why do giants in shows and movies always look like they’re moving so slow?
In: Physics
Because in the real world, small animals tend to move quickly relative to their body size, and big animals tend to move slowly.
Think of a mouse or insect. It can scurry about very quickly, moving at way more body lengths per second than us, or than other, larger animals. Consider an elephant, for instance. It is large and lumbering and its movements are slower relative to its size.
Let’s look at some numbers to make this more concrete. Usain Bolt has a top speed of about 12 m/s, or well over six body lengths per second. A house mouse can run at over 3 m/s, but its body is less than 10 cm long, so it can do more than 30 body lengths per second. That’s faster (by this measure) than a cheetah, which tops out at a measly 16 body lengths per second. An elephant has a top speed of about 11 m/s, relative to an average body length of about 4 m, so it can do about 2.5 body lengths per second.
So, elephants are about as fast as humans (at top speed), but look a lot slower while doing it. Mice are slower than us but look faster. And it’s all in these numbers of speed relative to size.
Giants, if they existed, would be no different. They might outrun the fastest humans, but relative to their body size they would look slower. E.g. maybe your giant stands 10 m tall and runs at 20 m/s, which is way faster than a human. But, that giant still does only two body lengths per second, compared to our six. She will also be taking fewer, though larger steps. So, all in all, her movement looks a lot slower than those of a human running at top speed.
The reason why bigger animals get slower compared to their body size has to do with [square-cube law](https://en.wikipedia.org/wiki/Square%E2%80%93cube_law)s that govern biomechanics. For instance, if you scale up an animal by a certain factor, its weight will increase with the cube of that factor, while its muscle cross-section (which governs its muscle strength) increases more slowly, with the square of the scaling factor (e.g. if you double the size, the animal’s weight increases eight-fold while the muscle cross section only quadruples). This makes it harder for animals with larger bodies to apply the same force per weight to their limbs as a smaller animal (they could grow larger muscles to compensate, but only to a point). Their muscles and limbs are still bigger so they can put out more power and be faster on the whole, but relative to their bodies big animals tend to be weaker (and slower).
(Of course this is only a general principle, and there is lots of variation between animals of the same size, depending on whether they evolved to prioritize speed.)
Latest Answers