ingridscience

Make sausages out of the modelling clay, and secure them to the tray to make the walls of a track across the tray.
Add water to the tray to fill the track, but not go over the tops of the walls.

Cut out a flat boat from the cardboard. Cut a notch in the back of it.
Place the boat at the beginning of the track.

Dip the toothpick in detergent, then touch the water in the notch of the boat.
It will move along the track.
The boat will move maybe once more before the tray needs to be emptied and refilled with detergent-free water.

Why does the boat move?
The surface tension is lowered in the area where the surfactant is added, and the higher surface tension in front of the boat pulls the boat forward. As the detergent spreads through the water, it decreases the surface tension throughout the water, and the boat stops moving eventually because there is no longer a difference in the surface tension.

By carefully lowering a paperclip onto the surface of the water, it will float.
If you are having trouble, use another bent paper clip to lower it onto the water surface. Remove the bent paperclip from underneath once the other one is floating.

How many paperclips can you float at once?
They will tend to attract each other.

Dip the toothpick in the detergent, then dip it in the water next to a paperclip.
The surface tension will be disrupted and the paperclip will sink.

At the surface of water, the water molecules attract each other relatively strongly so are pulled inwards.
This gives water droplets their round shape, as well as making the surface of water behave as if it has an elastic skin.
Light things are held up by this skin, such as water striders, and paperclips.

Detergent molecules interact with the water molecules and reduce the surface tension of the water.
Hence the surface of the water is no longer able to hold up light objects.

Open the soda.
Add a few raisins (or pour soda into a cylinder or tall jar, then add the raisins).
Watch them rise and fall.

The soda water is water with carbon dioxide gas dissolved in it.
The carbon dioxide in the soda comes out of solution and attaches to the raisins.
This decreases their overall density, so they float to the surface.
At the surface, the bubbles pop, the raisin becomes more dense than the liquid again, and sinks.
The cycle repeats.

The activity can be extended:
1. Ask students to cap their bottle and watch. The raisins will slowly stop dancing. The gas pressure in the air space at the top of the bottle prevents as much carbon dioxide gas from coming out of solution. When the cap is released the raisins will start dancing again as gas is able to come out of solution once more, and sticks to the raisins. This capping and uncapping cycle can be repeated.
2. Ask students to shake their bottle, then slowly release the cap to expel the released gas. With less (or no) gas in solution, the raisins will not dance as fast (or at all).

Fill the bottle with water, to the brim.
Fill the eye dropper half full with water, until it just floats in the top of the bottle.
Top up the bottle with water and cap.

Squeeze the bottle to make the pipette sink.
Release to make it float again.

When the bottle is squeezed, air is compressed in the dropper as water enters it. This makes it more dense, so it no longer floats in the water.
When the bottle is released, the water leaves the pipette again, the pipette contains more air again. The air is therefore less dense again, so the pipette floats.

Human divers use weights to increase their density when diving.
Lifejackets decrease density, to enable a person to float better.
Submarines use tanks of compressed air to control their buoyancy. When ballast tanks are filled with water, the submarine sinks. When the ballast tanks are filled with air from the tanks, the submarine's overall density is decreased so it rises.

This activity is messy, and best done in a tray. Probably not suitable for a whole class, but for breakout groups with an attending adult.

Add a puddle of oil to one glass plate, spread out a little, then sprinkle iron filings on it.
Slowly lower the second glass plate, to avoid air bubbles. Add more oil from the edges with a pipette if necessary.
Move the top glass plate in a circular motion over the lower glass plate, to spread out the iron filings.
Use a magnet over the top glass plate to draw patterns in the iron filings.
Once a design is completed, slide a coloured piece of paper below the lower glass plate, being careful not to get oil on it, then photograph.

Remove the insulation from the last couple of cm of the magnet wire, at both ends, with the sandpaper.
Wrap the magnet wire around and around the pen, to make a coil. Leave 4cm at each end free. Remove from the pen and twist the ends together a few times to secure the coil. The uncoated ends should not be touching.
Tape the coil to the bottom of the cup, with the coil lying flat.
With the headphones removed from the headphone jack, strip the insulation off to reveal the bare wires underneath. Twist any strands of wire together to hold them together. Twist each headphone wire around each of the magnet wire ends, then wrap each in foil to make a good connection.

Start the music on the music player, plug in the headphone jack and turn up the volume.
Hold the cup against your ear with one hand, and hold the magnet against the coil with the other.
You should hear the music, maybe quite quietly. A stronger magnet, or multiple magnets, will make it louder.

The electrical signal through the coil from the music player, turns the coil into an electromagnet. The magnetic field changes with the changing electric signal of the music.
When the magnet is placed against the coil, it alternately attracts and repels the changing electromagnet's field, so pushing then pulling the coil away from it. This pushes the bottom of the cup in and out, which in turn, pushes the air near it back and forth. This is a sound wave is magnified by the cup, so that we can hear it.

Cap each end of a stick with 3 or 4 repelling magnets along the stick.
Students free play with their own stick.

Please note that in a class of students it is likely that one of them is at least partially colourblind (1 in 12 males are colourblind). As this is an activity distinguishing colours, these students will not be able to tell some colours apart and perceive some colours differently, although the activity will be no less interesting for them. The common red/green colour blindness means reds and greens (or colours containing reds and greens such as browns) look similar. More information at colourblindawareness.org and colorblindguide.com/post/the-advantage-of-being-colorblind.

Add a candy and only a drop of water to a well of the paint tray.
Use a stick to turn the candy over and release the colour from its coating. Add one more drop of water if necessary, but keep the colour as concentrated as possible.

Cut a strip of filter paper the correct length to hang into the tub from the skewer with a binder clip. It's end should be about 1.5cm above the bottom of the tub.
Then remove the filter paper and add 1cm water to the tub.

Add a drop of candy dye to one end of the filter paper, at least one cm from the end, using the stick dipped in the candy juice.
Allow it to dry a little, then add another drop, allow to dry, then add another drop.

Attach the binder clip to the end of the filter paper strip away from the dye drop.
Slide the binder clip onto a skewer and lay the skewer over the top of the tub, so that the filter paper just touches the water, but the spot of dye is not immersed in the water.

Allow the chromatogram to run for several minutes, until the colours have moved most of the way up the filter paper.

The colours have different abilities to dissolve in water, and attach to the filter paper surface. All the coloured molecules move with the water, then stick on the paper, then move with the water again, but each different colour sticks to the paper or moves with the water to different extents. Hence the colours move at different rates up the paper and are separated out.

Try with different coloured candies to find out what colours make up each dye.
Compare different candies to see if the same colour is made up of the same component colours.