The Science of Everyday Things
Everyday questions about toast, water, soap, warmth and the blue sky.
A slice of bread comes out of the toaster with a new aroma. A glass of iced water grows droplets on the outside. A spoon warms all the way to its handle. Ordinary objects keep giving us evidence that something is happening beyond what we can see.
Why does water conduct electricity? Why does a wet towel dry at room temperature? Why can tile and carpet feel different when they are equally warm? These twenty-one questions begin with familiar experiences and follow the chemistry, physics and biology behind them, from the kitchen and bathroom to the light overhead.
In the kitchen
How ingredients develop flavor, change texture and hold together.
- Why does toast taste different from bread? , Heating lets certain sugars react with amino groups in bread, producing new aroma and flavor compounds. This branching chemistry is known as the Maillard reaction.
- Why does sugar turn brown when heated? , Heat can break down and rearrange sugar molecules, creating new substances with brown colors and different flavors. This chemical transformation is caramelization.
- Why does egg white turn solid when cooked? , Heat changes the shapes of proteins in egg white. They can then join into a network that holds water, turning the runny liquid into a gel.
- Why does mayonnaise stay mixed? , Mayonnaise contains tiny oil droplets dispersed in a watery phase. Substances in egg yolk help stabilize the droplets, slowing their tendency to merge and separate.
- Why does bread dough rise? , In yeast dough, fermentation produces carbon dioxide. Gas held within the dough expands it before baking; in sourdough, acid-producing bacteria also help shape the result.
Water at work
Follow water as it escapes, condenses, bubbles and climbs.
- How can a wet towel dry at room temperature? , Water molecules can escape from a liquid's surface into the air even below boiling temperature. This surface process is evaporation, and it can cool what remains.
- Why does a cold glass get wet on the outside? , Water vapor already in the air can turn into liquid on the cold surface. The droplets usually come from the surrounding air, rather than passing through the glass.
- Why doesn't boiling water keep getting hotter? , During steady boiling at a fixed pressure, added heat mainly turns liquid water into vapor. The boiling temperature itself depends on pressure, so it is not always 100 °C.
- Why are small water drops round? , Surface tension favors a smaller liquid surface. For a given volume, a sphere has the least surface area, though gravity and contact with other materials can change the shape.
- How does a paper towel pull water upward? , Water wets the paper's fibers and moves through the narrow spaces between them. Surface tension and interactions with those fibers produce capillary action, which can lift water against gravity.
- Why does water conduct electricity? , Ordinary water contains dissolved ions: electrically charged particles that can move through the liquid. Their movement carries electric current. Highly purified water conducts electricity very poorly.
Around the house
The chemistry and electric forces behind washing, deposits and changing surfaces.
- Why does sugar stop dissolving in tea? , At a given temperature, a fixed amount of water can hold only so much dissolved sugar at equilibrium. Once the solution is saturated, extra sugar can remain as crystals.
- How does soap remove grease? , Soap molecules have regions that interact differently with water and grease. This structure helps loosen and disperse oily material so that rinsing can carry it away.
- Why does a kettle develop a white crust? , Heating hard water can cause dissolved substances to form solid calcium carbonate deposits. Water can look completely clear before those mineral deposits appear.
- Why can scratched paint lead to rust? , A scratch exposes iron to water and oxygen. Electrochemical reactions then transform some of the metal into rust.
- Why does a rubbed balloon attract paper? , Rubbing can leave a balloon electrically charged. Its charge slightly shifts the distribution of charges in nearby neutral paper, allowing attraction to outweigh repulsion.
Light and heat
How energy travels, and why appearances and touch can mislead us.
- Why does tile feel colder than carpet? , Tile can take heat from your skin faster than carpet does, even when both have the same temperature. Your sense of cold reflects the rate of heat transfer as well as temperature.
- Why does warm water rise in a pot? , Water warmed near the bottom of a cooking pot can become less dense than the cooler water above. Buoyancy makes it rise, setting up circulation that carries heat.
- How can a fire warm you without touching you? , A fire emits electromagnetic radiation that your skin can absorb. This transfers energy across the space between you and the fire without requiring hot air to carry it.
- Why can glass almost disappear in oil? , If a glass object and its surrounding oil have closely matched refractive indices, light changes direction very little at their boundary. That removes an important visual clue to the glass's outline.
- Why is the sky blue? , Molecules in the atmosphere scatter shorter visible wavelengths more strongly than longer ones. This sends blue light toward us from across the sky; our eyes' sensitivity also shapes the color we see.