1. STARTER Galileo Galilei was an Italian physicist, mathematician, engineer, astronomer, and philosopher who played a major role in the scientific revolution. He proposed that all falling bodies/objects accelerate uniformly. Meaning if I dropped a bowling ball and a golf ball from the rooftop they will hit the earth at the same time. Is this true? Why or why not?

2. GRAVITY, AIR RESISTANCE AND TERMINAL VELOCITY DAY 19

3. MINI-LAB Questions Pre-Lab Questions 1.If you drop the two objects from the same height, will they hit the floor at the same time? 2.Does the mass or weight of the object have an effect on how fast the object falls?

4. MINI-LAB Questions Post-Lab Questions 1.What does gravity mean to you? 2.Is gravity a weak force or a small force? Think before you answer? 3.How do you know that there is gravity on Earth?

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/s 2 ) All free falling objects accelerate at the same rate regardless of their mass.

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 2 (often approximated as 10 m/s 2 )

11. FREE FALL

12. 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

13. TERMINAL VELOCITY Determine the acceleration of this 85 kg skydiver at points A-D. (Hint: F=ma) 9.8 m/s 2 5.68 m/s 2 1.56 m/s 2 0 m/s 2

14. TERMINAL VELOCITY The terminal velocity of a skydiver in a free-fall position with a semi-closed parachute is about 195 km/hr. Higher speeds can be attained if the skydiver pulls in his limbs. In this case, the terminal velocity increases to about 320 km/hr! The more compact and dense the object, the higher its terminal velocity will be.

15. 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.

16. TERMINAL VELOCITY Consider a skydiver: 1)At the start of his jump the air resistance is _______ so he ________ downwards. 2 ) As his speed increases his air resistance will _______ 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 zero accelerates increase balance constant

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

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

19. EXIT SLIP Must turn in lab! With questions answered correctly.