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
Because while the materials and execution are the same, the forces aren’t.
For example, a car turning a corner at 50mph has a lot more energy and inertia than a car turning at 5mph, and that a lot more energy to overcome the friction of the tires if you want the car to change direction.
Good answers but not really ELI5s. Here’s my shot at it:
Stuff happens, things change. Time is just a way of describing how those changes are connected.
Now, why does time matter in physics? Because time only goes one way. Lots of things can happen in different directions but not time. It only goes one way. It’s called the arrow of time. One way to know the direction of time is that over time, things break. If you drop a glass, it only shatters, never shards of glass reforming. Your room only gets messy, it never cleans itself. This is called entropy or the amount of order or disorder in a system. With time, things tend to become disordered, not the other way around.
Other people have addressed the question, so I’m just going to point this out which may help you understand it in the context you’ve presented the question:
A similar question you could ask is “Why does the width of the car matter?” Even at the same speed and same height, a skinny car tips over whereas a wide car is able to make the turn.
That might be something you can wrap your head around easier if you can visualize why that’s happening, and it may be a good stepping stone to understanding how time becomes relevant in that situation.
I think a good way to look at this is to remember that Newton’s physics, although very well conceived, are known now to be incorrect. They work at short distances, speeds, and gravitational influences, but when any of these things reach their extremes, Newtonian physics falls apart.
Einstein’s great leap of genius was to realize that time does not represent the *flow* of the universe; it represents the *shape* of the universe. In short, although it’s absolutely counterintuitive to humans, every single experiment that has ever tested any aspect of Einstein’s theories have shown them to be correct. Time isn’t what we intuitively think it is. Time as a *flow* is an illusion—an emergent property of experience, not a fundamental aspect of reality.
So as for why it matters, taking the fact that time is a dimension: it matters for the same reason that a photo of a statue and a statue are two different things. Add in one more dimension to the shape of a thing, and it’s a vastly different thing.
Time is of secondary issue here. You speak about speed which gives more momentum (kinetic energy) when combined with the mass of your vehicle.
There are a number of different ways you could approach this, but I would suggest that the most important is the relationship between energy and time. Energy is one of the most important concepts in physics and doing something fast or slow necessarily changes how much energy is involved. A car hitting a wall at 1 m/s vs 30 m/s produces very different results because the latter has 900x more energy involved and that energy needs to go somewhere. How this difference in energy manifests itself will depend on the context, but the fundamental difference between doing something fast or slow is how much energy is involved; and since fast and slow don’t make sense without the concept of time, energy and time are inherently related.
Most physics equations have time in them as a fundamental variable, which makes things more energetic.
There are some examples of going slower making things faster. The International Space Station goes slower than geostationary satellites, but it also completes a smaller orbit path due to that, so it goes around the planet every 90 minutes rather than every 24 hours.
Want to make a sharp turn in a plane or ship in a game? Drop the throttle while making the hard turn and it will complete faster because the turning circle becomes smaller.
Most, maybe all of physics is studying cause and effect, or the interaction between different types of phenomena. Without time those things don’t exist.
Another large part of physics is studying how different types of energy are transferred or transformed. A fundamental component of that is how much energy and how quickly, because that tends to affect the result. Whether you’re looking at the macro (object) or micro (molecular) level, the same amount of energy imparted over a longer vs shorter time can be the difference between the structure absorbing the energy vs the structure collapsing. There’s no deeper explanation for that other than that’s just how the universe behaves.
The relationship between time and the dynamics in turning a corner are not so linear, as you suggest.
Momentum is defined as mass x distance / time. If a given mass travels a given distance in time t, as t becomes small momentum becomes very big.
With a large momentum, a turn requires a large change in momentum. If you change your momentum in a time t, the force required is inversely proportional to t. That is, the faster you go, the smaller t is, and the larger the force is.
In a world where everything was perfectly rigid (cells in your body included), you most likely wouldn’t notice a difference between a fast and slow turn. However, literally everything which composes us and objects is made of atoms and molecules, which are held together through various forces. The larger the force applied, the easier it is for said force to deform or rip an object.
Summary:
Thank you all for all your comments and in depth explanations.
Since there are a lot of comments, I figured I’d try to summarize my impression after reading.
Now, bare in mind, this is just my “uneducated” impression, so I might have gotten some things wrong.
1. Some comments explain why a car going fast skids off the road. These are good explanations, but not really what I was seeking. This is my fault for not framing the question precisely enough, and I actually still don’t think I have the question fully formed for myself.
2. Many of the comments use explanations through inertia/speed/acceleration/force. These are also good explanations, but feel a bit circular to me as time is like such a basic ingredient in all of those.
3. The third category that makes the most sense to me is not an explanation, but a reference point that help me come to terms with the concept. ->Looking at time as a dimension rather than flow.. It is just another dimension to determine our “location” in 4D. The same as up/down/forwards/backwards. Several people introduced this, but I found rangeDSPs comment made it click for me, so go check that one out.
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