Basic Newtonian Physics

D-N Model of Scientific Explanation

S = 1000 ft

S = distance traveleda = acceleration (gravity) = 32 ft/sec/sect = time to fall (free fall)

2000 ft32 ft/sec2

= 7.9 sec

Calculating Free Fall from 1000 ft Tower

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

Reference: College Physics, Franklin Miller Jr., 2d ed., 1967

Suppose someone drops an iron bar from the top of a 1000 foot tower:

Velocity =(0 + 64000)

= 253 ft/sec

C1 = Mass 100,000 tons traveling at 80 ft/secC2 = 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.

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)

Let’s add another law:

And change the initial conditions:

Now, lets try to visualize a similar type of “collision” occurring vertically, with gravity providing the force:

Mass of Top = 100 x 1000 tons*

Mass of Base = 400 x 1000 tons*

Disconnected top falls 100 ft under force of gravity

200 ft32 ft/sec2 6.25 sec2= = 2.5 sec

Top hits Base in 2.5 seconds

Velocity =

0 + 2 x 32 ft/sec2 x 100 ft

= 80 ft/sec

v =

6400 ft/sec2Velocity of Top when it hits Base at free-fall speed after 2.5 seconds = 80 ft/second

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:

*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

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)

Mass of Top = 200 x (1000 tons)

Mass of Base = 800 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

moving at 80 ft/sec

not moving at all

L3: Newton’s First Law of Motion: A body at rest remains at rest unless it is acted upon by an unbalanced force*

*This is a recognition of inertia as an essential property of matter.

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?

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