Topic 3

Galileo: Return to Earth

Aristotle BC 384-322

Four Elements

• Earth

• Water

• Air

• Fire

• Aether

Natural Motion:

Elements tend to seek their natural place.

Violent Motion:

Any forced motion that opposes natural motion.

(Push or Pull)

The speed of a moving object is directly proportional to the force moving it.

Aristotle’s Laws of Motion

1. Rest is the natural state of an object.

2. Heavier things fall faster, the speed proportional to the weight.

Some definitions:

• Displacement= distance the object covers and the direction it came from…

• Velocity= change in displacement in time

(note: it is speed AND direction)

• Speed is only how fast the object moves

• Acceleration= change in velocity in time.

Galileo Galilei (1564-1642)

Two New Sciences

Aristotle’s fall

Galileo’s fall

A thought experiment

• GIVEN: three identical weights dropped from the same height

Does a ten pound weight fall ten times faster than a one pound

weight?

                               

Can Galileo measure free fall?

Dilute the process

S:\dowshep.mid

Galileo observed

• D1 = 1 D1

• D2 = 3 D1

• D3 = 5 D1

• D4 = 7 D1

Galileo observed

Note increasing Velocity

Does it really work? Distance time (time)2 d/t d/t2

150.00 1.00 1.00   150.00 150.00

125.00 0.91 0.83   137.36 150.95

100.00 0.81 0.66   123.46 152.42

75.00 0.70 0.49   107.14 153.06

50.00 0.57 0.32   87.72 153.89

Our results

Velocity vs time

0.00

50.00

100.00

150.00

200.00

1.00 0.91 0.81 0.70 0.57

time (sec)

Ve

loc

ity

(c

m/s

ec

)

Acceleration vs time

100.00

120.00

140.00

160.00

180.00

200.00

1.00 0.91 0.81 0.70 0.57

time (sec)accele

rati

on

(cm

/sec/s

ec)

2 ramps?

• Rest was not a natural state.

• The concept of inertia was introduced.