Starter 11/15 In your spiral notebook…Provide answers to these three questions:

1. LT 1 I can calculate how fast, how far and how long an object will fall, neglecting air resistance. LT 2 I can explain why all objects, neglecting air resistance, fall at the same rate. LT 3 I can explain freefall and identify when terminal velocity occurs for falling objects. LT 4 I can explain the two factors that influence the amount of air resistance a falling object experiences, and analyze the forces interacting on a falling object to determine its motion.

2. Starter 11/15 In your spiral notebook…Provide answers to these three questions: 1. Describe the Earth’s atmosphere. 2. Describe air resistance 3. Describe the term aerodynamic shape.

3. Earth’s Atmosphere Major Constituents • Nitrogen (N2) 78% • Oxygen (O2) 21% • Argon (Ar) < 1% Minor Constituents Water vapor (H2O) Carbon dioxide (CO2) Methane (CH4) Nitrous oxide (N2O)

4. Without the Ozone Layer • No terrestrial life (UV rays are dangerous to life: DNA destroyed for example) Temperature fluctuation

6. Atmospheric Layers • Four Layers • Thermosphere (outermost layer, receives intense solar radiation) • Mesosphere (coldest layer) • Stratosphere (contains the ozone layer, warmer due to absorption of ultra-violet light) • Troposphere (the weather layer, the densest layer) • Also, the Ionosphere (forms due to the interaction of cosmic radiation from the Sun with the faint nitrogen and oxygen concentration in the thermosphere)

7. AIR RESISTANCE A resistance force caused by air molecules opposing the motion of an object as it moves through the air. A form of friction sometimes called drag. Aerodynamic shape

8. AIR DENSITY

9. AIR DENSITY Less drag More drag

10. Suppose a bowling ball is falling… How many forces are acting on it? 2 Air Resistance Force Gravitational force The weight of the bowling ball is the same as the gravitational force acting on the ball (reported in Newtons)

11. Free Fall An object moving only under the influence of the gravitational force is in free fall. The acceleration of an object in free fall on Earth is 9.8 m/s2. For free fall, neglect air resistance!

12. Free Fall Free body diagram Only under the influence of gravitational force. No air resistance force! This object will continue to gain speed at a rate of 9.8 m/s2. Rock that weighs 100 N Fgrav = 100 N

13. The acceleration of an object in free fall is 9.8 m/s2. 4.5-4.6Free Fall Neglecting air resistance!

14. Free Fall: How Fast During each second of fall the speed of by the object increases by an additional 9.8 meters per second. V = gt This gain in speed per second is the acceleration. After 1 second = 9.8 m/s After 2 seconds = 9.8 m/s x 2 After 3 seconds = 9.8 m/s x 3… and so on

15. 4.5Free Fall: How Fast v = gt v represents both speed and velocity. g represents acceleration due to gravity (9.8 m/s2) t represents time the object is free-falling

16. 4.5Free Fall: How Fast 9.8 m/s 19.6 m/s 29.4 m/s 39.2 m/s 49 m/s 9.8 m/s x t

17. Rising Objects Free Fall: How Fast Rising objects decelerate at the same rate that falling objects accelerate. During the upward part of this motion, the object slows from its initial upward velocity to zero velocity. The object decreasesin speed at the same rate that it increases in speed as it rises and falls

18. 4.5Free Fall: How Fast Rising Objects Rising objects decelerate at the same rate that falling objects accelerate. During the upward part of this motion, the object slows from its initial upward velocity to zero velocity. The object is accelerating because its velocity is changing. How much does its speed decrease each second?

19. Air Resistance and Falling Objects Drop a feather and a hammer on earth and the hammer reaches the floor far ahead of the feather. What about on the Moon? (see video clips in class)

20. 4.8Air Resistance and Falling Objects A feather and a coin accelerate equally when there is no air around them. Vacuum tube

21. 4.8Air Resistance and Falling Objects F gravity or weight is the only force How objects fall without air resistance?

22. 4.8Air Resistance and Falling Objects F gravity or weight is the only force How objects fall without air resistance? Objects accelerate equally. Why? No atmosphere means no air resistance (no drag force), so surface area and weight make no difference. All objects fall at the same rate. Moon It’s just like on the __________________

23. 4.8Air Resistance and Falling Objects Drop a feather and a hammer on earth and the hammer reaches the floor far ahead of the feather. What about on the Moon? http://history.nasa.gov/40thann/videos.htm

24. 6.6Free Fall Explained In Galileo’s famous demonstration, a 10-kg cannonball and a 1-kg stone strike the ground at practically the same time. This experiment demolished the Aristotelian idea that an object that weighs ten times as much as another should fall ten times faster than the lighter object.

25. g = weight/mass a = force/mass 6.6Free Fall Explained F stands for the force (or weight in newtons) m stands for the mass of the cannonball a is the rate of acceleration • the weight-to-mass ratio is the same for these or any objects, which means that the acceleration rates are the same. 10x gravitational force or weight 1 kg rock 10 kg cannonball

26. 6.6Free Fall Explained Since the ratio of weight (F) to mass (m) is the same for the 10-kg cannonball and the 1-kg stone, they both fall at the same rate of acceleration. Why?

27. 6.6Free Fall Explained Since the ratio of weight (F) to mass (m) is the same for the 10-kg cannonball and the 1-kg stone, they both fall at the same rate of acceleration. Why? Weight-mass ratios for each are identical! It takes a larger force to keep the larger mass accelerating because a larger mass has more inertia.

28. 6.6Free Fall Explained All freely falling objects fall with the same acceleration because the ratio of weight to mass is the same for all objects.

29. Free Fall An object is said to be in free fall if it is only under the influence of gravitational force. This object will fall at a rate of acceleration equal to 9.8 m/s2. No support or resistance force! Fg = 100 N

30. Free Fall Physicists consider air resistance to be negligible for heavier objects that fall near the surface of the Earth. Don’t worry about air when making calculations! Fg = 71.2 N Fg = 11 N Fg = 100 N

31. Air resistance does not depend upon the weight of the object. 6.7Falling and Air Resistance The amount of air resistance force an object experiences depends on the object’s speed and exposed surface area. 1. Speed The greater the speed, the greater the air resistance. 2. Surface Area (exposed or frontal) The greater the surface area, the greater the air resistance.

32. Falling and Air Resistance What two factors determine the air resistance force on an object? The speed and the exposed surface area

33. AIR RESISTANCE • A resistance force caused by air molecules opposing the motion of an object as it moves through the air. • A form of friction sometimes called drag.

34. Another variable… • How would the composition or density of an atmosphere influence air resistance? • More density, more air resistance!

35. 4.6Free Fall: How Far For each second of free fall, an object falls a greater distance than it did in the previous second.

36. 4.6Free Fall: How Far These distances form a mathematical pattern: at the end of time t, the object starting from rest falls a distance d.

37. 4.6Free Fall: How Far 4.9 m 19.6 m 44.1 m 78.4 m 122.5 m

38. 4.6Free Fall: How Far For a falling object, how does the distance per second change? For each second of free fall, an object falls a greater distance than it did in the previous second.