EGR 105 Foundations of Engineering I

Fall 2007 – Week 4

EGR105 – Week 4 TopicsProject Work – Bungee Cord Characterization Work in Teams

- Follow Procedures Outlined in Handout 2- Mark Cord- Use Test Stand- Add Weights and Measure Resulting Extension - Record Data- Enter Data into Excel Spreadsheet and Do Calculations & Plots

From Last LectureAt the Bottom, distance d0

• Velocity v is now zero, so

• We could solve for d0 if we knew F. So we need to characterize bungee cord!(this week)

Ld

Ld

dssFmgd

dssFdhgmmgh

0

0

0

0

0

0

)(

)(

v = 0

d0

L

Typical Models for Cords• Linear Model (Hooke’s Law): • More Realistic Nonlinear Model

Cubic Model:

kssF )(

33

221)( sksksksF

Stretch s

Force F(s)Linear

CubicBut You First Want to Gather Experimental Data on Your Team’s Cord

Bungee Cord TestingCharacterization of F(s)

lo

Wooden Peg

Cord

Loop Knot

?W

- Mark Cord- Use Test Stand- Add Weights- Measure Resulting Extension - Record Data

Typical Data Expected

Force F(s)

ol

s

LengthOriginal

Stretch

Most Likely Will Be Nonlinear

Typical Data in Excel

  lo = 4  

Weight(lb) l (l-lo) (l-lo)/lo

0 4 0 0

1 4.4 0.4 0.1

1.44 4.6 0.6 0.15

2 5.2 1.2 0.3

2.44 5.7 1.7 0.425

3 6.3 2.3 0.575

3.44 6.9 2.9 0.725

4 7.6 3.6 0.9

5 8.1 4.1 1.025

6 8.6 4.6 1.15

Assignment # 4

• Enter Data Into Excel Spreadsheet • Calculate Δs and Δs/lo• Make Plot of F versus Δs/lo• Keep Plot on Same Page as Data• Save as teamnumber_4.xls• Turn in hard copy • Due October 4