2. What are we learning about today? What are we learning about today?

3. Gravity What is it? https://www.youtube.com/watch?v=mezkHBPLZ4A

4. Gravity is … A natural force that pulls all objects toward the center of the earth. A natural force that pulls all objects toward the center of the earth. http://www.neok12.com/video/Gravitatio n/zX64676359061f6b43074555.htm

5. WHAT IS A FORCE? A pull or a push on an object It is measured in Newtons (N) or kg/ m/ s 2.

6. Newton was a Smart Guy Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.

7. 1 st law: An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force. Things will keep moving forever unless it is stopped by a force. Things will stay stationary (in one place) unless an outside force acts on it. If a golf ball was hit in space would it stop? If a golf ball was hit in space would it stop? If a golf ball was hit on Earth, would it to stop? What causes is to stop? If a golf ball was hit on Earth, would it to stop? What causes is to stop? Earth’s Gravity causes things to stop. The opposing force that occurs by making contact with another object is called Friction http://www.sciencechannel.com/games-and- interactives/newtons-laws-of-motion-interactive/ http://www.sciencechannel.com/games-and- interactives/newtons-laws-of-motion-interactive/ http://www.sciencechannel.com/games-and- interactives/newtons-laws-of-motion-interactive/ http://www.sciencechannel.com/games-and- interactives/newtons-laws-of-motion-interactive/

8. Friction: a force that opposes the motion of objects that touch as they move past each other. Friction: a force that opposes the motion of objects that touch as they move past each other. Without friction, the world would be a very different place. In a frictionless world, every surface would be more slippery than a sheet of ice. Without friction, the world would be a very different place. In a frictionless world, every surface would be more slippery than a sheet of ice. Your food would slide off your fork. Walking would be impossible. Your food would slide off your fork. Walking would be impossible. Cars would slide around Cars would slide around helplessly with their wheels spinning. Magic School Bus Clip Magic School Bus Clip

9. Some Examples from Real Life Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion. A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

10. Newton’s First Law is also called the Law of Inertia Inertia: the tendency of an object to resist changes in its state of motion The First Law states that all objects have inertia. ***The more mass an object has, the more inertia it has (and the harder it is to change its motion). http://www.nbclearn.com/nhl/cuecard/56615

11. More Examples from Real Life A powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them. On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).

12. 2 nd law: Force equals mass times acceleration. This equation helps teach us that Gravity is a force. This equation helps teach us that Gravity is a force. Acceleration is how quickly an object is changing speed Acceleration is how quickly an object is changing speed Earth’s gravity has a constant acceleration downward. All objects accelerate at 9.8 m/s 2. Earth’s gravity has a constant acceleration downward. All objects accelerate at 9.8 m/s 2. If we all jumped out of a plane we would fall at 9.8 m/s 2. This goes for all other objects whether large or small. If we all jumped out of a plane we would fall at 9.8 m/s 2. This goes for all other objects whether large or small.

13. Which do you think would fall first? A bouncy ball A bouncy ball Or a marble Try It! http://indianapublicmedia.org/amomentofs cience/ground-golf-bowling-ball/

14. They fall at the same rate of speed, because of Earth’s constant downward acceleration. But the marble has more mass (weight) and so gravity makes it fall harder and hits the earth with more force! Gravity has a stronger force on things with more mass!

15. It takes force to overcome gravity! Throw a bean bag in the air and then… Throw a basketball in the air. Which one was harder to throw? The basketball would be harder to throw. You had to use more force to throw the basketball because it has more mass (weight) The basketball would be harder to throw. You had to use more force to throw the basketball because it has more mass (weight)

16. What does F = ma say? F = ma basically means that the force of an object comes from its mass and its acceleration. Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force. Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.

