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

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Presentation on theme: "Key Concepts What factors affect the gravitational force between two objects? Why do objects accelerate during freefall?"— Presentation transcript:

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

2  Gravity  Mass  Weight  Free fall  Air resistance  Terminal velocity  projectile

3  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

4  The force of gravity acts between all objects in the universe  Any 2 objects in the universe attract each other

5  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

6  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

7  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 Mass weight gizmo

8  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

9  Near the surface of the Earth the acceleration due to gravity is 9.8m/s 2  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

10  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

11  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

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13  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?

14  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

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16  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/s 2  Goalfinder Goalfinder

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18   gravityEarthPull.gif gravityEarthPull.gif  ce.jpg ce.jpg   velocity/images/twomass.gif velocity/images/twomass.gif    content/uploads/2009/02/terminal_velocity.gif content/uploads/2009/02/terminal_velocity.gif 


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