Is this really possible?

Breaking down the physics of the krazy glue bungee

jump using a stopwatch and some assumptions

Approach:

•Observe the “test jump” in the Krazy Glue video • time the acceleration (free fall)• deceleration (slowing down) portions of the test jump.

•Using the times for the free fall and slowing down portions of the jump, and some assumptions about the weight of the jumper, calculate the force and stress on the bonded coupling.

Assumptions:

•Jumper weighs 150 lb•Neglect wind resistance•Diameter of the bonded coupling = 2 inches •The bungee cord behaves like a perfect spring, and has a constant spring constant throughout its range of motion.•The bonded coupling is only under load during the deceleration portion of the jump

Bungee Jump Schematic

Tf = Free Fall Time

Ts = Slow Down Time

The Ground

Bonded coupling

Bungee cord

Jumper

Bridge

Times

Free Fall Time Tf = 1.19357sec

Slow Down Time Ts = 1.23308sec

The Ground

Bonded coupling

Bungee cord

Jumper

Bridge

calculating the force on the bonding coupling the force on the bonded coupling in the Krazy Glue bungee jump

Formula Used:Newton’s second law of motion: F = ma + mg

F = Force (this is the force on the bonded coupling that we’ll calculate)m = mass (this is the mass of the jumper – 68kg)a = acceleration (this is the rate of slowing down due to the bungee cord or

“deceleration”)g = acceleration due to gravity (9.8m/sec2)

Calculate the acceleration: (Initial velocity – final velocity) / slowing down timeVi = Tf x g = 1.193571sec * 9.8m/s2 = 11.697 m/sVf = 0Slow down time (Ts)= 1.233077seca = 11.697m/s / (1.233077s) = 9.486026m/sec2

F = (m x a) + (m x g)F = (68kg * 9.486026m/sec2) + (68kg * 9.8m/sec2)F = 645.0498N + 666.4NF = 1311.4498NF = 294.8203614 lbs

Stress = F / AStress = 294.8203614 lbs / 3.14159in2Stress = 93.844315 psi

Surface Prep and Bonding•We prepped the surface of aluminum cylinders using a grit blaster as well as an acetone based solution. and bonded them together to form test coupons using and Krazy Glue.•We bonded together 7 different test coupons. They were bonded together using three different types of glue. We also tested how two of the different glues would behave when the surface was contaminated prior to bonding.

•#1: Aircraft Grade structural bonded joint•Surface prep: grit blaster, phosphoric acid anodizing, and bond primer •Glue: 3M Scotchweld EC2216

•#2: Krazy Glue•#3: Krazy Glue•#4: Contaminated Krazy Glue

•Contaminate: Cat Oil•#5: Boeing’s Krazy Glue•#6: Boeing’s Krazy Glue•#7: Contaminated Boeing’s Krazy Glue

•Contaminate: Cat Oil

Testing

Boeing Glue W/ Oil Boeing Glue Krazy Glue 3m Scotchweld EC 22160

200

400

600

800

1000

1200

1400

1600

Results (psi)

Boeing GlueKrazy Glue W/ Oil Krazy Glue

93.844315 psi

Boeing Glue w/oil Boeing Glue Boeing Glue Krazy Glue w/oil Krazy Glue Krazy Glue 3M Scotchweld EC2216

Str

ess

(psi

)

Glue