5 Mechanically Extraordinary Everyday Objects

The tools that make it possible to perform routine tasks like ironing wrinkles or steaming a pot of rice have become ubiquitous to daily life. But the insides of these ordinary objects can reveal extraordinary mechanical designs, from temperature-sensitive magnetic systems to elaborate planetary gear boxes. 

And while the day-to-day activities have come to rely on a seemingly endless number of mechanically fascinating objects—like the ones featured in fabricator Mike Warren’s “Cut in Half” channel on YouTube—these five are worthy of a closer look.
 

Rice cooker

Fluffy grains of rice are the result of striking just the right balance between water and heat.

Rice cookers take the guess work out of finding that sweet spot and it’s all because of a clever mechanical design that relies on simple physics. 


That’s why Daniel Preston, assistant professor of mechanical engineering at Rice University, cited the rice cooker as one of the more mechanically interesting objects of everyday life.

“It’s a very elegant mechanism that perfectly cooks the rice every time you use it,” Preston said.

Inside the appliance is a temperature-sensitive magnet that triggers a spring-loaded lever. 

Once the rice cooker is switched on, the switch is held down by a magnet in the center of a heating plate that touches the bottom of the inner rice pot. The plate heats the rice until it reaches 100 °C. 

The boiling point for the water in which the rice is cooked is just below the temperature, known as the Curie point, above which certain materials lose their magnetic properties.

“The magnetic mechanism is perfectly tuned so that when it gets a bit above 100 °C, corresponding to the water being fully absorbed by the rice or evaporated, it loses its magnetic attraction and ends the cooking cycle,” Preston explained.

With the heating plate temporarily without its magnetic attraction, the plate releases its connection to the spring, and the rice stops cooking. 
 

Laptop



Discussions about the inner workings of a laptop often focus on hardware such as the central processing unit and motherboard that function as the brains and nervous system of the device.

But if these vital pieces get too hot, the computer will slow itself down and, in extreme cases, may shut itself off to prevent damage. Also important, Preston said, are the mechanical components that make up a laptop’s cooling system and are essential to keeping the device from overheating.

The system consists of a fan that moves air over a heat sink, a copper heat pipe that carries heat away from the CPU, and thermal paste that ensures the transfer of heat. 

“It’s a really cool system that uses the phase change of a working fluid within the heat pipe to passively move heat from the processor to a heat sink, where a fan rejects that heat to the surrounding air,” Preston added.

As the CPU generates heat, the heat is transferred to the enclosed pipe, causing fluid inside the pipe to boil and evaporate.

The expansion of this vapor creates pressure that drives the flow of the vapor to the opposite, cooler end of the heat pipe, where the fan blows ambient air across the pipe’s surface.

This process removes excess heat, and the vapor in the heat pipe recondenses into a liquid that flows back through the pipe, where it picks up more heat and repeats the cycle. 

“This phase-change process is in essentially all the laptops we interact with, and a lot of other electronic devices, including the newest line of iPhones,” Preston said.
 

Power drill

Anyone who’s ever spent hours manually turning screws knows that for big projects, a power drill is the ideal tool for the job.
And anyone who’s ever seen the intricate insides of a power drill can understand why.


As Preston explained, drills rely on a highly efficient internal motor and a complex series of nested gears in order for drill bits to spin at high and variable speeds. By using magnets and electric currents, the motor is able to convert electrical energy into mechanical energy. 

Squeezing the drill’s trigger activates an electric current that turns on the motor. The current then flows through wire coils inside the motor, while electricity passing through a wire creates a temporary magnetic field that interacts with other coils inside the motor. As opposite magnetic poles attract and like poles repel, these magnetic forces create a push-pull of forces that cause the inner motor to spin.  

Because the motor is powered by electricity, it spins at very high speeds but lacks the turning force, or torque, necessary for drilling.

This is where the gear system spins into action.

Power drills use what’s known as a “planetary” gear system, consisting of a central “sun” gear that turns multiple smaller “planet” gears inside an outer “ring” gear to distribute the mechanical load.  


“The gearbox involved in the system steps down the speed of the drill bit and, at the same time, steps up the torque, which allows you to do useful things like drive a screw into a wall or into furniture,” Preston explained. 
 

Clothing iron

Electric irons offer a simple solution to smoothing out the wrinkles on your favorite shirt. But the inside of a clothing iron contains a complex mini-machine consisting of a coiled resistive heating element, electrical wiring, a bimetallic strip to regulate temperature, and gravity-fed valves, along with a small water tank and thick metal plate.



“The clothing iron is interesting because a lot of the ones you interact with these days also have a steam feature. And so, the clothing iron has to maintain a set temperature point, and it typically does that with some sort of feedback control,” Preston said. 

When plugged in, the iron converts electricity into heat by using the internal resistance coil. As the coil generates heat, the heat transfers to the metal plate on the bottom of the iron.

As the heating process continues, a bimetallic strip inside the device bends and pushes a separate spring to open or close the electrical circuit and regulate the temperature. 

The dial on the iron can be adjusted to change the temperature at which the bimetallic strip opens the circuit. 

For irons with a steam feature, the heat raises the temperature of the water as it drips from the internal tank into a hot steam chamber above the plate. The steam then escapes through tiny holes in the metal plate. 
 

Foam dart blaster

Generations of backyard battles have been waged by kids (and adults) taking aim at one another with projectile foam darts. Their weapon of choice is the spring-loaded foam dart blaster, an iconic vestige of outdoor play that, as Preston explained, is made possible by spring-powered mechanical energy.

“You put in the energy at the beginning with the cocking mechanism, and you release it later when you squeeze the trigger,” Preston said.

Inside of the blaster is a metal spring that stores energy when squeezed, and a plastic plunger that fits tightly inside of a tube connected to a cocking mechanism. 
 
When the blaster is cocked, a small piece of plastic, known as a catch, locks into the plunger, pulling it back and causing the spring to compress and store energy. 

Pulling the trigger moves the catch out of the way, releasing the plunger and allowing the compressed spring to snap back and force out high-pressure air to propel the dart. 

“That’s what pushes the dart out and shoots it across the room at whomever you’re playing with,” Preston said.


Autumn Cafiero Giusti is an independent writer in New Orleans.