demonstrations:sticky_rice_friction_lift
Sticky Rice Friction Lift
Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Force
Alternative titles: Friction in Packed Rice
Summary
By repeatedly inserting a knife into a container of rice, the grains gradually pack more tightly. This increases friction, eventually allowing the knife to lift the container filled with rice.
Procedure
- Fill a clean container (such as a glass jar or plastic bottle) almost to the top with uncooked long grain rice.
- Hold the container firmly with one hand.
- Push a blunt-bladed knife or pencil straight down into the rice.
- Pull the knife out slightly, then push it back in, repeating the process without fully removing the knife.
- Add more rice if the level drops as the grains settle.
- Continue inserting and removing the knife until the rice becomes tightly packed and resists movement.
- Test if the knife can lift the entire container by pulling upward gently.
Links
Impossible Rice Lift? - learningscienceisfun:
Can you lift a bottle of rice with a PENCIL? 🍚✏️ | Friction experiment | Wonderlab+:
📄 STICKY RICE - BBC one: https://downloads.bbc.co.uk/bang/handson/sticky_rice.pdf
Variations
- Try different types of rice (short grain, sticky rice, basmati) to see which packs most effectively.
- Use a narrow-necked plastic bottle and a skewer instead of a jar and knife.
- Experiment with other granular materials like sand, lentils, or beans.
Safety Precautions
- Adult supervision required.
- Handle the glass jar carefully to avoid breakage.
- Use a blunt knife to prevent cuts.
- Do not force the knife too hard to avoid injury or breaking the container.
Questions to Consider
- Why does the rice become more compact the more the knife is pushed in and out? (The grains shift into empty spaces, reducing gaps until they are tightly packed.)
- What role does friction play in allowing the knife to lift the container? (The compact grains press against the knife blade, creating friction strong enough to support the jar.)
- Would this work with liquids instead of rice? (No, liquids cannot be compacted to increase friction in the same way as solid grains.)
- How might the size and shape of the grains affect the result? (Smaller or stickier grains may pack more tightly and increase friction faster.)