Loose Ends of Curiosity
Questions readers keep asking, with answers short enough to remember.
Objects and materials
Why does my fridge door resist being reopened?
Room air entered while the door was open. Once shut, the fridge cools it and its pressure drops, so the outside air presses the door against its seal. A second or two later, air seeps back in and the door opens normally. See the full puzzle.
Why does a tape measure hook wobble?
It moves by exactly its own thickness, so the reading is right whether you hook it over an edge or press it into a corner. More on tape measures.
Is cornflour and water a liquid or a solid?
Both, depending on speed. It's a shear-thickening fluid: grains slide under gentle stress and jam under sudden stress. Read about oobleck.
Why are soap bubbles round?
Surface tension pulls the film to the smallest area that can enclose its air, and for a fixed volume that is a sphere. Inside a wire frame, the same rule produces flat films meeting at 120 degrees.
Why does ice from the freezer stick to dry fingers?
Freezer ice can be well below 0 °C. The thin layer of moisture on your skin freezes on contact, briefly gluing you to the cube. Warm water releases it gently; pulling does not.
Why does a metal spoon in tea heat up faster than a mug handle?
Metals contain free electrons that carry heat energy quickly, so they conduct far better than ceramic. Both may reach similar temperatures eventually; the spoon simply gets there first and delivers heat to your fingers faster.
About this site
Are the demonstrations safe for children?
We pick low-risk activities using common household items and avoid heat, sharp tools and strong chemicals. An adult should lead, and every page includes safety notes. See the demonstrations.
Do you publish sponsored content?
No. We don't accept payment for coverage, product placement or links.
How do you check your facts?
We work from textbooks, patent records, museum collections and published research, and we prefer dates and names we can trace. If we get something wrong, we correct it and note the change. Our method.
Can I suggest an object for you to explain?
Please do. Use the observation console on our contact page.