17. Using Force = mass x acceleration Calculate which would land with more force: Calculate which would land with more force: Object 1 has a mass of 20 grams Object 1 has a mass of 20 grams Object 2 has a mass of 100 grams Object 2 has a mass of 100 grams Acceleration is 9.8 m/s 2. Acceleration is 9.8 m/s 2. Force of Object 1? Force of Object 1? Force of Object 2? Force of Object 2? http://www.pbs.org/opb/circus/classroom/circus-physics/activity- guide-newtons-laws-motion/

18. 3 rd Law: For every action there is an equal and opposite reaction. ~ For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up. http://www.pbs.org/opb/circus/classroom/circus- physics/activity-guide-newtons-laws-motion/ http://www.pbs.org/opb/circus/classroom/circus- physics/activity-guide-newtons-laws-motion/ http://www.pbs.org/opb/circus/classroom/circus- physics/activity-guide-newtons-laws-motion/ http://www.pbs.org/opb/circus/classroom/circus- physics/activity-guide-newtons-laws-motion/

19. Think about it... What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts). http://www.quia.com/quiz/1321898.html

20. Satellites move fast enough that they overcome earth’s gravitational pull, but still stay within the earth’s orbit. As you know Satellites move around our earth. But did you know that is a problem? As you know Satellites move around our earth. But did you know that is a problem?

21. “There are currently over eight thousand satellites and other large objects in orbit around the Earth, and there are countless smaller pieces of debris generated by spacecraft explosions and by collisions between satellites. Until recently, it has been standard practice to put a satellite into orbit and leave it there. However, the number of satellites has grown quickly, and as a result, the amount of orbital debris is growing rapidly. Because this debris is travelling at orbital speeds (7-8 km/s!), it poses a significant threat to the space shuttle, the International Space Station, and the many satellites in Earth orbit.” “There are currently over eight thousand satellites and other large objects in orbit around the Earth, and there are countless smaller pieces of debris generated by spacecraft explosions and by collisions between satellites. Until recently, it has been standard practice to put a satellite into orbit and leave it there. However, the number of satellites has grown quickly, and as a result, the amount of orbital debris is growing rapidly. Because this debris is travelling at orbital speeds (7-8 km/s!), it poses a significant threat to the space shuttle, the International Space Station, and the many satellites in Earth orbit.” http://images.google.com/imgres?imgurl=http://www.tethers.com/W ebImages/OrbitalDebris.jpg&imgrefurl=http://www.tethers.com/Orbit alDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=250&w=2 58&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&tbnh=109&tb nw=112&prev=/images%3Fq%3Dearth%2B%252B%2Bsatellites%26 gbv%3D2%26hl%3Den%26safe%3Dactive http://images.google.com/imgres?imgurl=http://www.tethers.com/W ebImages/OrbitalDebris.jpg&imgrefurl=http://www.tethers.com/Orbit alDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=250&w=2 58&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&tbnh=109&tb nw=112&prev=/images%3Fq%3Dearth%2B%252B%2Bsatellites%26 gbv%3D2%26hl%3Den%26safe%3Dactive

22. When do Satellites become subject to earth’s gravity? The cannon ball must move very quickly to orbit the earth. If an object does not meet the required speed it would be slowly dragged into the Earth’s atmosphere. * Objects farther from earth experience less gravitational pull. The closer to earth’s surface the more gravitational pull is felt.

23. The Moon orbits the Earth and is therefore a Satellite. Despite that the moon is much farther it is still attracted to the Earth’s gravitational pull, but it moves so quickly it revolves the planet at a fixed distance. Despite that the moon is much farther it is still attracted to the Earth’s gravitational pull, but it moves so quickly it revolves the planet at a fixed distance.

24. The Moon is also 1/16 the size of the earth and therefore has 1/16 of the gravitational pull. Earth’s gravity is 9.8 m/s 2. Moon’s gravity is.1625 m/s2.

25. State Objectives… Distinguish between mass and weight… Mass: the amount of matter in an object Mass: the amount of matter in an object Weight: the force of gravity acting on an object Weight: the force of gravity acting on an object How is weight determined? How is weight determined? Scales Scales

26. If you went to Mars would you mass be the same or different? If you went to Mars would you mass be the same or different?SAME If you went to Mars would If you went to Mars would you weight be the same you weight be the same or different? Different

27. Cite examples of how Earth’s gravitational force on an object depends upon the mass of the object. Moon Satellites Both have less mass than Earth and therefore are pulled in by Earth’s gravity

28. Describe how Earth’s gravitational force on an object depends upon the distance of the object from Earth. Describe how Earth’s gravitational force on an object depends upon the distance of the object from Earth. Moon vs. Mars Moon vs. Mars