Transcript gravity
Gravity: an attractive force between two objects Depends on: 1. the mass of the objects 2. the distance between the 2 objects Universal Law of Gravitation: F = (G) m₁xm₂ d² The force of gravity decreases rapidly as the distance between the 2 objects increases Example: if the distance between 2 objects increases from 1 to 2 meters, the gravitational force decreases to ¼ of the original force of gravity Earth’s gravitational acceleration pulls things down at the same rate g = 9.8 m/s² F = mg Example: the gravitational force on a sky diver with a mass of 60 kg would be: F = mg = (60)(9.8 m/s²) = 588 N Weight: the gravitational force exerted on an object W = mg Mass: a measure of the amount of matter in an object Free Fall: when all forces acting on an object can be ignored Example: weightlessness On the space shuttle, gravity is still affecting the astronauts with 90% of the gravitational pull compared to us on the ground The shuttle and the astronauts are in free fall http://www.youtube.com/watch?v=iQOHRKK NNLQ http://www.youtube.com/watch?v=qnzquEO MLGU http://www.youtube.com/watch?v=pm6df_S ExVw Centripetal Acceleration: acceleration toward the center of a curved or circular path Centripetal force: the net force exerted toward the center of a curved path Example: keeps the moon in orbit For every action there is an equal and opposite reaction force Action reaction forces: are equal and in opposite directions but they are NOT balanced because they act on different objects Momentum: the product of an objects mass and velocity p = mv Example: a sprinter with a mass of 80 kg has a speed of 10 m/s, what is the runner’s momentum? p = 80kg x 10 m/s = 800 kg(m/s) 1. What is the momentum of a car with a mass of 1300 traveling at a speed of 28 m/s? 2. A baseball thrown by a pitcher has a momentum of 6 kgXm/s. If the baseball’s mass is 0.15 kg, what is the baseballs speed? 3. What is the mass of a person walking at a speed of 0.8 m/s if their momentum is 52 kgxm/s? F = (mvƒ – mv¡) t Law of conservation of momentum: the momentum of an object doesn’t change unless its mass, velocity or both change **however, it can be transferred to another object**