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Basic Newtonian Physics

Basic Newtonian Physics. D-N Model of Scientific Explanation. Calculating Free Fall from 1000 ft Tower. Suppose someone drops an iron bar from the top of a 1000 foot tower:. S = distance traveled a = acceleration (gravity) = 32 ft/sec/sec t = time to fall (free fall) . 2000 ft.

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Basic Newtonian Physics

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  1. Basic Newtonian Physics D-N Model of Scientific Explanation

  2. Calculating Free Fall from 1000 ft Tower Suppose someone drops an iron bar from the top of a 1000 foot tower: S = distance traveled a = acceleration (gravity) = 32 ft/sec/sec t = time to fall (free fall) 2000 ft = 7.9 sec 32 ft/sec2 Velocity = It takes 7.9 seconds for an object to fall 1000 ft under the force of gravity alone, at free fall speed—i.e., when there is no resistance underneath it—and it will be moving at 253 ft/second when it hits the ground (0 + 64000) = 253 ft/sec S = 1000 ft Reference: College Physics, Franklin Miller Jr., 2d ed., 1967

  3. Now, lets try to visualize a similar type of “collision” occurring vertically, with gravity providing the force: Let’s add another law: L3: Newton’s First Law of Motion: A body remains at rest, or if in motion it remains at uniform motion, unless it is acted upon by an unbalanced force (This is a statement of INERTIA: a body resists change in its motion) And change the initial conditions: C1 = Mass 100,000 tons traveling at 80 ft/sec C2 = Mass 400,000 tons traveling at 0 ft/sec C3 = Smaller mass collides with larger, forming a single object with a mass of 500, 000 tons Prediction: The new object will have a downward velocity due to gravity alone of 16 ft/sec if moveable*; if not, “the force of impact,” or kinetic energy, will be redistributed throughout the “parts” of the new object.

  4. Let’s suppose the top fifth of a 1000-ft vertical building loses all of its immediate support and free-falls 100 ft onto its base: Mass of Top = 100 x 1000 tons* *Let’s say the tower’s mass is 1000 tons per 100 ft; actually, the base would have to be more massive than the top to support the top’s weight Disconnected top falls 100 ft under force of gravity Top hits Base in 2.5 seconds Mass of Base = 400 x 1000 tons* 200 ft = = 6.25 sec2 2.5 sec 32 ft/sec2 v = 0 + 2 x 32 ft/sec2x 100 ft Velocity of Top when it hits Base at free-fall speed after 2.5 seconds = 80 ft/second Velocity = 6400 ft/sec2 = 80 ft/sec

  5. Mass of Top = 200 x (1000 tons) moving at 80 ft/sec L3: Newton’s First Law of Motion: A body at rest remains at rest unless it is acted upon by an unbalanced force* Mass of Base = 800 x (1000 tons) not moving at all *This is a recognition of inertia as an essential property of matter. C1 = Top of mass 100 x (1000 tons) traveling at 80 ft/sec C2 = Base of mass 400 x (1000 tons) traveling at 0 ft/sec C3 = Falling top collides with base, forming a single object with a mass of 500 x (1000 tons) Prediction: the “collapsed” Top-Base object together will have a downward velocity due to gravity of 16 ft/sec altogether if movable; if not, kinetic energy will be dissipated Question 1: Would this impact occur with enough force to pulverize concrete? Question 2: Would an iron bar at the top fall to the ground at free-fall speed? Why not?

  6. Would a sports car crashing into a parked tractor-trailer, if it could not “move” the truck, turn it into dust?

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