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Chapter 3

Chapter 3. Section 2. Gravity. Gravity: Attractive force between any two objects that depends on the masses of the objects and the distance between them This force increases as the mass of either object increases The force increases as the objects move closer. Gravity.

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Chapter 3

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  1. Chapter 3 Section 2

  2. Gravity • Gravity: • Attractive force between any two objects that depends on the masses of the objects and the distance between them • This force increases as the mass of either object increases • The force increases as the objects move closer

  3. Gravity • The force between you and your textbook is weak  which is why you don’t feel it • We can feel Earth’s gravitational attraction though

  4. 4 Basic Forces • 4 Basic Forces • Gravity • Electromagnetic force  chemical interactions between atoms and molecules • Strong nuclear force  Particles in the nuclei of atoms • Weak nuclear force  Particles in the nuclei of atoms

  5. Law of Universal Gravitation • Gravitational force = constant x (mass 1)(mass 2) / (distance)2 • Constant = 6.67 x 10-11 m3/kg s2

  6. Range of Gravity • Gravitational force between two masses decreases as the distance between two objects increases • Gravitational force never completely goes to zero

  7. Gravitational Acceleration • If I drop a bowling ball and a marble at the same time which one will hit the ground first? • If air resistance is small enough to be ignored the object is in free fall • They would fall with the same acceleration • Acceleration of an object in free fall is 9.8 m/s2

  8. Gravitational Acceleration • Force of gravity (N) = mass (kg) X ( acceleration of gravity (m/s2) • Gravitational force on a sky diver with a mass of 60 kg • F = mg (60 kg) (9.8 m/s2) = 588N

  9. Weight • Gravity is pulling you down even if you are not falling • Standing on a floor the net force is zero • Weight: • Gravitational force exerted on an object • Weight (N) = mass (kg) x acceleration of gravity

  10. Weight and Mass • Weight = a force • Mass = measure of the amount of matter an object contains • Weight increases as mass increases • Weight changes depending on gravitational force

  11. Projectile Motion • Thrown objects don’t travel in straight lines • Anything that is thrown or shot through the air is called a projectile • Earth’s gravity causes projectiles to follow a curved path

  12. Horizontal and Vertical Motion • If you pitch a ball the force from your hand pushes the ball forward • No force accelerates it forward – constant horizontal force • Gravity pulls the ball downward – vertical motion • Horizontal motion: constant velocity • Vertical motion: Increasing velocity

  13. Horizontal and Vertical Distance • If you throw a ball from shoulder height would it take longer to reach the ground than if you dropped a ball from the same height? • Hit the ground at the same time • Both travel the same vertical distance • Ball thrown travels a greater horizontal distance

  14. Centripetal Force • Centripetal acceleration: • Acceleration toward the center of a curved or circular path • Centripetal force: • Net force exerted toward the center of a curved path

  15. Homework • Page 82 • 1-3 and 5-8

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