chapter 2 continuation... thursday, january 24 spring 2008
TRANSCRIPT
Chapter 2 continuation...
Thursday, January 24
Spring 2008
Tycho Brahe’s view on planetary motion
Tycho Brahe (1546 – 1601)
The last great naked-eye astronomer
(telescopes did not exist while he was alive)
Constructed a large quadrant to make highly
accurate measurements of the positions of the planets
and stars
The Tychonic System
Tycho Brahe combined the geocentric and
heliocentric systems of the universe into his
own model, the “Tychonic System”
Kepler and the laws of planetary motion
Johannes Kepler (1571 – 1630)
Publicly defends the Copernican system in his first major astronomical work, The
Sacred Mystery of the Cosmos.
Begins work as an assistant to Tycho Brahe in Prague in 1600, analyzing Tycho’s planetary observation data.
Inherits Tycho Brahe’s data after Brahe’s death in 1601.
Kepler’s laws of planetary motion
T 2
r 3constant
(for all planets orbiting the sun)
=
Kepler’s 1st Law: Kepler’s 2nd Law:
Kepler’s 3rd Law :
T = period of orbit
r = orbital radius
Shortly after the invention of the telescope, Galileo made several observations that could not be accounted for by the geocentric system
Galileo and Planetary Motion
Galileo Galilei (1564 – 1642)
Galileo and Planetary Motion
• Galileo observed the moon “...to be uneven, rough, and crowded with depressions and bulges. And it is like the face of the earth itself, which is marked here and there with chains of mountains and depths of valleys.”
• He discovered four moons orbiting the planet Jupiter.
• He observed the phases of the planet Venus.
• He observed sunspots.
Galileo’s Views on Motion
vv
On a sloped surface, a ball rolling down
the slope gains speed, while a ball rolling up the slope
loses speed.
On a flat surface, there is no slope to
cause a rolling ball to slow down or speed up... it continues its
motion forever.
Principle of inertia: constant-speed, straight-line motion is as natural as at-rest motion.
Describing Motion
• speed is distance traveled over time (a scalar)
• velocity is speed with direction (a vector) – velocity is displacement, D, over time
• acceleration is the rate of change of velocity (a vector)
s = d / t
v = D / t
a = (vf – vi) / t
Galileo and the Inclined Plane
Galileo and the Motion of Falling Objects
t (s) d (m) v (m/s)
0
0
1
1
2
4
3
9
4
16
5
25
6
36
1
3
5
7
9
11
Acceleration of falling objects found to be constant:
a = (vf – vi) / t = 2 m/s2 at all time points in Fig. 2-7
Finish reading Chapter 2 in the textbook for next
Tuesday 01/29
Mallard HW quiz for Chapter 2 now available
– due next Thursday 01/31