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Published byWalter Pope Modified over 6 years ago

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Physical Science Gravity

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Objectives Explain that gravitational force becomes stronger as the masses increase and rapidly become weaker as the distance between the masses increases, F=G(m 1 m 2 /d 2 ) Evaluate the concept that free-fall acceleration near Earth’s surface is independent of the mass of the falling object Demonstrate mathematically how free-fall acceleration relates to weight Describe orbital motion as a combination of two motions

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The law of universal gravitation: –All objects in the universe attract each other through gravitational force (Sir Isaac Newton 1642-1727) –Universal Gravitation Equation F=G(m 1 m 2 /d 2 )

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Gravitational force increases as one or both masses increases Gravitational distance decreases as the distance between the masses increases G is a constant –If the distance between two objects is doubled, the gravitational force between them decreases to ¼ the original value –If distance is tripled, gravitational force decreases by 1/9 the original value

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Free Fall Free fall- the motion of body when only the force of gravity is acting on the body Free fall results from gravity= g~ 9.8m/s 2 Free fall acceleration of an object is directed toward the center of Earth

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In a vacuum (an absence of air resistance) a feather and an apple accelerate at the same rate regardless of mass. Why? Newton’s second law of motion (acceleration depends on both force and mass)

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Weight- the force on an object due to gravity Weight is equal to mass times free-fall acceleration Weight=mass x free-fall acceleration w= mg

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Weight is a force, the SI unit of weight is the newton, N. w=mg Ex) 1.0kg x 9.8m/s 2 = 9.8 N

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*Recall the difference between mass and weight Mass is the measure of the amount of matter in an object (this does not change) Weight changes as gravitational force changes

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Space Planets in our solar system have different diameters and different masses. Therefore each planet has a unique value for g. Earth, g= 9.8m/s 2 Venus, g= 8.8m/s 2 Mars, g= 3.7m/s 2 Neptune, g= 11.8m/s 2

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Velocity and air resistance A falling object stops accelerating when the force of air resistance = the gravitational force on an object (the weight) Terminal velocity- the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

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Free Fall An object is in free fall only if gravity is pulling it down and no other forces are acting on it Free fall can only occur in a vacuum- no air and no matter, or in space Orbiting objects are in free fall

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Orbiting Two motions combine to cause orbiting Orbiting- when an object is traveling in a circular or nearly circular path around another object Linear motion forward + downward pull of gravity = curve of Earths surface

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Projectile motion Two motions combine to form projectile motion Projectile motion- the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth; the motion of objects that are moving in 2-D under the influence of gravity

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Projectile motion Horizontal velocity + vertical downward pull of gravity= curved path The two velocities are independent of each other

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