Is hitting an obstacle half the size of my scooter wheel the same as hitting an obstacle half the size of my bike wheel? I rode a scooter (the kind that you stand up and hold on to, with small wheels) and it didn't seem to handle bumps that would be minor if I was riding my bike. I was wondering if that is because hitting an obstacle half the size (height) of my scooter wheel would be like hitting an obstacle half the size of my bike wheel if I was riding my bike. If so, it makes sense why a small obstacle on a scooter is more dangerous because hitting an obstacle half the size of my bike wheel would be a huge obstacle on my bike and definitely knock me over. Is my intuition correct? This would seem to indicate scooters are much more dangerous than bikes, all else being equal.
Thank you!
 A: 'All else being equal' there are two main differences between hitting something on your bicycle and on your scooter.
You are correct in identifying that the relative dimensions of the two wheels will be a factor. If the bump is much smaller than the wheel in each case, there won't be a significant deceleration. But as the bump gets bigger it will have more 'stopping power' - to the point that when the bump is precisely the same height as teh radius of the wheel it will stop ot completely.

But there is also a second effect - on the scooter, your centre of mass is much higher (relative to teh wheel axle) than on your bicycle. So if your bike tries to stop relatively suddenly you can (to some extent) brace yourself against the handle-bars and won't go over the top of the bike. But on the scooter your CoM is way higher and the handle-bars won't help at all in stoping your body flying over the wheel. If you buiklt a bicycle in which your CoM was equivalently far above the wheel, you bike would become similarly unstable when hitting a small obstacle.

