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Friday, Jan. 29 th Agenda Collect Homework: “Isaac Newton” WS Finish section 7.3: –free fall, weight, terminal velocity, Newton’s 3 rd law In-Class Assignment –Integrating Space Science, pg. 238, 4 problems Movie: “Laws of Motion” Homework: –“Gravity and the Planets” worksheet

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Homework “The Great Plague and Isaac Newton” Turn in

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Free Fall and Weight Free fall: the motion of a body when only the force of gravity is acting on it Because free-fall acceleration results from the force due to gravity, it is abbreviated by the letter g. Near Earth’s surface, g is equal to 9.8 m/s 2.

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Free-fall Acceleration near Earth’s Surface is Constant In the absence of air resistance, all objects near Earth’s surface accelerate at the same rate, no matter what their mass is. This means that if you dropped a 1.5 kg book and a 15 kg rock from the same height, they would hit the ground at the same moment.

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Weight = mass X free-fall acceleration The force on an object due to gravity is called its weight. Weight equals mass times free-fall acceleration. Weight = mass X free-fall acceleration w = m·g

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Weight = mass X free-fall acceleration Because weight is a force, the SI unit for weight is the Newton, N.

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Weight is Different from Mass Mass: the measure of the amount of matter in an object. Weight: the gravitational force an object experiences due to its mass. The weight of an object depends on gravity, so a change in an object’s location will change its weight. Remember, weight = mass X g (You will need to remember this for your in-class assignment today)

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Terminal Velocity Terminal velocity: the maximum velocity reached by a falling object that occurs when the air resistance is equal to the force of gravity. When the air resistance = the gravitational force, the object stops accelerating.

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Terminal Velocity The sky-diver reaches a terminal velocity of 320 km/hr before he opens his chute.

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Newton’s 3 rd Law Newton’s Third Law: for every action force, there is an equal and opposite reaction force. Forces always occur in pairs. The action and reaction forces act on different objects. The action and reaction forces occur at the same time.

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Newton’s 3 rd Law The upward push on the rocket equals the downward push on the exhaust gases.

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Newton’s 3 rd Law According to Newton’s third law, the soccer ball and the foot exert equal and opposite forces on one another.

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In-Class Assignment Integrating Space Science, pg. 238 Use the equation weight = mass X g to find the weight of a 58 kg person on Earth, Mars, Venus, and Neptune.

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Movie “Laws of Motion”

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Homework “Gravity and the Planets” worksheet Be ready for a quiz covering section 7.3 next time!

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