Terminal velocity is another one of those phrases you encounter in skydiving. But what exactly is meant by the term and what is the average terminal velocity for a human in freefall?

What is Terminal Velocity?

Terminal velocity can be thought of as the point at which your body ceases to accelerate during freefall. Why does it stop accelerating? I’ll offer the zen definition: “your body & the air find balance (dude,)” Not good enough for you? Fine. Here comes the science: “ Air resistance exists because air molecules collide …. Creating an upward force opposite gravity. This upward force will eventually balance the falling body’s weight. It will continue to fall at a constant velocity.” (thanks to the physics factbook.) This “constant velocity” then is what we call “terminal velocity.”

Factors that Influence Terminal Velocity

Terminal velocity is not a static number for a body in freefall. There are many things that can influence the speed reached – including weight, and body position. Air density also matters – but since we’re not jumping from 80,000 ft, let’s focus on the first two.

Weight is important because (as we learned above,) air resistance must balance weight . So, as common sense (and skydiving experience) would dictate – a heavier individual will fall “faster” and reach a higher terminal velocity than will a lighter skydiver in a similar body position.

Body position is important because of resistance as well. In very fast freefall positions such as a head-down skydive – the surface area of the body on which “molecules can collide” is very limited. Less resistance equals greater speed. The opposite is true as well – the more surface area an individual provides to the relative wind (as in a belly-to-earth body position) the slower the body will fall.

Terminal Velocity: Average Speeds in Freefall

What sorts of speeds are we talking, anyway? Well – no one can quite decide what the “averages” are for different types of body positions in the skydiving community (seriously, SO many different ideas!) So, we will once again turn to science ( I promise not to blind you.) This is a little tricky because scientists tend to want to talk about things in units like “meters.” Ugh. Converting as closely as possible to mph – the numbers shake out to something like the following:

For a slow falling body (offering much resistance, as in a belly-to-earth dive) : 120 mph (53 m/s)

For a fast moving body (offering as little resistance as possible, as in a head-down dive) : up to 200 mph

Additional Notes: Terminal velocity is not reached until after the body has been falling for sometime after exit. Also, while deploying your canopy while going terminal on a belly dive is fine (110 mph being suggested by some as the optimum speed for canopy deployment,) you would not wish to deploy while going terminal at 200 mph. This is why (in addition to attaining the correct pre-deployment body position of course,) skydivers transition to a belly-to-earth position and “slow down” prior to deploying their main.

Additional Resources: If you are really into math and love thinking about things like "drag coefficients" than you may be able to calculate your own personal terminal velocity with Nasa's Terminal Velocity Calculator. If you still have some time left on your Saturday night; you can always change the settings to learn how fast you would fall in the atmosphere of Mars.