I am sure you all remember 1960 (!) when Joe Kittinger jumped from an altitude of 31,333 metres setting an unbroken record for the highest parachute jump. Just to put that in persective, a jumbo jet flies at about 12,000 metres. Now, a base jumper called Felix Baumgartner is planning to jump from 36,575 metres. He is expecting to reach supersonic speeds (340.29 m/s or 760.21 mph) within about 35 seconds of his fall.
There are a number of interesting issues with this adventure…
Terminal Velocity
When an object falls through the air it accelerates as a result of gravity pulling it towards Earth. As it travels faster the force of air resistance pushing against it increases. In fact for every doubling of the object’s speed the air resistance quadruples. Quickly the air resistance is equal to the force of gravity and the object stops accelerating and travels at a constant speed. This is called terminal velocity. For sky divers jumping from planes without breathing apparatus this is about 125 mph (56 m/s) when spreading their body out to maximise air resistance and 200 mph (89 m/s) when in a dive with a smaller cross-sectional area. The reason that Felix is going to travel somewhat quicker is that the air is so thin at the altitude he will leap from that the air resistance is very much lower.
Armstrong Line
At an altitude of around 19,000 metres we reach the Armstrong line which is where the atmospheric pressure is so low that water boils at 37°C. This is roughly body temperature so if you were to be exposed to this altitude all the fluids in your body would boil and you would become a seething mass of exploding eyeballs and boiling blood. Nice.
Felix is going to have to wear a space suit for his jump and hope that the helmet does not crack when he breaks the sound barrier and experiences the shockwave known as a sonic boom.
Sonic Boom
As Felix travels through the air he will make it move away from him in waves similar to those you see from the bow and stern of boat. These waves will travel at the speed of sound so when he reaches the speed of sound they will not be able to get away from one another causing a shock wave known as a sonic boom. This could cause him to black out or enter an uncontrolled spin. His suit is going to be fitted with sensors to monitor his heart rate in case he passes out under the stresses caused by his acceleration.
[The two F18 planes above are passing through the sound barrier just as they pass the cameras filming them. You can see the clouds of steam formed as the ‘sonic boom’ occurs.]
He will eventually need to slow down to about 110 mph (49 m/s) so that he can open his parachute, increasing his cross-sectional area and hence the air resistance, so that he will be able to slow down enough to land. For more about people jumping off things and hoping to survive you might like my previous post here.
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