If I drive my car through a corner slowly I’ll be fine. If I go fast, the car will skid off the road. All the materials are the same, the execution is the same. The only difference is over what amount of time this happens? The example is not important, the same goes for pretty much anything. Filling a bottle, ripping a sheet of paper..
I understand this from a intuitive perspective, but I wonder if someone can explain why time matters in physics in a simple way. What is the fundamental difference between doing something fast vs. slow.
I’m sure this is a silly question if you know some thermal dynamics or special relativity, but remember, I’m only 5!
In: Physics
Look the other way around.
TIME IS THE RESULT:
You want to do a turn in half time, you need twice the force.
You wanna get somewhere in less time, you need to go faster.
You wanna oxidate petrol in a long time? Leave your tank sitting there for 6 years with a little vent, and it will become mostly water and CO2, you wanna oxidate the same petrol fast? Set it on fire.
The difference in those situations is not the time itself, but how quickly you are doing those things. Speed CAN and WILL affect the outcomes of situations (for example, the car must slow down much more than it has to if it is moving at a slower velocity) such as the ones you’ve listed. The time the action takes is because of the speed in which it is happening, not the other way around.
>If I drive my car through a corner slowly I’ll be fine. If I go fast, the car will skid off the road. All the materials are the same, the execution is the same. The only difference is over what amount of time this happens?
You have 2 things going on here. First is your velocity, and then there is your “turning rate”. Velocity depends of time and, your turning rate depends on your acelerattion, which is a unit dependant of time. In this example you are making your velocity faster while your turning rate is the same, so the combination of both is different.
A good example would be: I move 1 m/s forward and 1 m/s to the left. Why if I move 1 second forward at 2 m/s but at 1 m/s to the left it’s different? Because in 1 second I moved 2 meters forward an 1 to the left. You should move to the left 2 m/s too and it would be the same.
Why is it importants in physics overall? Physics study both the way some things change and how some things stay the same. For studying things that change, you need to compare them in different moments (time). In real life a lot of stuff depends on time, so just the way you can’t expect to move faster forwards and with the same speed to the left being the same thing as moving at the same speed to both directions, you can’t expect things to be the same if you change the speed you have moving or doing something.
If I want to run too fast, there is a point that I would damage myself (Just like falling from the sky). Is not because of my speed but my speed compared to the speed of the particles in my body adjusting, that are limited by the forces between themselves (Force depends on time too).
Your larger question about time in general is rather complicated but I’ll focus on the specific situation you mention. Basically when you go faster you are or have added more energy to create higher momentum ,which is mass and velocity moving in a direction. Objects tend to move in straight lines so it takes more work and friction etc to prevent that mass continuing in a straight line than if you had added less energy. ( I hope)
Energy matters more than time. So if I want to move from where I am to a mile down the road, I can walk. It will take maybe 15 minutes, but I won’t be very tired. I could run, and get there sooner, but I’ll probably be out of breath. Or if I wanted to get there even faster, I could strap a rocket on my back and Wile E. Coyote my way over there, but then all that energy has to go somewhere, and my landing won’t be pleasant. The same thing has happened (traveling down the road), but the energy used is way different. All that energy has to come from somewhere, and has to end up somewhere, because it can’t be destroyed.
So back to your example of going around a turn. The actual turning takes some amount of energy. If we use just enough energy, we’ll make the turn and go on our merry way. If we use too much (by going too fast), all that extra energy has to go somewhere. It ends up going into momentum (which makes things keep going in one direction) and skidding tires and bad times.
It’s not the time, it’s the energy.
Time is just a basis of measurement. It may seem like the amount of time for you to take that corner is what made you skid off the road, but it’s really the force–in this case inertia–that made you crash.
But how we calculate and measure these things is based off time (how long it takes to get from A to B) because it’s a constant, at least to a certain degree. You can rip a piece of paper fast or slow, but really it’s how much force you are using. The problem is you can’t look at that happening and calculate the force. But less force takes more time and we can use that time to calculate the force.
This is not a silly question. But I don’t think you’re going to find a satisfying answer in the way that you want. There are some things that physics takes as basic facts of existence. Space, time, energy, etc. The laws of physics start by accepting that these things matter, and then use these concepts to describe and explain other things. Physics is more about answering questions like “How do things change with time?” than questions like “Why does time even matter in the first place?”.
[Relevant quote](https://www.lesswrong.com/posts/W9rJv26sxs4g2B9bL/transcript-richard-feynman-on-why-questions) from Richard Feynman on magnetism: “And when you explain a why, you have to be in some framework that you allow something to be true. Otherwise, you’re perpetually asking why. … But it’s a force which is present all the time and very common and is a basic force of almost – I mean, I could go a little further back if I went more technical – but on an early level I’ve just got to tell you that’s going to be one of the things you’ll just have to take as an element of the world: the existence of magnetic repulsion, or electrical attraction, magnetic attraction.”
I would add time to this list of things that physics just accepts as true as an element of the world. There is no “why” answer for why time matters in the way that I think you’re looking for. With that said, there are interesting scientific debates about time in physics. Time often plays different roles in different theories of physics. For example, the role of time in quantum mechanics is not quite the same as the role of time in relativity. There are some good essays on this question [here](https://fqxi.org/community/essay/winners/2008.1). I also liked the book Time Reborn by Lee Smolin, in case that helps. This [page](https://en.m.wikipedia.org/wiki/Problem_of_time) might also be interesting.
So seeing some other responses and you’re follow-ups to those, I think (but correct me if I’m wrong), that in distilling your question down to its simplest form, what you’re really asking is “why does time exist,” which is really another way of asking “why is the universe the way that it is.” Unfortunately, the answer to these kinds of questions is always we don’t know and it’s not a particularly useful question to ask because it doesn’t tell us anything. Things in the universe are time-dependent because time exists. That’s the best answer you can get.
> Filling a bottle
Fluid mechanics tends to be highly “nonlinear”, meaning that straightforward changes in the system can have very complicated impacts on how it behaves. For example using a larger or smaller bottle or pouring it more quickly or slowly can result in a completely different kind of flow. In particular there is a distinction between “laminar” flow in which the fluid flows in a smooth, orderly way, and “turbulent” flow in which it’s more random and chaotic. Generally if you pour liquid very slowly you will get laminar flow, and if you gradually increase the speed you will eventually hit a threshold at which it becomes turbulent (the threshold doesn’t depend purely on the speed – other factors are involved too such as how viscous the fluid is). You’ve probably come across that effect when pouring liquids out of bottles.
Accelerations are changes in velocities over time. When you turn, for instance, an acceleration is needed in the direction you are turning. This acceleration is bigger the quicker the movement is, and it’s caused by the friction, or grip, of the tires with the ground. If you do the movement too fast, the acceleration needed might exceed what the friction can provide, given that the friction is not dependent on time. If the turning is slow, the friction is more than enough to give the acceleration needed. For other examples, you have to find out what variables are time dependent, like viscosity, and they would explain the variation in behavior between quick and slow versions of the same movement.
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