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Safety

Safety. Crash test videos. http://www.youtube.com/watch?v=sh1-ti8cCiw Introduction http ://www.youtube.com/watch?v=FnH_gvhI9OI Basic crash http://www.youtube.com/watch?v=d7iYZPp2zYY Seat belt and airbag http://www.youtube.com/watch?v=fPF4fBGNK0U Old vs new cars. Safety Features:.

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Safety

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  1. Safety

  2. Crash test videos • http://www.youtube.com/watch?v=sh1-ti8cCiw • Introduction • http://www.youtube.com/watch?v=FnH_gvhI9OI • Basic crash • http://www.youtube.com/watch?v=d7iYZPp2zYY • Seat belt and airbag • http://www.youtube.com/watch?v=fPF4fBGNK0U • Old vsnew cars

  3. Safety Features: • What features of a car are designed to protect a person in the event of a crash?

  4. Safety Features: • What features of a car are designed to protect a person in the event of a crash? • Answers might include: seatbelts, airbags, crumple zones, roll bars, safety glass, etc.

  5. Airbags and crumple zones • How do they protect the person in the car?

  6. Airbags • We modeled a human head with an egg. • Then, we dropped the egg until it broke.

  7. Airbags • The egg broke after a very short (5-7 cm) fall onto a rigid surface. • It made no noticeable crater and the impact took an un-measurably short amount of time.

  8. Why did they break?

  9. Why did they break? • The surface stopped the egg. • Momentum went to zero. • Kinetic energy went to zero.

  10. Why did they break? • The surface stopped the egg. • Momentum is reduced by an impulse. • Kinetic energy is reduced by work.

  11. Why did they break? • The surface stopped the egg. • Change in Momentum = F x t • Change in Kinetic energy = F x d

  12. Why did they break? • The surface stopped the egg. • Change in Momentum = F x t • Change in Kinetic energy = F x d • In each case, the force was greater than the strength of the eggshell

  13. Into sand. • The egg landed safely from a much higher drop (up to 1.6 m =160 cm) • Why?

  14. Into sand. • The egg landed safely from a much higher drop (up to 1.6 m =160 cm) • Why? • It took a longer distance and it took a longer time to come to rest.

  15. Into sand. • The egg landed safely from a much higher drop (up to 1.6 m =160 cm) Change in Momentum = F x t Change in Kinetic energy = F x d • As time increases, force decreases! • As distance increases, force decreases!

  16. After a 2.8 m fall into flour!How did it survive?

  17. Seatbelts • A seatbelt has to be strong enough to slow down a body exactly as fast as the seat decelerates. (If it tears, you go flying)

  18. Pressure=Force/Area • A thin belt will exert the same force as a thick belt, but it will cut into the body if it is too thin. • With a larger area, the pressure is reduced. • P=F/A

  19. How these objects show pressure issues in their design? • Kites • Boxing gloves • Snowshoes • Stiletto heels • Ice skates

  20. Units! • P=F/A • Force in Newtons • Area in m2 1N/m2= 1 Pascal (1 Pa) (a very small unit of pressure!)

  21. Magdeburg spheres: a demonstration of air pressure (1657) Put them together and pump out the air. A=.1 m2, air pressure=100,000 Pa resisted a team of oxen trying to pull them apart. • (requires about 10,000 N, the weight of 15 men)

  22. Circular motion On a roller coaster, you have to be going fast enough to get through the circle.

  23. Circular motion On a roller coaster, you have to be going fast enough to get through the circle. How fast is fast enough?

  24. Collect data to show the minimum height required to allow the weight to complete its circle without losing all tension on the string. Investigate (Release from here) • Height Radius Measure the height and radius while the weight is upside down at the top of the circle

  25. Data

  26. Calculations (Please show all of your work) • How do you calculate the velocity of the weight as the string hits the lowest bar? • What is the centripetal acceleration of the weight as it circles the bar? • Collect your results for all trials

  27. Only one set of data!

  28. Which average is better?

  29. Another set of data

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