MadSci Network: Zoology

Re: If you dropped a dog tick from an airplane or tall building, would it die?

Date: Tue Feb 22 06:24:00 2005
Posted By: Andy Goddard, Staff, Teaching and Learning Resources, Strathclyde University
Area of science: Zoology
ID: 1107621068.Zo

Hi Jordan!

I suspect it would survive.

Think of a ship moving through water. The bow-wave of the ship is caused by
the ship moving water out of the way to allow its passage. The force
required to make the bow-wave is balanced by a force made on the ship,
acting as a deceleration (braking) force which acts against the ship's motion.

This force is dependent on the density and viscosity of the water, the
shape and surface area of the ship, and the velocity of the motion squared.

This last term is a particularly interesting one. Let's imagine dropping
bodies in air. Air is thinner than water - so the drag will be less (this
is one reason why aircraft fly faster than passenger liners can sail).
Gravity acts on the body, accelerating it so that the velocity rises. A
body falling in air, assuming the air doesn't change much in density, and
that the body doesn't change shape, will speed up over time. As the speed
increases, the drag will rise quickly. At some point the drag force (trying
to slow down the body) will equal the force of gravity (trying to speed up
the body) and the body will achieve a stable velocity: this is known as the
"terminal velocity".

For a person in normal clothing the terminal velocity is around 200km/hr.
But remember I mentioned the shape and surface area of the moving body were
important? The same person with a deployed parachute might land at a mere
10km/hr. In this instance the terminal velocity is less, precisely because
the surface area is greater, for the same falling mass.

If I divided the size of this person by four, the surface area would be
1/16th, and the mass would be 1/64th. The terminal velocity would therefore
be about 1/4 of the 200km/hr for the full-sized version. There are many
tales of cats (which are about the size of my 1/4-sized person) surviving
falls over many stories that would kill people. 

The tick (of about the same density as a human) is about 1/100th our
length. I suspect a falling tick (or any other insect, for that matter)
would reach its terminal velocity of about 2km/hr in very little time, and
easily survive a landing from any given height.

I hope this helps answer your question!


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