ingridscience

Either build the starting molecules, or ask students to make them: one ethanol molecule and three oxygen molecules.

Tell/remind students that ethanol is a fuel that burns in oxygen, and that when the fuel and oxygen chemically react their atoms come apart and recombine into new molecules.
One of those new molecules is water (H2O), and it makes three of them.
Ask students to pull apart their ethanol and oxygen molecules, and rearrange them to make three water molecules.
Then tell them that the remaining atoms and bonds make the other reaction product. There are two identical molecules of this second product.
Give them time to use up all the remaining atoms and bonds to make two identical molecules. With time, they should arrive at CO2, or carbon dioxide.

So when ethanol (or other fuels) burn in oxygen the reaction products are water and carbon dioxide.
Sometimes carbon (as soot) is also made, when not all the carbon combines with oxygen (called incomplete combustion).

Additional information on the flames that are often present during combustion:
The flame is a mixture of hot gases, primarily CO2, water vapour, oxygen and nitrogen (nitrogen comes from other materials that burn).
Energy in the flame excites the electrons in some of the transient reaction intermediates such as the Methylidyne radical (CH) and Diatomic carbon (C2), which results in the emission of visible light (blue and green for these radicals) as these substances release their excess energy.
https://en.wikipedia.org/wiki/Flame

Fill the bottle with water, with a finger over the hole, and hold it over a sink.
Let the water stream out of the hole. Ask a student to shine the laser through the bottle and into the start of the stream.
The laser light will be reflected from the sides of the inside of the stream, so it stays inside the stream of water even as it curves, so lighting up the water stream. There is a point where the stream curves too steeply for the internal reflection to continue.

https://www.youtube.com/watch?v=ifbCsha7Syc

Give students pocket lasers, small mirrors, and tape.

Ask them to reflect the laser around the room.

It is more challenging than expected, as a slight change of angle of the mirror will change the direction of the laser dramatically.

Very fun, but very dusty for other objects in the room: clap cornstarch in the air to visualize the laser beams. Students can design a challenge where they have to crawl under and climb over laser beams without touching them.

Fill the fish tank with water (do not try to move after filling).
Add a few drops of milk and swirl around. The milk will only just be visible. It is easy to add too much.
Darken the room.
Ask students to shine their lasers in the tank, observing what happens when it hits the glass at the sides of the tank, as well as the surface of the water.

The lasers will reflect off the glass, and also the surface of the water, which behave like mirrors. Also interesting is that some of the beam reflects back and some does not, so the path of the laser light is split, so with multiple reflections interesting patterns can be made from just one laser beam.

For more experimentation add mirrors under the water for students to move around.
https://www.youtube.com/watch?v=aN1saYRr6z4

Set up the pulley system as shown, first with just one pulley at table height - the rope passes from the weight and through the pulley only.
Feel the force that it takes to pull the weight up.

Then add a pulley to the water bottle. Pass the rope back and forth between the fixed pulley at the top and the moveable pulley at the bottom, so that four rope lengths are holding up the bottle.
Feel the force needed to lift the water bottle, and compare to the single pulley system previously done.

As more lengths of rope are pulling the weight up, the force needed to pull the rope is less. With four ropes pulling up the weight, the force required should be a fourth.
But in exchange, more rope will have to be pulled through (less force over a greater distance, compared to more force over less distance with just one pulley).

Assemble as pictured.
The rod holding the pen, must be able to freely move up and down, but with out any sideways wiggle. I had to hold with my hands to prevent losening.

Pin the paper to the board.
Add the cans in the corners for weight.
Set the board in motion.
Then drop the pen on the board.
Do not touch anything that will impede the free swinging of the board or the motion of the pen arm.