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Gravity, Air Resistance, Terminal Velocity, and Projectile Motion

Gravity, Air Resistance, Terminal Velocity, and Projectile Motion. A Whole Bunch of Ideas in one Show. To-Do:. Grab a study guide from the side counter and cut it in ½ to share with a partner. Do Not paste it in your journal

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Gravity, Air Resistance, Terminal Velocity, and Projectile Motion

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  1. Gravity, Air Resistance, Terminal Velocity, and Projectile Motion A Whole Bunch of Ideas in one Show

  2. To-Do: • Grab a study guide from the side counter and cut it in ½ to share with a partner. • Do Not paste it in your journal • In your whirligig groups, discuss the “Science Behind It” columnin your Deep Dive journal notes. • Discuss topics such as Gravity, Air Resistance, Mass, Force, Surface Area, Etc. • Complete the right hand side of your notes for each conclusion that you wrote.

  3. By the end of this presentation, you should be able to: • Describe and explain what is meant by terminal velocity. • Describe and explain how forces change on a falling object.

  4. What is a force • Push or pull

  5. Some basics…Draw a picture along with each fact to help you remember it! • An object’s mass _______ affect the acceleration of the object due to gravity on earth. • Friction always acts in the _________ direction as motion. • The ___________ of an object will affect the velocity of a free falling object dropping towards earth. Won’t opposite surface area

  6. What IS gravity? • Gravity is NOT “the force that pulls you down!” • Gravity attracts all objects with mass inward towards other objects with mass.

  7. the Force of Gravity • What is the force of gravity? • The force of gravity is NOT the same as the acceleration DUE to gravity!

  8. Free Fall • Objects whose only acceleration is due to gravity are in free fall. • Theoretically, objects in free fall continue to accelerate as long as they are falling. • All free falling objects accelerate at the same rate regardless of their mass. (9.8 m/s2)

  9. Galileo's Famous Experiment

  10. Acceleration of Gravity • Any object which is being acted upon only by the force of gravity is said to be in a state of free fall. There are two important motion characteristics which are true of free-falling objects: • Free-falling objects do not encounter air resistance. • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s/s (often approximated as 10 m/s/s)

  11. If the velocity and time for a free-falling object being dropped from a position of rest were tabulated, then one would note the following pattern. • Time (s) Velocity (m/s) • 0 0 • 1 - 9.8 • 2 - 19.6 • 3 - 29.4 • 4 - 39.2 • 5 - 49.0

  12. Free Fall • Newton’s 2nd Law predicts this! a = F m • The force of gravity felt by a more massive object is greater

  13. Air Resistance • Air resistance is an upward force exerted on an object as it falls by air • It is, in essence, a frictional force • For simplicity, the amount of air resistance is determined by two factors • The cross-sectional area of the object • The speed of the object

  14. Terminal Velocity Determine the acceleration of this 85 kg skydiver at points A-D. (Hint: F=ma) 9.8 m/s2 5.68 m/s2 1.56 m/s2 0 m/s2

  15. Terminal Velocity • The terminal velocity of a skydiver in a free-fall position with a semi-closed parachute is about 195 km/h • Higher speeds can be attained if the skydiver pulls in his limbs. In this case, the terminal velocity increases to about 320 km/h!

  16. The more compact and dense the object, the higher its terminal velocity will be. Typical examples are the following: raindrop, 25 ft/s, a skydiver was found to be in a range from 53 m/s to 76 m/s

  17. Possible Test Questions: • What factor causes terminal velocity to occur? • If an object is at terminal velocity, is it speeding up, slowing down, or falling at a constant speed? • Describe and explain how forces change on a falling object.

  18. W RichardsWorthing High School Terminal Velocity Consider a skydiver: • At the start of his jump the air resistance is _______ so he • ____ downwards. zero accelerates 2) As his speed increases his air resistance will _______ increase 3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY balance constant

  19. KEY Gravity (constant value & always present…weight) Air resistance (friction) Net force (acceleration OR changing velocity) How the forces change with time.

  20. Terminal Velocity Consider a skydiver: • 4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____. increases slowing down 5) Because he is slowing down his air resistance will _______ until it balances his _________. The skydiver has now reached a new, lower ________ _______. decrease weight terminal velocity

  21. Parachute opens – diver slows down Speed increases… Terminal velocity reached… On the Moon New, lower terminal velocity reached Diver hits the ground Velocity-time graph for the sky diver Velocity Time

  22. Projectile Motion • Projectile: When a falling object also experiences horizontal motion • Horizontal motion does not affect vertical motion

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