• Why is the summer longer than winter? Because of the precession of the Earth’s axis of rotation.
• Because of the moon’s 5o inclination with respect to the Ecliptic.
• Because the Earth is rotating around its axis more slowly in the summer (→ longer days!).
• Because the Earth is closest to the sun in January and most distant from the sun in July.
• Because the Earth is closest to the sun in July and most distant from the sun in January.
A planet’s orbital period (P) squared is proportional to its average distance from the sun (a) cubed:
(Py = period in years; aAU = distance in AU)
Orbital period P known → Calculate average distance to the sun, a:
aAU = Py2/3
Average distance to the sun, a, known → Calculate orbital period P.
It takes 29.46 years for Saturn to orbit once around the sun. What is its average distance from the sun?
Think critically about Kepler’s Laws: Would you categorize his achievements as physics or mathematics?
Velocity and acceleration are directed quantities (vectors)!
Different cases of acceleration:
Acceleration in the conventional sense (i.e. increa sing speed) Deceleration (i.e. decreasing speed)
Change of the direction of motion (e.g., in circular motion)
A ball attached to a string is in a circular motion as shown. Which path will the ball follow if the string breaks at the marked point?