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PHYSICAL SCIENCE

PHYSICAL SCIENCE. Chapter 3 Forces 3.2 Gravity. 3.2 Gravity Objectives. Describe the gravitational force. Distinguish between mass and weight. Explain why objects that are thrown will follow a curved path. Compare circular motion with motion in a straight line. What is Gravity.

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PHYSICAL SCIENCE

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  1. PHYSICAL SCIENCE Chapter 3 Forces 3.2 Gravity

  2. 3.2 Gravity Objectives • Describe the gravitational force. • Distinguish between mass and weight. • Explain why objects that are thrown will follow a curved path. • Compare circular motion with motion in a straight line.

  3. What is Gravity • Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them. • As the mass of either object increases, so does the gravitational force between them. • Gravitational force between two objects increase as the distance between them decreases.

  4. What is Gravity • Gravity is one of the four basic forces… • Gravity • Electromagnetic force • Strong force • Weak force http://scienceblogs.com/startswithabang/2012/06/27/the-strong-force-for-beginners/ http://mail.colonial.net/~hkaiter/Gravity_Inertia.html

  5. The Law of Universal Gravitation • The Law of Universal Gravitation by Sir Isaac Newton, 1687 gravitational force = (constant) • (mass 1) • (mass 2) (distance)2

  6. The Law of Universal Gravitation • “F” is the force of gravity. • “G” is a constant called the universal gravitational constant. • “m1” and “m2” are the masses. • “d” is the distance between the two masses. • Gravity is a long range force that gives the universe its structure. • Gravitational force never completely goes to 0 between any two objects.

  7. The Law of Universal Gravitation • In the 1840s, the most distant planet known was Uranus. • The observed motion of Uranus and the calculated motion of Uranus according to the law of universal gravitation differed slightly. • Some astronomers attributed this to an undiscovered planet. • Two astronomers independently calculated the orbit of this undiscovered planet and, as a result, Neptune was discovered in 1846.

  8. http://imgarcade.com/1/king-neptune-drawing/

  9. http://universeandplanets.blogspot.com/2011/07/neptune-planet.htmlhttp://universeandplanets.blogspot.com/2011/07/neptune-planet.html

  10. Earth’s Gravitational Acceleration • Due to inertia, all objects fall with the same acceleration regardless of mass. • Close to Earth’s surface, the acceleration of a falling object in free fall is about 9.8 m/s2. • This acceleration constant is sometimes given the symbol “g” and called the acceleration of gravity. force of gravity (N) = mass (kg) x acceleration of gravity (m/s2) F=mg • The gravitational force on a skydiver with a mass of 60 kg would be…. F = mg = (60 kg)•(9.8 m/s2) = 588 N

  11. Earth’s Gravitational Acceleration • Mass is a measure of the amount of matter in an object and weight is the gravitational force of attraction exerted on an object. • Acceleration of gravity on the Moon is 1.6 m/s2 – about 1/6th as large as Earth’s gravitational acceleration. http://science.nasa.gov/science-news/science-at-nasa/2009/17jul_discoveringearth/

  12. Weightlessness and Free Fall • Typical shuttle mission orbits Earth at an altitude of about 400 km. • At 400 km, the force of Earth’s gravity is about 90% as strong as it is at Earth’s surface. • A space shuttle in orbit is in free fall, but it is falling around Earth instead of straight down. • Everything in the shuttle is falling around Earth at the same rate as the shuttle itself. • This creates the sensation of weightlessness. • Next slide - http://hrsbstaff.ednet.ns.ca/jenninj2/Physics%2012/Gravitation/universal_gravitation.htm

  13. Projectile Motion • Projectiles don’t travel in straight lines, their path curves downward due to gravity. • The force we exert on a thrown ball gives it horizontal motion. • After the ball is released, no force accelerates it forward, so its horizontal velocity is constant (excluding air resistance). • When the ball is released, gravity pulls it downward, giving it vertical motion.

  14. Projectile Motion • Now the ball has constant horizontal velocity, but increasing vertical velocity. • Gravity exerts an unbalanced force on the ball, changing the direction of its path from only forward to forward and downward. • Thrown ball and dropped one hit the ground at the same time. • Both balls travel the same vertical distance in the same amount of time, though the thrown ball travels a greater horizontal distance than the dropped ball.

  15. Centripetal Force • Acceleration toward the center of a curved or circular path is called centripetal acceleration. • The net force exerted toward the center of a curved path is called a centripetal force. • Anything that moves in a circle is doing so because a centripetal force is accelerating it toward the center. • Earth’s gravity exerts a centripetal force on the Moon that keeps it moving in a near circular orbit.

  16. Video Links • Brian Cox visits the world's biggest vacuum chamber - Human Universe: Episode 4 Preview - BBC Two (4:41) - https://youtu.be/E43-CfukEgs • Zero Gravity Flight - Weightlessness (4:58) - https://youtu.be/HQbAwE83phk

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