A bungee jump is a short physics lesson you feel with your whole body. For a second or two you fall freely. Then the cord tightens, stretches and pushes back, so for a moment you feel several times heavier than normal, before a series of smaller bounces fades out. This guide explains each stage, what the numbers look like, why the cord is matched to your weight, and how a head-first dive differs from stepping off feet first.
The three stages of a bungee jump
Physics teachers usually split a jump into three stages: a free fall while the cord is still slack, a stretch stage until the cord reaches its longest point, and a rebound stage of gradually shrinking bounces [1].
| Stage | What happens | What you feel |
|---|---|---|
| Free fall | The cord is slack and gravity does all the work. You speed up by about 9.8 m/s every second [2]. | Weightlessness, close to 0 g, plus rushing air and a lurch in your stomach [3] |
| Stretch | The cord tightens and pulls back harder the further it stretches, until you stop at the lowest point [4]. | A smooth but firm squeeze through the harness. This is the heaviest moment of the jump. |
| Rebound | The cord springs you back up, and each bounce is smaller than the last. | Alternating light and heavy moments, then hanging still |
Free fall: why it feels like nothing is holding you
Standing on the ground, you feel 1 g because the ground is pushing up on you. In free fall nothing pushes back, so you feel weightless, close to 0 g [3]. That is the “stomach drop” people describe, and it is why the first second of a jump feels so much stranger than the rest.
The numbers rise quickly. Ignoring air resistance, a 15 m free fall takes about 1.7 seconds and ends at about 62 km/h (39 mph). Speed grows with the square root of the distance fallen, so falling four times as far only doubles your speed [2]. Air resistance cuts the real figures a little.
There is one surprise for physicists. A bungee cord has weight, and as it unfolds it pulls on your feet. A 2010 study by researchers and secondary school students in the Netherlands showed that, with the cord’s mass included, a jumper can briefly accelerate faster than gravity during the free fall [1].
The stretch: where the g-forces come from
Once the cord is taut it behaves roughly like a spring. The further it stretches, the harder it pulls back. Textbooks describe this with Hooke’s law, F = kx, where k is the cord’s stiffness and x how far it has stretched [5]. Real bungee cords are more complicated. The common braided type is made of many latex strands inside a tough cover, sometimes pre-stressed, so it already resists stretching at its natural length [4]. The simple model still explains what you feel.
At first the cord pulls less than your weight, so you keep speeding up. At some point the pull equals your weight and you briefly stop accelerating, which is the point of maximum speed. After that the cord pulls harder than your weight, you slow down, stop at the bottom and spring back up [4].
Energy explains why the bottom is the heaviest moment. All the energy you gain from falling is stored in the stretched cord, as elastic potential energy of ½kx² [6]. A simple worked example helps:
- A jumper falls 50 m in total on a cord 15 m long, so the cord stretches by 35 m.
- In the simple model, the cord’s pull at the bottom equals twice the jumper’s weight multiplied by 50 ÷ 35, which works out to about 2.9 times their body weight.
- So for a fraction of a second, the jumper feels close to 3 g.
That is an idealised figure. Air drag and the cord’s own energy losses lower it, and real cords don’t follow Hooke’s law exactly. A University of Leicester student paper estimated about 1.7 g for the 233 m Macau Tower jump [7]. For comparison, AJ Hackett says its Nevis Catapult, which launches people horizontally, reaches up to 3 G [8].
Why the cord stretch is regulated
The stretch ratio is so important to how a jump feels that some regulators specify it. Illinois requires a cord to stretch to at least 2.5 times its unloaded length across its designed weight range, and to no more than 4 times its unloaded length at its maximum designed load. The unloaded length of the whole rigging system must also be less than half the designed extended length [9].
That rule has a practical meaning. Because the cord grows to at least two and a half times its length, the stopping distance is long and the deceleration is spread out, rather than coming as a sudden jolt. The upper limit keeps the stretch predictable, so the operator can be sure the jumper stops well clear of the ground or water.
It is also why you are weighed before you jump. A heavier jumper stretches the same cord further, so cords are matched to a weight range and the crew selects one for you [10][9]. Under the Illinois rules, choosing the cord is one of the jump master’s responsibilities [9]. If your weight is wrong on the form, the cord may not be right for you, so let the crew weigh you rather than giving them a number.
The bounce, and why it dies away
At the bottom the cord springs you back up, often a surprisingly long way. Each bounce is smaller than the last because some energy is lost each time, mainly as heat inside the stretching cord and to air resistance. After a few rebounds you hang and swing gently until you are lowered or pulled back up. AJ Hackett’s Nevis jump, from 134 m, is billed as 8.5 seconds [11]. A pure free fall from that height would take only about 5.2 seconds, so much of the jump is spent with the cord already working.
