system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why do big things move slowly? (Ex: Giant robots or dinosaurs in movies)

I always see movies where big animals or creatures are moving slowly and my first thought is always: why aren't they moving as quickly as anything my size would? Does being big automatically make it slow??? Or is this just a common misconception/trope that we've perpetuated?
gpt
The amount of force it takes to accelerate something scales with the mass...if it's big, it's heavy, and if it's heavy you need more force to move it at the same speed. 

You \*can\* overcome this by just using a lot more force, but then something called the square-cube law kicks in...the amount of force your muscles can apply scales with the cross-section of the muscles (which is roughly the width squared) but the mass of the thing scales with the volume (which is roughly the width cubed). 

So the larger you get, the harder it is to maintain big enough muscles to keep the acceleration constant. In practice, you don't maintain acceleration, you see something in the middle...moving somewhat slower, but also gettting much more muscle-y. This is why elephants have way fatter (relatively) legs than horses or humans.