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Freshly Baked Science

The Physics of Bungee Jumping

8th December 2018

Jumping off the edge of a bridge and experiencing free-falling for a few seconds, before being caught by your cord is not for everyone. Bungee jumping is definitely an acquired experience and is best reserved for serious thrill-seekers! But there’s nothing stopping you finding a little bit more about how bungee jumping works… you never know, it may make you feel better about it and end up booking one by the end of this article… maybe.

The basic process of bungee jumping is fairly obvious. The jumper, attached to a cord, jumps off something. They then free fall, until the cord becomes tight, at which point they spring back slightly and bounce around before coming to a swaying ‘standstill’.

To understand the physics of a bungee jump, the full jump can be split into 3 parts.
 

  1. The free-fall of the jumper (while the bungee cord is still relaxed)
     

  2. The bungee cord being stretched
     

  3. The bungee cord recoiling

The free-fall

When the jumper is experiencing free-fall, the only force acting on them is gravity. As there is only one single, constant force acting on the jumper at this point, there is a constant acceleration towards the ground below. At this point, the jumper will be accelerating at a rate of 9.8m/s2 (the acceleration of gravity).

Cord stretches

Once the jumper gets to a distance away from the point of attachment that is equal to the length of the bungee cord, the cord will begin to stretch. At this point, gravity won’t be the only force acting on the jumper. The stretch of the cord creates tension, which is an upwards force (opposite to gravity). The tension force increases as the cord stretches and will eventually become greater than the force of gravity, causing a switch in direction. The acceleration is now upwards.

Cord recoils

When the cord reaches its full stretching potential, it retracts, which causes the bungee jumper to fling upwards. While the cord is recoiling, the tension is decreasing, meaning that the upwards acceleration is not constant. Once the tension decreases sufficiently enough that the force of gravity is greater once again, the jumper will repeat the full process, beginning with the free-fall.

So why doesn’t the jumper just keep bouncing around forever?

There is a third force acting on the jumper; air resistance. Air resistance causes the height of the bungee jumpers bounce to decrease with every cycle. Without air resistance, the jumper would just continue bouncing around forever (we think the adrenaline may wear off after a few minutes).

 

We’d love to know the most adventurous thing you’ve ever done! Let us know on social media (@wonkscience) with the hashtag #STEMintoChristmas!

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