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Gravity
• Gravity is the force that pulls objects toward the center of the earth.
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Gravity
• But…it goes beyond just that…….
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Gravity
• Newton’s greatest discovery!
• The Law of Universal Gravitation.– Every mass attracts every other mass with a
force that is proportional to the product of the two interacting masses
– Force ~ (mass1 x mass2) / distance2
– Force decreases with the inverse square of distance
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Gravity
• Free fall is when the only force acting on an object is gravity.
• All objects in free fall accelerate at the same rate regardless of mass
• Demos
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Gravity
• Fluid friction in the air is called “Air Resistance”
• In air, an object in free fall will continue to accelerate until the force of air resistance equals the force applied due to gravity.
• The greatest velocity of a free fall object in air is called “Terminal Velocity”
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Gravity
• Weight is the measure of the force of gravity on an object.
• Mass is a measure of the amount of matter in that object
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Gravity
• Weight is expressed with the equation:
• Newtons(N) = mass x acceleration due to gravity.
• 1N = 1Kg x 1 m/sec2
• 9.8N = 1Kg x 9.8m/sec2
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Gravity
• Example:– A 100Kg person weighs……..– (N) = mass x acceleration due to gravity– 100kg x 9.8m/s2
– So…….a 100Kg person weighs 980N on the Earth’s surface
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Gravity
• Potential Energy is the energy an object has because of it’s position in a force field, such as a gravitational field.
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Gravity
• Gravitational Potential Energy (GPE)= Weight x Height
• GPE is expressed as Newton Meters Nm.
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Gravity
• Since we know that weight = mass x acceleration due to gravity.
• Logically……..
• GPE = mgh (mass x Acceleration due to gravity x height)
• Demo..penny shot
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Gravity
• As an object falls, it’s GPE turns into……
• Kinetic Energy, the Energy of motion
• Kinetic Energy(KE) = 1/2 mass x velocity2
• KE = 1/2mv2
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Not really Gravity….Oh well!
• Momentum is the product of a objects mass and its velocity.
• Momentum = Mass x velocity
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Not really Gravity….Oh well!
• Conservation of Momentum– The total momentum of any group of objects
remains the same unless outside forces act on the objects.