1. The Paper And The Weight
Air resistance
T.H.
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2. Which will fall faster, the 1 kg weight or the sheet of paper?
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3. Why is the 1 kg weight falling faster?
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4. Aristotle taught that the speed of a falling body was proportional to its weight.
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5. This view lasted for almost 2000 years until Galileo contradicted Aristotle.
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6. Who was right?
If Galileo was right, why does the 1 kg weight fall faster than the sheet of paper?
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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.
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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.
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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.
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10. Convert Joseph Kittinger’s terminal velocity of 274 m s–1 to km hr–1.
Question
Convert Joseph Kittinger’s terminal velocity of 274 m s–1 to km hr–1.
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11. Answer
Note: You might find it useful to learn to convert m s–1 to km hr–1 by multiplying by 3.6
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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?
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13. Roll it into a ball to reduce its surface area!
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14. Now That Air Resistance Is Less Of A Factor, They Fall At the Same Rate.
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15. Another Demonstration
Here is a coin and a piece of paper.
Which will fall faster?
Why?
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16. Why Is The Paper Falling More Slowly Than The Coin?
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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.
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18. References Air Resistance Terminal Velocity Joseph Kittinger Galileo
Aristotle
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