How Squirrels Survive Falls From Any Height

The video above (aside from being, in my opinion, very entertaining), talked about a lot of physics concepts that we've covered. For example, it talked about how squirrels use conservation of angular momentum to move through the air--they pull their limbs in closer to their body to rotate, and once their body is facing the direction they want, they straighten their legs to stop their rotation. This is very similar to the ice-skater example that we talked about in class, where decreasing the moment of inertia caused an increase in the angular velocity (and vice versa), via the conservation of angular momentum. I thought it was very interesting that something we use complex concepts and math to explain is something that animals like squirrels know intuitively, and can even use to their advantage. 

The most interesting part of this video was the narrator describing the safety of the squirrel obstacle course he built--some of the parts of the course were built to collapse if the squirrels stood on them for too long, or even (gently) throw the squirrel off of the obstacle. The narrator explains that this was actually very safe, because squirrels can survive a fall from any height. I hadn't known this! He even includes a short clip where a squirrel falls from a tall apartment complex (it's hard to tell in the video, but it looks like it is from at least the fourth floor of the building) and survives. As the narrator explains, squirrels can survive these falls because they can survive a fall from their terminal velocity--and they use physics to do it. For one, they always land on their feet, as cats do, because of their manipulation of angular momentum as discussed above. This video also shows how squirrels will flatten out in the air in order to increase the drag force. 

The equation of drag force from the Falling Bodies lab we had a few weeks ago shows how this flattening helps the squirrels: flattening out their bodies increases their cross-sectional area (A). Because we know that terminal velocity occurs when net force, and thus acceleration, is zero, the squirrels will reach terminal velocity when drag force is equal to the force of gravity. If the squirrels can manipulate A, then their velocity will be lower with the overall drag force remaining the same, meaning that they can reach net force of zero, and thus terminal velocity, at a lower velocity than they would if they did not change their cross-sectional area.  

So in conclusion, how squirrels are able to survive falls from any height: 

Their ability to move quickly in the air through conservation of angular momentum, manipulation of their cross-sectional area, and their low masses (the squirrels in this video were all between 500-800 g) keep their terminal velocity quite low, which in turn allows squirrels to survive falls from any height.