But you already know about this, because F_g is what normies call an object’s “weight,” and for a given volume, weight depends only on the density. Now, if you dropped these blocks in a lake, obviously the styrofoam would float and the steel would sink. So clearly it has something to do with density.

What if you had a block of water with the same volume? If you could somehow hold this cube of water, it would feel pretty heavy, about 62.4 pounds. Now, if you place it carefully in a lake, will it sink or bob on the surface like styrofoam? Neither, right? It’s just going to sit there.

Since it doesn’t move up or down, the total force on the block of water must be zero. That means there has to be a force counteracting gravity by pushing up with equal strength. We call this buoyancy, and for any object, the buoyancy force is equal to the weight of the water it displaces.

So let’s think about this. The steel block displaces the same amount of water, so it has the same upward-pushing buoyancy force as the block of water. But because it’s denser and has more mass, down it goes.

In general, an object will sink if the gravitational force exceeds the buoyancy force, and it will float if the buoyancy force exceeds the gravitational force. Another way of saying that is, an object will sink if it’s denser than water and it will float if it’s less dense.

And right in the middle an object will neither sink nor rise to the surface—we call that neutral buoyancy. Humans are pretty close to neutral because our bodies are 60 percent water. That’s why you feel weightless underwater—the buoyancy force pretty much offsets the gravitational force.

Avast! Hold on there, matey. Aircraft carriers are made of steel and weigh 100,000 tons, so why do they float? Can you guess? It’s because of their shape. Unlike a block of steel, a ship’s hull is hollow and filled with air, so it has a large volume relative to its weight.

But what if you start filling it with cargo? The ship gets heavier, which means it must displace more water to reach that equilibrium point. In general, when you launch a boat or ship into the water, it’ll sink down until the weight of the water it pushes aside equals the boat’s total weight.

When I reviewed the GR III, I wrote about how much I liked snap focus mode, which allows you to set a predetermined focus distance regardless of the aperture. I set up my GR III to use autofocus when I half-pressed the shutter and snap when I quickly pressed, so that snap focus fired off the shot at my predetermined focus distance (usually 1.5 meters).

All that remains, but there is also now a dedicated letter, Sn, on the mode dial that sets the camera in Snap Focus mode, which allows you to dial in not only the distance you want focus at, but also the aperture you want to lock in. You can control the depth of field as well. I rather enjoyed this new mode and found myself shooting with it quite a bit.

Should You Get One?

The GR IV debuted at $1,497, which is significantly more than the GR III’s $999 price at launch. Is it worth the extra money? If you have a GR III and are frustrated by the autofocus, I think you will like the upgrade. It’s significant and, if you have the money, well worth it.

If you have any desire to use your pocket camera for video, this is not the one for you. See our guides to pocket cameras and the best travel cameras for some better, hybrid photo- and video-capable cameras. If you want an APS-C sensor that legitimately fits in your pocket, offers amazing one-handed control, and produces excellent images, the the Ricoh GR IV is for you.

Personally, I am holding out for the GR IVx, which will hopefully, like the GR IIIx, be the same camera with a 40mm-equivalent lens. At the time of writing, Ricoh would not comment on whether there will be a GR IVx.

I spoke with Raj Mills, Sleep Number’s senior vice President of partnerships and research. She tells me, “Our AI models take into account foam depth and still maintain the same level of accuracy regardless of how far below the surface of the bed the sensors are.” She shares that they are cohesively performing a ballistocardiograph, which monitors the blood flow generated by the heart and ultimately determines your heart rate score. How effectively they can do so is debatable.

Ultimately, I found there was quite a bit of variance in terms of the nightly score calculated on both ends. On good nights, both pointed to higher scores, but the final number could differ by up to 10 points. On the Sleep Number app, I found it concerning that most of the time, my Sleep Score numbers were not as high as I thought they would be—my average for the three-week test period was a 74.

Matrix Mattress

If you prefer a remote, that’s either a separate cost ($50) or potentially a different bed altogether. The only way to operate this mattress is by creating an account and downloading the app in advance. Security of one’s personal data is top of mind for many, and I wanted to know how the vast quantities of data accumulated by Sleep Number’s customer base were managed. When you first sign up for your account, you can either share your data with Sleep Number or opt out altogether. For those who share their data willingly—about 550,000 individuals, according to Mills—Sleep Number’s data science team performs research and presents findings from its consumer base at major sleep conferences, including SLEEP and World Sleep Congress.

It’s a comprehensive data set to work with, and it continues to evolve through the adaptive AI at play, which includes SleepIQ technology. According to Mills, the company’s AI models are structured to analyze sleepers at an individual level, because every sleeper has a different build, age, pain issues, and various needs. According to Sleep Number’s privacy policy, the company doesn’t sell your information to third parties, and you can withdraw your consent to share information at any time. At the end of the day, Sleep Number is a business that can potentially use your data to develop new products, and it’s up to you whether that’s worth it or not.

Power Couple

An adjustable base is what enables each side of the mattress to independently adjust head and foot angles. I tested the FlexFit 3 adjustable base alongside the P6 mattress, which is Sleep Number’s top-of-the-line offering. It offers timed foot warming (which takes about two minutes to heat up and has a two-hour default setting) to help blood flow away from your core and aid faster sleep. There is also a zero-gravity setting, partner snore (elevates the head and neck slightly to help open up airways), and motion-detect underbed lighting. I loved the gentle light source for late-night bathroom breaks, and the split king adjustability allowed me to partake in late-night reading without disturbing my partner. However, the only feature that separates the FlexFit 2 base from the FlexFit 3 is the inclusion of foot warming, and it’s a $400 upcharge for a queen size.

Photograph: Julia Forbes