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The Paper And The Weight

The Paper And The Weight. Air resistance. T.H. Which will fall faster, the 1 kg weight or the sheet of paper?. Why is the 1 kg weight falling faster?. Aristotle taught that the speed of a falling body was proportional to its weight.

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The Paper And The Weight

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  1. The PaperAnd The Weight Air resistance T.H. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan

  2. Which will fall faster, the 1 kg weight or the sheet of paper? PDST Resources for Leaving Certificate Physics2

  3. Why is the 1 kg weight falling faster? PDST Resources for Leaving Certificate Physics3

  4. Aristotle taught that the speed of a falling body was proportional to its weight. PDST Resources for Leaving Certificate Physics4

  5. This view lasted for almost 2000 years until Galileo contradicted Aristotle. PDST Resources for Leaving Certificate Physics5

  6. Who was right? • If Galileo was right, why does the 1 kg weight fall faster than the sheet of paper? PDST Resources for Leaving Certificate Physics6

  7. Air Resistance • A falling body is acted on by a number of forces. • Its weight, due to the force of gravity, Fg, acts downwards. • Air resistance, or drag, Fd, acts upwards. PDST Resources for Leaving Certificate Physics7

  8. Terminal Velocity • As an object falls, its velocity increases. • This causes its air resistance, Fd, to increase. • When the air resistance, Fd, equals the weight, Fg, the object moves at a constant velocity, called its terminal velocity. PDST Resources for Leaving Certificate Physics8

  9. Skydiving • With arms out, a skydiver reaches a terminal velocity of about 55 m s–1. • With arms and legs folded up, skydivers have reached terminal velocities of about 90 m s–1. • Skydiving head down at high altitude, Joseph Kittinger has reached a terminal velocity of 274 m s–1. PDST Resources for Leaving Certificate Physics9

  10. Question • Convert Joseph Kittinger’s terminal velocity of 274 m s–1 to km hr–1. PDST Resources for Leaving Certificate Physics10

  11. Answer Note: You might find it useful to learn to convert m s–1 to km hr–1 by multiplying by 3.6 PDST Resources for Leaving Certificate Physics11

  12. Back to the 1 kg weight and the sheet of paper • Can we reduce the air resistance acting on the sheet of paper so that it falls as fast as the 1 kg weight? • How? PDST Resources for Leaving Certificate Physics12

  13. Roll it into a ball to reduce its surface area! PDST Resources for Leaving Certificate Physics13

  14. Now That Air Resistance Is Less Of A Factor, They Fall At the Same Rate. PDST Resources for Leaving Certificate Physics14

  15. Another Demonstration • Here is a coin and a piece of paper. • Which will fall faster? • Why? PDST Resources for Leaving Certificate Physics15

  16. Why Is The Paper Falling More Slowly Than The Coin? PDST Resources for Leaving Certificate Physics16

  17. Again, It’s Air Resistance • Place the paper on the coin. • Drop the coin. • The paper stays on the coin, i.e. they fall at the same rate when air resistance is not such a factor. PDST Resources for Leaving Certificate Physics17

  18. References • Air Resistance • Terminal Velocity • Joseph Kittinger • Galileo • Aristotle PDST Resources for Leaving Certificate Physics18

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