Stressing Over Pencil Pressure

Use pencil push-tests to learn the difference between force and pressure and explore how safety features protect human bodies in a crash.

Key Questions

• How can magicians lay on a bed of sharp nails unharmed?
• How are force, pressure, and stress relevant in engineering strong and safe vehicles?

Student Directions

1. View the Introduction video.
2. Download and print the Student Activity Sheet.
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).

Force: a push or pull that can cause a mass to accelerate, measured in Newtons (N)

Pressure: the amount of force applied over a given surface area; P = F/A.

Stress: the average internal force applied per unit of crosssectional area of a material; σ = stress = F/A

Stress test: applying pressure to stress a material until it fails