Tukuk-OSExperiments — Science You Can Touch
Safe, cheap, hands-on — and every one has a real explanation
Twelve safe, low-cost experiments using things already in most kitchens. Each lists materials, ordered steps and the real science behind the result. Items marked medium need an adult for a hot-water or boiling step. The concepts connect directly to the science explainers.
Twelve experiments
Density tower
You need: Honey, dish soap, water, vegetable oil, rubbing alcohol (adult to handle), a tall clear glass, food colouring (optional).
- Pour each liquid slowly down the side of the glass, one at a time, in this order: honey, soap, water, oil, alcohol.
- Watch the layers settle without mixing.
- Drop in a grape and a coin — they stop at different heights.
Why it happens: Liquids stack by density: the heaviest per volume sinks to the bottom. Objects float on the first liquid lighter than them — the same rule that makes ships float and hot-air balloons rise.
Walking water rainbow
You need: Three cups, paper towels, water, three food-colouring colours.
- Line up cups: colour the first and third, leave the middle empty.
- Fold two paper towels into strips; bridge cup 1→2 and cup 3→2.
- Wait 30–60 minutes and watch colour creep uphill into the empty cup.
Why it happens: Capillary action: water climbs tiny fibres against gravity, dragging dye with it. Real trees lift sap to their tallest leaves the same way.
Pepper and soap (surface tension)
You need: A plate of water, black pepper, dish soap, a toothpick.
- Sprinkle pepper over the still water.
- Touch the centre with a dry toothpick — nothing.
- Dip the toothpick in soap and touch again — the pepper shoots to the edge.
Why it happens: Water's surface behaves like a stretched skin (surface tension). Soap weakens it locally, so the stronger water elsewhere pulls the surface — and the pepper — away. Germs behave similarly near soap for the same reason.
Invisible ink with lemon juice
You need: Lemon juice, cotton bud, white paper, lamp or sunny window (adult to supervise any warming).
- Write a message on paper with lemon juice using a cotton bud.
- Let it dry completely — the page looks blank.
- Warm the paper near a lamp or in strong sun; the writing turns brown.
Why it happens: Lemon juice is a weak acid that oxidises and browns before the paper does when heated. Organic invisible inks all work on this early-browning principle.
Static balloon electroscope
You need: A balloon, wool cloth or hair, a thin stream of water from a tap, small paper bits.
- Rub the balloon on wool for 10 seconds.
- Bring it near (not touching) small paper pieces — they jump up.
- Hold it beside a thin tap-water stream and watch the water bend toward it.
Why it happens: Rubbing transfers electrons, charging the balloon. Its electric field polarises the paper and the water, and the opposite charge side is pulled closer — electrostatics, the same physics behind lightning.
Cabbage pH indicator
You need: Red/purple cabbage (adult boils it), clear cups, lemon juice, vinegar, baking soda, soap water, milk of magnesia (optional).
- Adult boils cabbage pieces 10 min; cool and strain the purple water.
- Pour indicator into cups; label each test liquid.
- Add a spoon of each: lemon and vinegar turn pink-red; baking soda turns blue-green; neutral water stays purple.
Why it happens: Cabbage contains anthocyanin pigments that change molecular shape with acidity, reflecting different colours. Laboratories use the same trick with litmus paper and universal indicator.
Bottle "cartesian diver"
You need: A plastic bottle with cap, water, a sauce packet or a pen cap with Blu-Tack (one that just barely floats).
- Fill the bottle completely to the brim.
- Add your barely-floating diver; screw the cap on tight.
- Squeeze the bottle — the diver sinks; release — it rises.
Why it happens: Squeezing raises pressure and compresses the air pocket inside the diver, letting more water in so it becomes denser. Divers and submarines control buoyancy exactly this way, with ballast tanks.
Homemade compass
You need: Sewing needle, strong magnet (or wool/silk and hair), a small cork or foam slice, bowl of water.
- Stroke the needle in ONE direction along the magnet 30–50 times.
- Gently push the needle through the cork so it floats flat.
- Place the cork on still water and wait; it turns and holds a north-south line.
Why it happens: Stroke-aligning domains inside the steel turns it into a weak magnet; Earth's magnetic field then torques it around until it lines up. The needle points to magnetic north — not exactly true north, and that difference (declination) matters to navigators.
Yarn DNA extraction
You need: Fresh strawberry (or banana), zip bag, salt, water, dish soap, cold rubbing alcohol (chilled in a freezer), strainer, glass.
- Mash the fruit in the bag with your hands (2 min).
- Mix 1 tsp salt + 1 tsp soap + 3 tbsp water; pour in and mash 1 more min.
- Strain the juice into the glass. Tilt the glass and pour cold alcohol slowly down the side.
- Wait a minute: white stringy clumps appear at the boundary — DNA.
Why it happens: Soap and salt break cell and nucleus membranes and pull DNA out of its proteins; DNA does not dissolve in alcohol, so it crashes out as visible strands. You are looking at thousands of tangled molecules you inherited.
Shadow sundial
You need: Cardboard, a straw or pencil, a sunny spot, a marker, a clock to check against.
- Stick the straw in the centre of the card; put the card flat in sun.
- Mark the shadow tip and write the time every hour through the day.
- Do it again the next day at the same times — the marks match.
Why it happens: The Sun's apparent motion is Earth's rotation, about 15° an hour. Shadows trace that rotation faithfully, which is why sundials ruled timekeeping for thousands of years.
Elephant-free "elephant toothpaste" (kid-safe version)
You need: Empty bottle, warm water, yeast (a teaspoon), 3% hydrogen peroxide (the mild brown-bottle kind), dish soap, tray, safety glasses.
- Mix half a cup of 3% peroxide with a squirt of soap in the bottle; add a few drops of colour if you like.
- Add the yeast (pre-mixed with a spoon of warm water) and set the bottle on the tray.
- Watch the foam rope grow for a minute — then the yeast mixture can be poured down the sink with lots of water.
Why it happens: Yeast produces catalase, an enzyme that strips oxygen off peroxide at high speed. Released oxygen gets trapped in the soap as foam and warm to the touch (the reaction gives off heat). Never use hair-dressing peroxide for this.
The egg in two glasses
You need: Two glasses, water, 6 tbsp salt, two raw eggs (adult handles eggs), spoon.
- Fill both glasses with water; stir salt into one until it dissolves.
- Gently lower an egg into each: one sinks, one floats.
- Carefully pour the salty glass into the plain glass — the egg now hangs in the middle.
Why it happens: Salt water is denser than an egg, plain water less dense — so buoyancy flips. Layered liquids create a density staircase, the same effect that lets you float effortlessly in the Dead Sea.