slingshot', or 'swing-by', and has been used to send probes to the outer reaches of, and beyond, the solar system, as well as closer missions around the Earth's Moon.

Students model gravity assist by using a steel ball (the 'spacecraft' or 'probe'), which is rolled down a ramp ('launched') onto a plexi sheet. Magnets taped to the underside of the plexi pull on the steel ball, modelling the 'gravity' of planets in its path, deflecting the spacecraft as it passes by. The amount of deflection depends on the speed of the spacecraft, how close it passes by the planet and the gravitational strength of the planet.

Show students how to set up the gravity assist activity:
Draw a line down the centre of the plexi, along its length, then set it on the four supports in the tray. Make sure the ramp is taped to point directly along the path. Release the spacecraft down the ramp and make sure it follows the line. If it does not, the desk is not entirely level, so rotate the tray and launch again, repeating this adjustment until the spacecraft follows the line down the centre of the plexi. Then leave the tray in this position. (If a desk is very tipped, the activity will not work so well, so assist students in choosing a level desk.)
Now add a planet: Tape the magnet underneath the plexi, positioned just to the side of the central line and half way along it.
When the ball is released from the top of the ramp, it should reproducibly deflect a small amount around the magnet. If it does not, adjust the height of the ramp or the position of the magnet.

Structured format to activity:
Show students their worksheet (see attachment), for recording how spacecraft speed and gravity of a planet affect the spacecraft's trajectory.
Students change the speed of the spacecraft by releasing the ball from the top of the ramp (faster) or lower down (slower). Increase the gravity of the planet (i.e. a larger planet) by adding magnets underneath the taped magnet.
Show students how to measure the angle of deflection for the different conditions they try: make a mark where the ball rolls off the plexi, and repeat until the marks are consistently on top of each other. Then draw a line from this mark back to the centre line next to the magnet. Use a protractor to measure the angle between the centre line and the angled deflection path.

Discuss class data:
Although there will be much variability in the angles measured (depends on slope of desk, position of magnet etc) , decreasing the speed of the spacecraft by releasing at a lower position on the ramp should generally produce greater angles of deflection. Increasing the gravity of the planet, by adding more magnets, should generally produce greater angles of deflection.
Optionally, a class graph can be made of the increase/decrease in angle when changing from low to high gravity and high to low speed.

Show students trajectories of real spacecraft that have used gravity assist (see below), and challenge students to replicate some of these.

Connection to the Artemis Moon mission
Challenge students to position their magnet, which now represents the gravity of the Moon, so that their spacecraft orbits around the Moon and returns to the launch site on Earth.
With some experimenting with the angle of the plexi sheet, students may even be able to model the figure of 8 trajectory that the Integrity spacecraft made around the Moon and back to Earth. With this trajectory, the spacecraft flies in ahead of the Moon’s orbit before looping around it, and the Moon slows it down and makes it curve back towards Earth. This is called a 'Free return trajectory', as even with engine failure, the spacecraft returns to Earth.
If a spacecraft flies in behind the object it is passing, gravity would sling the spacecraft further out into space. This is useful if this is the desired trajectory, but not if the spacecraft is returning to Earth.

Free experimentation:
After guided measurements and challenges, allow students to place their magnets and launch ramp in any positions and freely experiment.
Some of them will want to employ their own methods e.g. tipping the plexi to combine gravity with magnetic force to direct their ball e.g. purposely placing magnets so that their spacecraft 'crash-lands' on a planet.
Students will be excited to share how they made their trajectories.

End discussion
Conclude with how even a small difference in the speed of the spacecraft or the position/gravity of a planet makes a dramatic change in the trajectory of a spacecraft. Space scientists do all this planning with math! They calculate when a spacecraft must launch (the 'launch window'), and in which direction (to take advantage of the spin of the Earth to speed it up). The calculations include the movements of the planets, so that the spacecraft flies by in a predicted path - whether the probe passes behind or in front of the planet in its orbit determines whether it speeds up or slows down the spacecraft. Gravity assists of close approach only last a few hours. It takes years for a probe to reach its destination planet - the distances are huge. But the math of all the motions and speeds of objects can calculate how to reach these far away objects. Small fuel 'burns' are used to minorly adjust a trajectory and keep a spacecraft on course.

