Gravity Key Concepts What factors affect the gravitational force between two objects? Why do objects accelerate during freefall?

Key Terms Gravity Mass Weight Free fall Air resistance Terminal velocity projectile

What is gravity? Sir Isaac Newton concluded that a force acts to pull objects straight down toward the center of the Earth Gravity is a force that pulls objects toward each other

What is Universal Gravitation? The force of gravity acts between all objects in the universe Any 2 objects in the universe attract each other

What are the Factors Affecting Gravity? Two factors affect the gravitational attraction between objects: mass and distance Mass - a measure of the amount of matter in an object (atoms) SI unit of mass is kilogram - 1 kilogram is the mass of about 400 pennies = 2.2 pounds

What are the Factors Affecting Gravity? Mass – more mass an object has, the greater its gravitational force The sun’s mass is so great that it exerts a large gravitational force on the planets – One reason why they stay in orbit Distance – the farther apart two objects are, the less gravitational force between them

How are Weight and Mass related? Mass is the measure of the amount of matter in an object Weight is a measure of the gravitational force exerted on an object Weight varies with the strength of the gravitational force, but mass does not Mass weight gizmo

How does gravity affect motion? Free fall –occurs when gravity is the only force acting on an object An object in free fall is accelerating because the force of gravity is an unbalanced force

Free Fall Near the surface of the Earth the acceleration due to gravity is 9.8m/s2 For every second an object is falling its speed increases by 9.8 m/s All objects in free fall accelerate at the same rate

How does Air Resistance Affect Gravity? Objects falling through air experience a type of fluid friction called air resistance Friction is a force in the opposite direction of motion so air resistance is an upward force Falling objects with greater surface area experience more air resistance In a vacuum there is no air, all objects fall at the same rate of acceleration

How does Air Resistance Affect Gravity? Air resistance increases with velocity Eventually the falling object will fall fast enough that the upward force of air resistance will equal the downward force of gravity At this point, the forces are balanced and the objects stops accelerating The object continues to fall at constant speed This is called terminal velocity – when the force of air resistance = weight of the object

Terminal Velocity

What is Projectile Motion? Projectile - An object that is thrown Will an object that is thrown horizontally land on the ground at the same time as an object that is dropped?

What is Projectile Motion? The force of gravity still acts on the object in the same way. It falls downward at the same rate of acceleration as a ball that has been dropped

ProjectileMotion

What is Projectile Motion? If you throw an object at an upward angle, the force of gravity will reduce its vertical velocity until it stops. Then the force of gravity will pull it back to the ground When it falls it will accelerate at 9.8m/s2 Goalfinder

Sources http://www.aps.org/publications/apsnews/200510/zerogravity.cfm http://www.williamsclass.com/EighthScienceWork/ImagesEighth/gravityEarthPull.gif http://learn.uci.edu/media/OC08/11004/OC0811004_L6GravityForce.jpg http://www.melancholyrhino.com/images/gravity.jpg http://imagine.gsfc.nasa.gov/YBA/M31-velocity/images/twomass.gif http://www.daviddarling.info/encyclopedia/W/weight.html http://www.bkpc.co.uk/freefall.jpg http://leedsmathgeeks.com/wp-content/uploads/2009/02/terminal_velocity.gif http://www.mredwards.net/images/ProjectileMotion.GIF