Forces on Earth & Moving Bodies

1. Forces on Earth & Moving Bodies Erica Ajder ERAU RET 2011

2. Bottle Demonstration • What do you think will happen when the match is lit and put to the bottle? • If you think it will move, explain which direction, how far? • Why do you think this?

3. Gravity • What is gravity? • Gravity is the force of attraction exerted between 2 celestial bodies • What 2 properties affect gravity? • Distance • Mass

4. Mass & Weight • What is the difference between mass & weight? • Mass -the amount of matter in an object based on the quantity of inertia • Weight – the force that acts upon an object usually by a celestial body

5. The Paper or the Book? • Which will hit the ground first the paper or the book? Will they land at the same time? • Explain why. • What happened?

6. The Paper or the Book Pt 2 • When dropped with the paper on top of the book, which will hit the ground first? Why? • If we put the paper under the book, which will hit the ground first? Why?

7. Feather or the Hammer? • If we dropped a hammer and a feather on Earth at the same time which would hit the ground first? Why? • If we were to do the same thing on the surface of our moon with no atmosphere, what would happen? Why?

8. Feather & Hammer Pt 2 • Watch the following video: Feather & Hammer on the Moon • Based on the video clip, what actually happened on the Moon? • What caused this?

9. Just a Cup of Water • What will happen if I take my finger off the hole in the cup? • What causes this to happen? • What will happen if I drop the cup of water in the wastebasket? Explain. • What actually happened? • Is this different than what you thought? Why?

10. Spring Scale & Mass • How much mass does the known mass have? • How many Newtons of force are exerted upon the mass? • How many Newtons of force will show on the spring scale when they are both dropped? • What happened? • Why did this happen?

11. Bodies in Motion • Explain what you think the 2 spheres will do and which will land first. • What actually happened? Why?

12. MYTHBUSTERS • Watch the following clip: • Fired vs Dropped Bullet

13. Draw the Forces Acting on Spheres Dropped Thrown T D

14. Actual Forces Acting on Spheres Dropped Thrown Velocity Thrown Force of Earth Result of forces Force of Earth D T

15. Speed, Velocity & Acceleration • Discuss with your groups and write your definition for the following thinking about how they are different in your description: • Speed • Velocity • Acceleration

16. Speed, Velocity & Acceleration • Speed– Rate of change of position using distance & time • Velocity – Rate of change of position using speed & direction • Acceleration – Rate of change of velocity change in velocity over a period of time

17. Which of the following velocity vs. time graphs represents an object with a negative constant acceleration?

18. The drawing shows the position of a rolling ball at one second intervals. Which one of the following phrases best describes the motion of this ball? • A. constant position • B. constant velocity • C. increasing velocity • D. constant acceleration

19. Concept Invention • Based on the demonstrations: • Book & Paper -1 • Cup of Water -1 • Spring Scale & Known Mass -1 • Bodies in Motion -2 • Explain the 2 over all concepts that have been discussed so far and tell the concept word if you know it. 1- concept 1 2- concept 2

20. Lab Introduction • How does gravity affect motion of objects on the Earth? • At about what acceleration do objects fall on Earth?

21. How to find distance of falling object on Earth • All falling objects accelerate at the same rate (not counting friction of air resistance). • On Earth, g ≈ 9.8 m/s2: speed increases 9.8 m/s with each second of falling. • g= gravity • The formula for the distance that something falls due to gravity is: • d= ½ g•t2 • Where: • d= distance • g= gravity • t= time

22. SIMULATION INTRODUCTION • Why do we really feel gravity? • If gravity were the only force acting on us, according to Newton’s 1st law we would always be accelerating. • The normal force (our mass pressing back down on the earth) countering gravity that gives us our everyday experience of "weight". • "Weightlessness" should really be called "Normalness".

23. We Live on a Sphere • When you drop something it heads toward the center of the Earth • If you put a bit of horizontal velocity on that something…..

24. Universal Law of Gravitation • Every mass attracts every other mass • Attraction is directly proportional to the product of their masses • Attraction is inversely proportional to the square of the distance between their centers

25. What Does All That Mean? • The simulation activities will explain how the following work: • Law of Universal Gravitation • Projectile Motion

26. Kepler’s 1st Law • The orbit of each planet around the Sun is an ellipse with the Sun at one focus. • Kepler’s 1st Law video

27. What is an ellipse? • An ellipse looks like an elongated circle or: • A circle that has been stretched in 2 directions out of shape.

28. Kepler’s 2nd Law • As a planet moves around its orbit, it sweeps out equal areas at equal times. • This means that the planet moves faster when it is closer to the sun and slower when it is further from the sun. Kepler’s 2nd Law Video The shaded parts cover the same amount of area

29. Kepler’s 3rd Law • More distant planets orbit the Sun at slower average speeds • Kepler’s 3rd Law Video T2 = Rav3 • T = orbital period in years • Rav= average distance from Sun in AU

30. Summing It All Up • The force of gravity between the Sun and a planet causes the planet to fall around the Sun (it accelerates due to gravitational force). • Because the force connects the planet and the Sun, it is not a twisting force, so the planet's angular momentum is constant: it speeds up as it gets close to the Sun, and slows down further away.