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Question 2: Why can squirrel jump from a tree branch to the ground and run away undamaged while a human could break a bone in such a fall?


When a body is falling in air, there are two force acting on it.

  • Its weight, acting downwards and is proportional to its mass.
  • Drag force, acting upward and is proportional to exposed area of the body. Exposed area means the spread of the body.

So, the net force basically depends on the mass and exposed area. If the body is lighter and its exposed area is comparatively less, the drag force will be large and the body will fall slow. On the other hand if the body is heavier and its exposed area is comparatively less it will fall speedily.

Now a squirrel has very little mass and the spread of its body is comparatively large. Therefore, when it jumps down the tree, the drag force is larger. The squirrel comes down with a much lower velocity and remains undamaged. On the other hand, a man’s weight is much larger as compared to its spread or exposed area. Therefore, the drag force is also greater and he hits the ground with a greater velocity and gets his bones broken.

Follow up question

Consider the following diagram. An object is set to fall in two different orientations. Which one will have less terminal velocity? Which one will reach the ground soon?

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