Force and Motion

1. Force and Motion

2. Gravity and Motion • Which would hit the ground first, a soccer ball or a bowling ball?

3. 400 B.C. in Greece - Aristotle “the rate at which an object falls depends on the object’s mass” Philosopher so he never tested his idea

4. 1500s in Italy – Galileo Galilei “mass of an object does not affect the time the object takes to fall to the ground”

5. Gravity and Motion • Which would hit the ground first, a soccer ball or a bowling ball?

6. They would both hit at the same time! WHY?

7. Gravity causes all objects to accelerate toward the Earth at a rate of 9.8 m/s²

8. You can calculate the change in velocity of a falling object… Equation: Δv = g x t

9. Δv = g x t • Δv = change in velocity • g = acceleration due to gravity (9.8 m/s²) • t = time

10. Practice - Δv = g x t • A penny is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen 2 seconds?

11. Practice - Δv = g x t • The same penny hits the ground in 4.5 s. What is the penny’s velocity as it hits the ground?

12. Practice - Δv = g x t • A marble is dropped from a tall building. The marble hits the ground with a velocity of 98 m/s downward. How long was the marble in the air?

13. Practice - Δv = g x t • An acorn falls from an oak tree. It hits the ground with a velocity of 14.7 m/s downward. How long did it take the acorn to land?

14. If different masses can fall at the same time, same masses definitely should!

15. Air Resistance – force that opposes the motion of objects through air Depends on: Size, Shape, and Speed of the object

16. As speed increases, so does air resistance • It continues to increase until it is equal to the downward force of gravity Gravity Force Air Resistance

17. Terminal velocity • when the object stops acceleratingbecause air resistance equals gravity Gravity Force Air Resistance

18. Terminal velocity can be a good thing • Normal terminal velocity is 5 – 40 m/s • Without air resistance, they could reach velocities near 350 m/s

19. Penny Dropped from Empire State Building Reach Speeds to Kill? • http://www.youtube.com/watch?v=PHxvMLoKRWg

20. Free Fall

21. Free fall – if only gravityand no other forces are acting on it; no place with air So where can free fall occur?

22. Freefall can occur: • In a vacuum • In space

23. In a vacuum • http://isites.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page197826&pageContentId=icb.pagecontent388782&view=watch.do&viewParam_entry=59768&state=maximize#a_icb_pagecontent388782

24. In Space • https://www.youtube.com/watch?v=KDp1tiUsZw8

25. Why is the astronaut floating inside the space shuttle? weightless?

26. Orbiting • when an object travels aroundanother object in space

27. Orbit • Caused by moving forwardand free falling

28. Projectile Motion – curved path an object follows when thrown near the surface of the earth Horizontal motion + Vertical motion Curved path

29. Projectile Motion

30. Projectile Motion

31. Projectile Motion

32. Projectile Motion

33. Projectile Motion

34. horizontal motion – parallel to the ground • vertical motion – perpendicular to the ground

35. They are independent of each other! • gravity affects only the vertical motion

36. Why is this important to know?

37. Projectile Design!!! • You will be working in groups of 5 • Create a device that will project a marble into a container 1 meter away • You will design your device and bring any items needed to make it to class tomorrow. • You will want to test it out several times and make sure it is accurate – you each get 2 shots in front of the class!

38. Ideas?