Real gravity assist trajectories (as of Spring 2019):
1. New Horizons flew by Jupiter (and sent back detailed images) to direct it to Pluto. New Horizons is currently in the Kuiper belt.
2. Juno flew by Earth for its gravity assist out to Jupiter. On its gravity assist to orbit Jupiter, it was a slow-down. [Ingrid check]
3. Voyager 1 used gravitational assist from Jupiter and Saturn and in August 2014 entered interstellar space. Voyager 2 swung by Jupiter and Saturn and then also Uranus and Neptune and just entered interstellar space. Animation of the paths of Voyager 1 and 2, showing the trajectory changes from gravity assist: https://www.theplanetstoday.com/voyager_flight_path.html
News article when Voyager 2 entered interstellar space: https://www.cbc.ca/news/technology/voyager2-interstellar-space-1.5274614
4. Cassini (see attached file) was a 20 year mission, to orbit Saturn before descending beneath the rings and into Saturn's atmosphere. It arrived at Saturn with gravity assist from Venus, Earth and Jupiter: https://science.nasa.gov/resource/cassini-trajectory/ The rocket that launched Cassini in 1997 was the most powerful available to NASA, but it still wasn't powerful enough to send the nearly 6,000-kilogram (13,200-pound) spacecraft on a direct course to Saturn. Instead, mission designers planned multiple flybys of Venus, Earth and Jupiter, using each planet's gravity to boost Cassini's sun-relative speed and send the spacecraft out to Saturn.
5. Juice (‘Jupiter Icy Moons Explorer’) was launched in 2023. It will use gravity assist of the Moon, then Earth, Venus, Earth and Earth again, then 223 Rosa (an asteroid) to get to Jupiter’s moon Ganymede in 2031. For animations of trajectory around the Sun, Jupiter and Ganymede (Jupiter Moon): https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Explorer (scroll down)
6. Artemis mission for a simple, but close to home, use of gravity assist. See the lesson plan.

Hydrogen fuel cells
Energy from hydrogen does not make greenhouse gasses, so if storage of liquid hydrogen is possible, it can be used as a clean fuel. However, storage of hydrogen as a compressed gas or cooled to a liquid takes energy.

Rockets
Show a dramatic video of a real rocket taking off e.g. Artemis II for Moon flyby in 2026: https://www.youtube.com/watch?v=PGBoVotHqIE
The core stage rocket in the centre is a hydrogen-fueled rocket, acting after he solid rocket boosters separate at about 2 minutes.

Discuss how real rockets work:
The "rocket fuel" is mixed with an "oxidizer" in the combustion chamber. They chemically react and make new molecules, including a gas. The huge amount of gas produced (called "exhaust") can only escape out of a nozzle built into the back of the rocket. The action of the exhaust shooting out exerts an equal and opposite force on the rocket, which propels the rocket upwards. (Newton's Third Law of Motion: Action and Reaction).
(If the baking soda/vinegar rocket activity or Alka seltzer activity has been done, remind students that it is the same mechanism.)

Model the chemical reaction in fuel cells or LOX/LH2 rockets
Give the students their molecule pieces.
O2 (liquid oxygen or 'LOX' in rockets) + 2 H2 (liquid hydrogen or 'LH2' in rockets).
(In a rocket engine, they are stored at very low temperatures, so are liquid.)
Tell them that in the fuel and oxidant are mixed, and the oxygen and hydrogen chemically react to make a new molecule. Ask them to take apart their oxygen and hydrogens and rebuild two identical molecules.
They should make two water molecules, 2 H2O. They might recognize this molecule when it is called by it's chemical formula.
In a fuel cell the chemical reaction makes heat, water (mostly gaseous) and electricity.
In the rocket the chemical reaction makes heat and gaseous water, which escapes through the nozzle and gives the rocket thrust.

Other facts about rocket fuels:

The fuel is a significant portion of the rocket mass, so as the fuel is burned up, the rocket gets significantly lighter and accelerates upwards.
The boosters (on the side) run out of fuel first, then the main engine.

The propellants of a rocket are often a "fuel" and a source of oxygen "an oxidizer".
The most efficient fuel and oxidizer combination is liquid oxygen (the oxidizer, also called LOX) and liquid hydrogen (the fuel, also called LH2), as we modelled here.
Liquid oxygen ("LOX") is the oxidizer commonly used in rockets.
Other fuels used besides liquid hydrogen are kerosene or methane.
Chemical reaction for kerosene: 2 C12H26(l) + 37 O2(g) → 24 CO2(g) + 26 H2O(g)
Chemical reaction for methane: CH4 + 2O2 → CO2 + 2H2O

A rocket where the fuel or oxidizer (or both) are gases liquefied and stored at very low temperatures (below −150 °C) is called a cryogenic rocket engine. If the propellants had been stored as pressurized gases, the size and mass of fuel tanks themselves would severely decrease rocket efficiency.

Rockets have to carry their own oxygen into space, where there is no air.
This is in contrast to aeroplanes, which use atmospheric oxygen to oxidize their fuel.

"Monopropellants" are just one molecule (e.g. hydrogen peroxide or hydrazine) that can split into gas molecules, with a catalyst to speed up the reaction. Hydrogen peroxide decomposes into oxygen and water gases. Hydrazine decomposes into nitrogen and hydrogen gases. The gases produced are directed through a nozzle to create thrust.

First liquid-fuelled rocket in was launched in 1926. It flew 12metres. First satellite, Sputnik, launched in 1957 by the Soviet Union. 1961 was the first person in space.