Steel balls

1. Steel balls Topic 3 Taiwan Representative

2. Outline • Question • Experimental set up: Vertical collision • Materials: Paper, Plastic, and Metal sheets • Experimental results: Hole size v.s materials, height… • What we learned & discussion • Conclusion

3. Question • Colliding two large steel balls with a thin sheet of material (e.g. paper) in between may "burn" a hole in the sheet. Investigate this effect for various materials.

4. Experimental Setup: vertical collision H Sheet 1 m

5. Materials • 1. Paper (Burning point: 130o~232oC) 2 mm 5 mm Reference:http://wiki.answers.com/Q/What_is_the_Burning_point_of_paper

6. Burned Burned O2 O2 Greatly heated Greatly heated A thin piece of material left on the ball Inflammable materials Paper

7. Materials • 2. Plastic (Melting Point: 106~114℃) (Soften temperature: 80~98℃) 3 mm 4 mm

8. Cooled down Wrinkles Compressed Into thin layer Melted Non-flammable materials Plastic

9. Materials • 3. Aluminum foil (Melting point: 660 C) 6 mm 5 mm

10. Non-flammable materials Aluminum foil Melted Concentric circles wrinkles Compressed

11. Materials • 4.Copper foil (Melting Point: 1083.0 °C) 2mm 5 mm Reference:www.chemicalelements.com/elements/cu.html

12. Non-flammable materials Copper foil Melted ?? Depends on condition Concentric circles wrinkles Compressed

13. Plastic Paper = 7.6 cm H = 7.6 cm = 7.6 cm = 7.6 cm

14. Height v.s. Materials

15. Height v.s. Materials

16. Height v.s. Materials

17. Height v.s. Materials

18. Estimation of physical parameters during collision The highest temperature Tmax.= ? Duration ∆t = ? Collision area A=? Average pressure P = ? Conducted heat ∆Q = ? Adiabatic process? i.e. ∆W >> ∆Q

19. Tmax.=?  We can melt Al foil . Melting point of Al = 660 ℃. Cooled after melted

20. Duration ∆t = ? Our high speed video: 230 μs/frame

21. t=0 Dropping ball Edge of pillar Material Fixed ball

22. t=230μs Dropping ball Edge of pillar Material Fixed ball

23. t=230μs x 2 Dropping ball Edge of pillar Material Fixed ball

24. t=230μs x 3 Dropping ball Edge of pillar Material Fixed ball

25. Duration ∆t = ? 1. Our high speed video: 230 μs/frame ∆t < 230 μs our mball=287 g 2. From reference We can conclude : ∆t < 230 μs R. Hessel, A. C. Perinotto, R. A. M. Alfaro, and A. A. Freschia, Am. J. Phys. 74 3, 176 (2006).

26. Diameter: 1.58± 0.08 mm Estimate A from the melted Al foil . Collision area A=? Diameter ~ 1.6 mm Al foil

27. Average pressure P = ? m=287 g, H=50 cm, g=9.8 m/s2, A< π(0.8mm) 2 , ∆t < 230 μs

28. Work ∆W=? σ Conducted heat ∆Q=? ∆T < 1000 ℃ A=πr2 ~ 2 x 10-6 m2 Pressure P > 1.2 x 109 Nt/m2 Collision Area A=πr2 ~ 2x10-6 m2 Thickness of sheet ∆d= 10-4 m

29. Heat produced Using the lowest production of work, Increase ofΔT , => Higher than melting point of Al: 660

30. Adiabatic process?? • Work done during collision ∆W > 3.9 ×10-1 (J) • Heat conducted during collision : • ∆Q < 2.9 ×10-4 (J) • ∆W >> ∆Q •  Adiabatic process Tlow Thigh

31. Conclusion • Height: Diameter of holes increases as height increases • Collision Area: • Burning • Melting

32. P T P T Colliding process

33. Burning O2 O2

34. Melting

35. Conclusion Height: Diameter of holes increases as height increases Collision Area: Melting Burning Adiabatic Process is the main reason holes are burned because: Δt is small Area is small Pressure is high

36. Conclusion • Height: Diameter of holes increases as height increases • Collision Area: • Melting • Burning • Adiabatic Process is the main reason holes are burned because: • Δt is small • Area is small • Pressure is high