Monday, November 21, 2011

Physics of Skydiving

Skydiving is a great example of many of the physics concepts that we have discussed thus far in our class. First we can examine the forces acting on a skydiver as he is falls. Initially as the diver jumps out of the plane the main force acting on him is a gravitational force. There is also a really small buoyant force which can largely be neglected since it is based on the density of the 'fluid,' in this case air, surrounding the skydiver. As the skydiver accelerates downwards due to gravity his velocity increases, which subsequently increases the drag force acting on him due to air resistance which is dependent on the skydiver's velocity. He will eventually reach his terminal velocity, the speed at which he is no longer accelerating because the force due to gravity is exactly balanced by the drag force. However this terminal velocity is still really large and it would be a bad idea for a skydiver to hit the ground going at this speed, so the use of a parachute comes into play. A parachute increases the skydiver's area, another variable of the drag force. So as soon as the skydiver deploys his chute he is still going pretty fast but now greatly increased his area and thus his drag force. This causes a rapid net force upwards, the force of drag is much greater than the force of gravity, which causes him to rapidly decelerate and slow down. As his velocity slows his drag force also decreases and eventually he once again comes to a new terminal velocity where the forces are balanced, however this second terminal velocity is much lower than the first so he won't injure himself upon impact with the ground.

This is a fun animation which shows all the forces acting on a skydiver, check it out in motion at this site!

Here is a link to an extreme skydiver

If you wanted to calculate this terminal velocity all you would need to do is set the drag force equal to the force of gravity and solve for v.

Fun facts:

Because air density increases with decreasing altitude, this causes an increased buoyant force near the surface of the earth. The buoyant force causes the terminal velocity to decrease by 1% every 525ft.

The world record for skydiving speed of 614 mph was obtained at high altitude where the less dense air reduces drag and buoyant effects.

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