ingridscience

Distribute materials to make rainbows, either with one or several methods. These methods separate light into its colours.
White light is a mixture of many colours. Other coloured lights are made up of a mixture of a subset of these colours. See the first photo to see how light colours mix to make new light colours.

CDs/DVDs:
Tip the disc towards the room lights, the sun, or shine a flashlight on them. When light hits the groves in the CD, they spread the light out into its component colours, which line up into a rainbow. See the second photo.

Cut glass or prisms:
A piece of cut glass or a prism in a box can be arranged so that a flashlight shining onto a cut edge of the glass separates the colours of the white light into the colours of the rainbow. See the third photo.
A hanging ornament (sometimes called a "rainbow catcher") of cut glass separates sunlight into its rainbow of colours.

Scratched plastic/diffraction gratings/rainbow glasses:
The scratched lines in the plastic of these materials separate light into its component colours.
White light separates into the spectrum of the rainbow. With objects or light sources that only emit some colours e.g. holiday lights or various coloured objects, they only emit a portion of the whole colour spectrum, so when their light is separated, a reduced range of colours are seen.
(Astronomy connection lesson plan on star spectra.)

Using marker pens, the scratched plastic can be used to find out the primary colours of light (cyan (a light blue), magenta (pinky red) and yellow:
Give students purple or dark blue, green and red markers. Ask them to make a blob of colour on white paper, then look at the blob to see what colours "bleed" out of the sides. They should find that cyan, magenta and yellow appear around many colours. This is because the scratched plastic is splitting up the light coming from the marker pen and splitting it into its component colours - these are the colours that make up light (cyan, magenta and yellow). Just like paint there are also secondary colours, which might be seen where primary colours overlap.

Oil:
A thin layer of oil (e.g. on the road from a car) can also make a rainbow of colours when light from the sun hits it.

With older students, discussion can include how the colours are separated:
The edge of a glass prism, or cut glass, bends each of the wavelengths (colours) of light slightly differently, so that they are separated out. The bending of light is called refraction.
The colours in a CD or scratched plastic, in bubbles or an oil slick are formed by interference. When light is reflected from the grooves of the CD or the top and bottom surfaces of a bubble or oil, the light waves interact with each other. Interference of the waves enhances some wavelengths and cancels others in different places, resulting in a rainbow.

Turn the lights on and of in different combinations while holding a hand up to create shadows.
Experiment to find out what is going on.

With one bulb we get the light coming from it showing on the white wall. If our hand is in the way, we block the light and there is a dark shadow.
With two colours we make a new colour (additive colours of light). Our hand blocks one, leaving the other colour showing in its shadow.
cyan is blue and green
magenta is blue and red
yellow is red and green (red and green receptors in our eye are stimulated by yellow)
With three colours, we make almost white. Our hand blocks one, leaving the mixture of the other two colours in its shadow. We get dark where all three shadows overlap.

Clear a classroom space, or move outside, to run this activity.
It can be run alongside other activities (see lesson plans) so that only a few students are running this activity at one time.

Ask students to choose a pole, and balance it on their fingers. They should do a few trials and count evenly, to see how long they can balance it, on average.
Give each student a lump of play dough.
Ask them to attach the play dough to the pole so that they can balance the pole for longer (several trials also needed). (Younger students can be shown how to push the play dough ball on to the top of the pole; older students can simply be given the play dough and asked to attach it as they wish.)

Once they get a sense of how the play dough makes a difference to how long the pole can be balanced, they can try different pole lengths/different sizes of play dough balls/different positioning of the play dough on the pole.
Give students some time to experiment, exchange ideas and to start formulating their own ideas to test.

Then ask students to think about the forces involved in keeping the pole upright.
Why do they think the play dough at the end of the pole allows them to balance it longer? (The explanation is complex, but encourage students to think about, and test out, their ideas around the forces involved.)

Gather as a group to discuss the students' discoveries and ideas, including discussions of their ideas about the forces involved.
No answers are wrong if they are reporting what they observed.

Explain how it works (though not necessary, especially if there is plenty of inquiry going on already which might be halted):
When the pole has no play dough attached, the top end of it tips over quite fast. Our hand has trouble moving fast enough to adjust to this to right the pole again, so the pole falls over quite rapidly. With the play dough at the top of the pole, the pole tips over more slowly and gives you more time to adjust your hand underneath it, so you can hold the pole upright for longer.
The top of the pole moves more slowly with the play dough mass attached because with the extra mass more energy is needed to move the top of the pole. With no mass added, less energy is required to move the end of the pole and so it moves faster. (Try flapping a pole back and forth with weight at the end - much harder than with no weight).
(Explanation in more advanced terms: the further the mass is from the pivot point, the more energy it requires.)

If the above explanation is discussed with students, they might want to experiment further with moving the mass to different positions along the pole and comparing how easily the pole tips over (or how easy it is to flap the pole back and forth).

For the balloon on the line:
Blow up the balloon and either hold it closed, or clip it with the binder clip to stop air escaping.
Attach the balloon to the straw with tape.
Release the balloon go.

For a simple activity, but one that is hard to control variables, the balloon can just be released into the air.

The force of the air rushing out pushes back on the balloon, making it move. (Newton’s 3rd Law: for every action there is an equal and opposite reaction).

Variables to explore:
1. Ask students to blow the balloon up to different amounts, and compare how far it goes each time.
2. Try adding mass, for example by adding pennies to a pot that is attached to the straw. If students are old enough to blow the balloon up to a consistent diameter/length, the results can be graphed for a visualization of this inverse relationship. For younger students the data is quite messy, I think because the balloons are not consistently blown up, and from other variables, so discussion can be around which number of pennies the balloon went the furthest (generally low numbers of pennies) and the balloon went the least far (generally high numbers of pennies).

The same principal is used to make rockets go into space. Rocket fuel is burned to produce a gas (see molecular modelling of real rockets). The gas produced builds up to enormous pressures and is released out of a small hole called a nozzle (like in your balloon). The gas rushing out of the nozzle from the back of the rocket, pushes the rocket upwards.
For discussion around the added mass, fuel is a significant mass in the weight of a rocket, so makes a large difference in how fast the rocket can be moved. The amount of fuel needed is calculated very precisely to eliminate any extra mass.