Viewing a single comment thread. View all comments

mutandis57 t1_jazlfrt wrote

This is exactly why Newton's laws were revolutionary and why it took humanity until 1687 to discover them! Until then, it was perfectly reasonable to believe everything naturally slows down and stops, unless someone is working hard to keep it moving. That's because everything we could see around us did just that! We know now that everything that we see slowing down does so because of friction and air resistance, but it was not obvious if you've never seen anything different. It took Galileo's physics experiments with carefully constructed artificial conditions to inspire an alternate explanation.

Maybe the closest everyday example of a self-moving object they had at the time was a runaway horse cart. Later on it was an easier idea to swallow when we had trains around. Trains have such low friction that you have to work hard to slow them down. It's more natural to believe that an object in motion remains in motion if you've seen trains your whole life!

2

KWOOOSH OP t1_jazssww wrote

But what keeps the train moving? I know the answer to this question is inertia, but intuitively it makes sense that there must be some force that is making the object continue to move, even at a constant velocity. I guess a better question is do we know why objects with no net force can remain in motion? Like, it makes sense to me that when net force = 0 = no net movement, but not the constant velocity part.

0

call_me_mahdi t1_jb0zanx wrote

I read almost all your replies Kwooosh, the keyword you are using is "intuitively". The problem is that since we lived our whole life on earth where friction happens all the time this make sense for this topic to feel counter-intuitive. Newton law is a mathematical model and it could be counter-intuitive sometimes.

6

Coomb t1_jb17zvk wrote

>But what keeps the train moving? I know the answer to this question is inertia, but intuitively it makes sense that there must be some force that is making the object continue to move, even at a constant velocity. I guess a better question is do we know why objects with no net force can remain in motion? Like, it makes sense to me that when net force = 0 = no net movement, but not the constant velocity part.

Why is it that when you're standing inside a train (or airplane or car) moving at constant speed, you move along with the train without having to constantly horizontally push on the floor?

According to your reasoning, you're moving at constant velocity and that means you need to be pushing on something to keep moving forward. But actually you don't have to push on anything. Does that tell you anything about your intuition with respect to motion in different frames of reference?

You may also want to contrast this experience with your experience on something like a merry-go-round, where you know that unless you are actively exerting force against a pole or something else on the merry-go-round, you'll fall off. Do you know what the key difference between these situations is?

2