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https://www.youtube.com/watch?v=ttZCKAMpcAo VSV 2015 Gravity: A force of attraction Make things move….faster, slower and change direction…also gravity makes them change shape… READING: Gravity: A force of Attraction (574 – 579) Answer the 10 questions from page 579 in your notebook VSV 2015 Sir Isaac Newton VSV 2015 Why do objects fall toward the Earth, and what keeps the planets moving in the sky? https://www.youtube.com/watch ?v=jwPc0kK9VHU The law of universal gravitation describes the relationships between gravitational VSV 2015 force, mass and distance. The Law of Universal Gravitation All objects in the universe attract each other through gravitational force VSV 2015 PART 1 PART 2 VSV 2015 Distance, Mass, Fg VSV 2015 • • • • • Remember All matter has mass All matter is affected by gravity All objects experience an attraction toward all other objects Because of gravity you are being pulled right now! Why don’t you notice objects moving toward each other?. Mass is too small. VSV 2015 Weightless? (NASA pictures) VSV 2015 WEIGHT IS A MEASURE OF GRAVITATIONAL FORCE GRAVITY is a force of attraction between objects due to their VSV 2015 masses. So when gravity pulls something towards the Earth, we can call this force WEIGHT (W) W = mg VSV 2015 So when gravity pulls something towards the Earth, we can call this force WEIGHT N= (W) W = mg Kg. m S2 VSV 2015 What is “g”? 'g' is the gravitational field strength the force with which gravity pulls each kilogram of mass. W = mg w = mg W = (100 kg) (9.83 N/Kg) = mg w = (100wkg) (9.83 N/Kg) W = 100 x 9.83 N W = 983 N The force of gravity you experience due to the Earth (w) is proportional to your own mass (m). VSV 2015 apparently weightless (pictures or animation only –not a demonstration) VSV 2015 On the Moon – Apollo 15 A heavy geological hammer and a falcon feather were dropped from the same height. They hit the lunar surface at the same time. astronaut David Scott • NASA pictures http://www.youtube.com/watch?v=MJyUDpm9Kvk VSV 2015 Very heavy bootsWhy? Answers? • No gravity on the Moon • Weightless on the Moon • To stop them floating away • They weigh very much less than on Earth • To stop huge bounces • The Moon’s gravity is very much less than the Earth’s gravity VSV 2015 GRAVITY No Gravity • Things fall • Things have weight • Things stay in place Would an apple fall? Would things stay on earth? What would happen? What? Why? How? VSV 2015 VSV 2015 “If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit the ground first?” VSV 2015 VSV 2015 two objects dropped at the same time GALILEO GALILEI https://www.youtube.com/watch?v=NMM8vx9vDiE VSV 2015 https://www.youtube.com/watch?v=_mCC-68LyZM GRAVITY AND ACCELERATION Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects. VSV 2015 ACCELERATION DUE TO GRAVITY It means that every second that an object falls, the object’s downward velocity increases by 9,8 m/s² VSV 2015 All objects accelerate toward Earth at a rate of 9,8 m/s² Velocity of a falling object: ΔV=gxt ΔV = final velocity – starting velocity (m/s) g = acceleration due to gravity (9,8 m/s²) t = time the object takes to fall in seconds SOLVE MATH FOCUS EXERCISES (PAGE 591 IN YOUR COPIES) VSV 2015 VSV 2015 Net Force = 0 N A stops X X Only gravity is pulling the object down Constant velocity VSV 2015 AN ELEPHANT AND A FEATHER Suppose that an elephant and a feather are dropped off a very tall building from the same height at the same time. Which object - the elephant or the feather - will hit the ground first? VSV 2015 As air pressure decreases, the potential for air resistance also decresases. VSV 2015 WHAT’S ORBITING? AN OBJECT IS ORBITING WHEN IT IS TRAVELING AROUND ANOTHER OBJECT INTHE SPACE Orbiting and free falling VSV 2015 Launching a satellite • The cannon ball must move very quickly to orbit the earth. The Moon orbits the Earth VSV 2015 VSV 2015 THIS MOTION IS A CURVED PATH WHEN IT IS THROWN OR PROPELLED NEAR THE SURFACE OF THE EARTH MOTION PARALLEL TO THE GROUND MOTION DOWNWARD VSV 2015 HOMEWORK READING: Gravity and Motion(590 – 597) Answer the 10 questions from page 597 in your notebook VSV 2015