Many people find the bounces the most enjoyable part. The fear peaks at the edge, and by the second bounce you know the cord has held. Letting your body stay loose, rather than tensing up, makes the rebounds feel smoother. A swing works differently: it uses a rope rather than an elastic cord, so after the free fall you swing in an arc instead of bouncing [10].
Head first or feet first?
The classic bungee jump is a head-first dive with the cord attached at your ankles. Illinois describes an ankle binding as a harness that wraps the ankles together and attaches you to the cord [9]. After accidents in which jumpers became detached, many operators started using a body harness as well, at least as a backup for the ankle attachment [4]. Some jumps are designed to be done feet first or running. AJ Hackett’s Ledge Bungy in Queenstown, for example, uses a waist harness and a run-and-jump start [12].
The physics of the fall is the same either way: you fall at the same rate and the cord stores the same energy. What changes is how you feel it:
- Head first: you see the ground rushing towards you, and at the bottom the load goes through your ankles and legs. You end up hanging upside down.
- Feet first or seated in a body harness: the load goes through your waist and thighs, and you finish the right way up, or close to it.
Hanging upside down has a measurable effect. In a 2008 study of 120 jumpers at Bloukrans Bridge in South Africa, 84.2% had small spots of bleeding on the white of the eye afterwards. The researchers linked this to blood pooling in the head while jumpers hung upside down for 2 to 3 minutes before being brought up. Vision was unchanged in 83.3% of cases, but one jumper developed a detachment of the gel inside both eyes [13]. Eye damage is the complication reported most often after bungee jumps, and it is thought to come from the sudden rise in pressure in the upper body as the cord recoils [4]. If you have an eye condition, mention it at check-in.
What the physics can’t tell you
The equations describe an idealised jump. Whether a real jump is safe depends on things physics lessons leave out: the right cord for your weight, correctly fitted harnesses, connections that are checked every time and cords retired when they are worn. Illinois, for example, requires the jump master to inspect the cord at least four times a day and to retire it after a set number of jumps or set period of time [9]. For what to look for in an operator, see how to choose a reputable bungee operator.
FAQ
How many g-forces do you feel on a bungee jump?
Close to 0 g during the free fall, then a peak at the bottom when the cord is fully stretched. A simple model gives up to about 3 g for a typical jump, and a student estimate for the Macau Tower jump was about 1.7 g [3][7].
How fast do you fall on a bungee jump?
Ignoring air resistance, about 62 km/h (39 mph) after a 15 m free fall, and faster on longer cords. You reach top speed shortly after the cord starts to stretch [2][4].
How far does a bungee cord stretch?
A lot. Illinois requires cords to stretch to at least 2.5 times their unloaded length across their weight range, and no more than 4 times at maximum load [9].
Why do they weigh you before a bungee jump?
A heavier jumper stretches the same cord further, so cords are matched to weight ranges. The crew picks the right cord for your weight [10][9].
Is a head-first bungee jump more dangerous?
The fall itself is the same. Head-first jumps finish with you hanging upside down, and a Bloukrans study found most jumpers had small, usually harmless spots of bleeding in the eyes afterwards [13].
Why do you bounce on a bungee jump?
The stretched cord stores the energy of your fall and springs you back up. Some energy is lost with each bounce, so the bounces get smaller until you hang still [6][4].
Sources
- Heck, Uylings and Kędzierska (2010). Understanding the physics of bungee jumping. Physics Education 45(1):63–72
- OpenStax College Physics 2e: Gravitational potential energy
- Wikipedia: g-force (what 1 g and 0 g mean)
- Wikipedia: Bungee jumping (how the cord slows the jumper, braided cords, ankle and body harnesses, eye injuries)
- OpenStax College Physics 2e: Hooke’s law, stress and strain revisited
- OpenStax University Physics Volume 1: Potential energy and conservation of energy (elastic potential energy)
- Kerr et al. (2011). Macau Tower g forces. Physics Special Topics 10(1), University of Leicester
- AJ Hackett: Nevis Catapult (150 m, up to 3 G)
- Illinois Administrative Code tit. 56, § 6000.340: Bungee jumping (cord stretch limits, ankle bindings, dynamic loading)
- AJ Hackett Bungy New Zealand: FAQs (bungy vs swing, weigh-in)
- AJ Hackett: Nevis Bungy (134 m, 8.5 seconds)
- AJ Hackett: Ledge Bungy (47 m, waist harness, run and jump)
- Prospective study of ocular findings in 120 jumpers at Bloukrans Bridge (German Medical Science, 2008)
Image credits
- Photo: Dariusz Jemielniak ("pundit") / Wikimedia Commons (CC BY-SA 4.0)
- Photo: Poni Abraham / Wikimedia Commons (CC0)
- Photo: Lilly M / Wikimedia Commons (CC BY-SA 3.0)