Fredster1765

This question might seem strange or dumb.. At least it does in my mind, however I phrase it..
Anyway, I'm wondering about the reasons for acceleration being felt and constant velocity not being felt by a human body or other object. If you're sitting in a train or a car and it accelerates rapidly to 100 mph, a bottle might tip over, whereas if you're moving at constant velocity 100 mph, it won't. What exactly is the process by which the energy of that acceleration is felt by any object inside the car or train?

I should note that I don't study physics of any kind, so I won't be familiar with any mathematical formulae that might explain this!