Science In Real Life

“Misguided Intuition” at first sounds less like a subject for a science essay than it does a name for that new indie rock band everyone’s talking about. But as it turns out, the human brain comes hardwired with certain perceptual biases, and many of those have to do with how we interpret the physical world around us. But the reality is much more subtle than it seems. Every day we see objects moving at velocities, subject to forces, and experiencing acceleration, but the dynamic between them is so intricate that its true nature can nevertheless remain elusive.

A common example of this kind of errant physical instinct is confusion between acceleration and velocity. Try this experiment the next time you’ve got the highway to yourself: first accelerate smoothly to 80 mph. Then accelerate past it to 90, hold it there for a moment, and decelerate back to 80. Your brain, or more precisely your inner ear, will be telling you that your second 80 is slower than your first 80. Why? Because your inner ear senses acceleration, not velocity. (Disclaimer: Science In Real Life is not responsible for any speeding tickets that may result from this experiment. Informing the police officer that you were Speeding For Science is not likely to help your situation.)

Another instance, possibly even more frequently observed, is that velocity is relative. Am I moving away from you, or are you moving away from me? Physics doesn’t care. Physics works the same either way. Physics is indifferent to your disorientation. So when you’re sitting on a train in the station and you can’t tell whether your train or the one next to you is the one that’s moving, just remind yourself that it doesn’t matter.

Unless what you’re interested in is which one is moving relative to the train station. That one does have an answer, and it’s almost always not yours.

Next we come to fictitious forces, which apart from being one indefinite article away from a fantastic band name, is another one of those areas where our persistent human intuition gets in the way of appreciating what’s really going on. And it’s another mostly experienced in a moving vehicle. (Side note: Theories of physics have scales, or regions where they operate best, like a politician in her home state. The flawed physics we all have in our brains operates fine when you don’t go faster than a human can run. Go much faster, like in a car, and brain-physics yields the floor to Newtonian mechanics.)

Okay, you’re in the passenger seat of a car. The car takes a sharp turn going too fast, and somewhere in the back of your mind right next to the thoughts about how you should be the one driving, is the sensation that something is pushing you out, away from the turn. That’s centrifugal force, the most popular fictitious force. The name comes from the fact that physicists like it when the laws of physics are the same no matter who is using them. Centrifugal force only shows up when you’re adding things up from a rotating point of view, or reference frame. While you were taking that sharp turn, I was standing on the sidewalk, and what I saw was the car pushing you inwards – centripetal force. You had inertia going forward before the turn, and so the turning car exerted a force to change your direction.

What’s the big deal? One point of view is as good as any other, right? Well, while fictitious forces are mathematically valid, in the sense that calculations with them give the right answers, they are not beholden to Newton’s third law, F = ma, like real forces are. Instead, they began as faux-accelerations (created in the equations by the shift to a rotating perspective) and migrated over to the Force side. In other words, they are not a result of actual physical interactions.

Shifting gears a bit, we now have an example from thermodynamics. Normally when you touch something that feels hot, you jerk your hand back. You might identify the object aloud as being hot to someone nearby. Same thing on the other end – if something feels cold, we decide that it is cold. Seems reasonable, but our senses are lying to us with the persistence of a con artist. What your skin detects is not temperature but heat exchange. Something feels hot because heat, in the form of molecular motion, is moving from the object to your hand. Cold is heat leaving your body.

What’s the trick? The trick is that heat flow is not solely dependent on temperature. Different materials conduct heat at different rates, based on their internal structure. This is why you can grab a loaf of bread fresh out of the oven, but not the metal rack, even though they’re both at a toasty 425 degrees F. Metals are great heat conductors because their atoms share electrons like hippies share … well, lots of things. On the other end of the scale are substances like aerogel, which even under direct flame remains as cool as a whole produce section full of cucumbers.

So, to sum up: Misguided Intution, Speeding For Science, The Fictitious Forces, and Heat Conduction would all be excellent names for a band.