Household machines

Your kitchen and bathroom are full of machines you use every day without giving them a second thought. Yet each one contains a genuinely clever idea: the washing machine works through a complete program with sensors, the fridge pumps heat even though it is supposed to be cold, and the microwave makes water molecules rotate. Time to take these three boxes apart, at least in our heads.

The washing machine: a program with senses

At its core a washing machine is an automaton working through a fixed sequence of steps: let water in, heat, tumble, pump out, rinse, spin. It has the right tool for every step. A valve opens and closes the water inlet, a heating element warms the water, a motor turns the drum, a pump moves the water out. The exciting part is the sensors in between: a pressure sensor measures the water level, a temperature sensor reports when the water has reached the 40 degrees Celsius you selected. So the controller does not switch blindly by time, it waits until the sensor gives the green light. That is why the same load sometimes takes longer and sometimes less.

The fridge: a heat pump

Now for perhaps the biggest aha moment in the kitchen: a fridge does not produce cold, physically there is no such thing. It transports heat from the inside to the outside. To do this, a refrigerant circulates in its pipes, a fluid that evaporates at a very low temperature. Inside, the evaporating refrigerant absorbs heat from the food compartment, just like evaporating sweat cools your skin. A compressor then squeezes the vapour together, making it hot, and at the coils on the back, or in the side walls on newer models, it releases the heat into the kitchen. Touch the fridge there, it is warm. That is the heat that used to be in your yoghurt.

The microwave: making water jiggle

The microwave heats in a completely different way from a stove. Inside it sits a component called a magnetron, which produces electromagnetic waves at about 2.45 gigahertz. Electrically speaking, water molecules are tiny dumbbells with a slightly positive and a slightly negative end. The rapidly alternating field of the microwaves tugs at these dumbbells and makes them jiggle back and forth billions of times per second. This jiggling is nothing other than heat, and it appears directly inside the food instead of in a hot plate first. That is why the plate often stays lukewarm, it contains hardly any water and is mostly warmed by the hot food.

One pattern for all machines

As different as the three appliances are, they follow the same pattern: sensors measure, a controller decides, actuators like motors, valves or heaters carry it out. The washing machine measures water level and temperature, the fridge measures the inside temperature and switches the compressor on and off, the microwave counts down the time and controls the magnetron. Once you know this pattern, you will spot it everywhere, from the toaster to the dishwasher.