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# Stressing Silly Putty

Conduct stretch-tests on homemade silly putty to explore how engineers design more realistic crash test dummies.

#### Key Questions

• How do crash forces apply stress to human tissue?
• How can stress-testing materials improve crash test dummy performance?

#### Student Directions

1. View the Introduction video.
3. Do the activity and begin answering the analysis questions.
4. View the Conclusion video and finish answering the analysis questions.
5. View the video segment of "When Physics Meets Biology" to help review the science concept(s).

Creep: The response of a viscoelastic material such as Silly PuttyÂ® when a constant stress force is applied

Critical Stress Limit: the maximum amount of stress a material can withstand before failure (breaking)

Strain: a measure of how an object reacts to stress (e.g., how much its shape or size changes when stretched)

Strain Rate: how fast a material is stretched. Viscoelastic materials are strain ratedependent. For example, if you quickly stretch Silly PuttyÂ® (with a fast strain rate), then it breaks immediately; yet if you stretch it slowly (with a slow strain rate), it is more elastic and does not break

Stress: the average force exerted over a defined area

Viscoelastic: materials like Silly PuttyÂ® that exhibit the characteristics of both a solid and a liquid

Conduct stretch-tests on homemade silly putty to explore how engineers design more realistic crash test dummies.

#### Key Questions

• How do crash forces apply stress to human tissue?
• How can stress-testing materials improve crash test dummy performance?

#### Student Directions

1. View the Introduction video.
3. Do the activity and begin answering the analysis questions.
4. View the Conclusion video and finish answering the analysis questions.
5. View the video segment of "When Physics Meets Biology" to help review the science concept(s).
##### Vocabulary

Creep: The response of a viscoelastic material such as Silly PuttyÂ® when a constant stress force is applied

Critical Stress Limit: the maximum amount of stress a material can withstand before failure (breaking)

Strain: a measure of how an object reacts to stress (e.g., how much its shape or size changes when stretched)

Strain Rate: how fast a material is stretched. Viscoelastic materials are strain ratedependent. For example, if you quickly stretch Silly PuttyÂ® (with a fast strain rate), then it breaks immediately; yet if you stretch it slowly (with a slow strain rate), it is more elastic and does not break

Stress: the average force exerted over a defined area

Viscoelastic: materials like Silly PuttyÂ® that exhibit the characteristics of both a solid and a liquid