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Freefall

Freefall. Acceleration. Galileo increased the inclination of inclined planes. Steeper inclines gave greater accelerations. When the incline was vertical, acceleration was max, same as that of the falling object.

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Freefall

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  1. Freefall

  2. Acceleration Galileo increased the inclination of inclined planes. • Steeper inclines gave greater accelerations. • When the incline was vertical, acceleration was max, same as that of the falling object. • When air resistance was negligible, all objects fell with the same unchanging acceleration.

  3. Free Fall Falling under the influence of gravity only - with no air resistance • Freely falling objects on Earth accelerate at the rate of 10 m/s/s, i.e., 10 m/s2 (more precisely, 9.8 m/s2).

  4. Free Fall The greater the mass of the object… • the greater its force of attraction toward the Earth. • the smaller its tendency to move i.e., the greater its inertia. So, the acceleration is the same. It is equal to the acceleration due to gravity: 10 m/s2 (precisely 9.8 m/s2).

  5. Free Fall When acceleration is g—free fall • Newton’s second law provides an explanation for the equal accelerations of freely falling objects of various masses. • Acceleration is equal when air resistance is negligible. • Acceleration depends on force (weight) and inertia.

  6. Free Fall—How Fast? The velocity acquired by an object starting from rest is • So, under free fall, when acceleration is 10 m/s2, the speed is • 10 m/s after 1 s. • 20 m/s after 2 s. • 30 m/s after 3 s. • And so on.

  7. Free Fall—How Far? The distance covered by an accelerating object starting from rest is • So, under free fall, when acceleration is 10 m/s2, the distance is • 5 m after 1 s. • 20 m after 2 s. • 45 m after 3 s. • And so on.

  8. Free Fall CHECK YOUR NEIGHBOR At one instant, an object in free fall has a speed of 40 m/s. Its speed 1 second later is • also 40 m/s. • 45 m/s. • 50 m/s. • None of the above.

  9. Free Fall CHECK YOUR ANSWER At one instant, an object in free-fall has a speed of 40 m/s. Its speed 1 second later is • also 40 m/s. • 45 m/s. • 50 m/s. • None of the above. Comment: We assume the object is falling downward.

  10. Non-Free Fall Terminal speed • occurs when acceleration terminates (when air resistance equals weight and net force is zero). Terminal velocity • same as terminal speed, with direction implied or specified.

  11. Non-Free Fall—Example • A skydiver jumps from a plane. • Weight is the only force until air resistance acts. • As falling speed increases, air resistance on diver builds up, net force is reduced, and acceleration becomes less. • When air resistance equals the diver’s weight, net force is zero and acceleration terminates. • Diver reaches terminal velocity, then continues the fall at constant speed.

  12. Non-Free Fall CHECK YOUR NEIGHBOR As the skydiver falls faster and faster through the air, air resistance • increases. • decreases. • remains the same. • Not enough information.

  13. Non-Free Fall CHECK YOUR ANSWER As the skydiver falls faster and faster through the air, air resistance A. increases. • decreases. • remains the same. • Not enough information.

  14. Non-Free Fall CHECK YOUR NEIGHBOR As the skydiver continues to fall faster and faster through the air, net force A. increases. • decreases. • remains the same. • Not enough information.

  15. Non-Free Fall CHECK YOUR ANSWER As the skydiver continues to fall faster and faster through the air, net force A. increases. • decreases. • remains the same. • Not enough information.

  16. Non-Free Fall CHECK YOUR NEIGHBOR As the skydiver continues to fall faster and faster through the air, her acceleration • increases. • decreases. • remains the same. • Not enough information.

  17. Non-Free Fall CHECK YOUR ANSWER As the skydiver continues to fall faster and faster through the air, her acceleration A. increases. • decreases. • remains the same. • Not enough information. Comment If this question were asked first in the sequence of skydiver questions, many would answer it incorrectly. Would this have been you?

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