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NEWTON’S 2 nd Law of Motion

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Newton’s 2 nd law of Motion Describes the relationship of how something with a mass accelerates when it is pushed/pulled by a force. Force Acceleration

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Newton’s 2 nd law of Motion An object will accelerate in the direction of a net force. Force Acceleration

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Is the direction of the motion of the object always the same as the direction of the acceleration? 1.Yes 2.No

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F = ma Net Force mass acceleration

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F= ma Song

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Units F = m·a = kg·m/s 2 = kg·m/s 2 = Newton = Newton

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Example For a while, the National Marbles Tournament was, as one newspaper put it in 1925, "the highest honor possible in the sporting world for (kids).” The game of marbles was a highly competitive game from the early 1900’s to late 1960’s in the United States. The game of marbles was played by propelling a marble with the thumb to hit another marble as to drive it out of a circle VFW National Champ Tilton "Pork Chop" Holt in action at the Eaton Rapids, Michigan finals. From LIFE Magazine, June 26, 1950

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Example (cont.) “Pork Chop” Holt flicks.036 kg marble at an acceleration of 7.2 m/s 2. What force did he use to propel his marble?

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EXAMPLE The Inuit people of the Arctic region, one of the most forbidding territories on Earth, have an economy that revolves around the changing seasons and the animals that could be successfully hunted during these periods. Assume an that an Inuit has caught a sled full of salmon. If he pulls the sled with a force of 80 N and the sled has a mass of 87kg, what is the acceleration of the sled as he pulls it a short distance across the snow?

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Example A 15 kg object is being pulled upwards by a force of 3 N and to the left by 4 N. What is the objects acceleration? a = ? m = 15 kg F net = 5 N 4 N 3 N a = F net / m = 5 N / 15 kg = 0.33 m/s 2

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Application of Newton’s 2 nd Law: Weight & mass

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Does your mass change on the moon? 1.Yes 2.No

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How would the size of these forces change on the moon?

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WHY?

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What things affect weight? AND

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F w = mg Weight (N) Acceleration caused by gravity (m/s 2 ) Mass (kg)

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What’s your mass? Convert pounds into kilograms. What’s your weight in Newtons (on the EARTH)? 9.8 m/s 2 F w = mg

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Calculate the following using your information: mass = ____ kg weight = ____ lbs weight = ____ N mass = ____ kg weight = ____ lbs weight = ____ N mass = ____ kg weight = ____ lbs weight = ____ N EarthJupiter Moon g = 9.8 m/s 2 g = 1.6 m/s 2 g = 26 m/s 2

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How does this apply to falling objects?

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A closer look at free-fall (WITH AIR RESISTANCE) m = 100 kg Weight Air resistance If force due to air resistance was 400 N, what is the object’s acceleration?

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What is happening to the speed of the previous object? 1.It is speeding up 2.It is slowing down 3.It is staying the same.

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Terminal Velocity When an object in free-fall is no longer accelerating m = 100 kg Air resistance Weight

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A challenge!

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What is the force? If I drag my book across the table with a 3 N force at a CONSTANT VELOCITY, what is the force of friction? Force pulling = 3 N Force of friction = ? a = F net =

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What is the force? If I drag my 1.5 kg book across the table with a 3 N force and it accelerates at a rate of 1.1 m/s 2, what is the force of friction? Force pulling = 3 N Force of friction = ? a = 1.1 m/s 2 F net = 1.5 kg

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