Class Notes (808,147)
Chemistry (1,118)
CHEM 222 (112)
Lecture

# epsc 200 chapter 7 notes.docx

5 Pages
62 Views

School
McGill University
Department
Chemistry
Course
CHEM 222
Professor
Karine Auclair
Semester
Winter

Description
7. Rotational Dynamics of the Planets and their Satellites - Planets rotate on their own axes (as do the moons of the planets) - The Earth wobbles as it rotates • Partly due to the seasonal movement of mass over the Earth (seasonal wobble) - The Moon librates (swings back and forth) as it orbits the Earth Key Points: - Jupiter rotates fastest - Venus rotates slowest - Venus, Uranus, and Pluto are inclined more than 90 to their orbital plane. - Pluto and Uranus rotate with their axes lying almost in their orbital plane - Venus has highest inclination angle (it rotates backwards in relation to its revolution about the Sun 7.1 Moments of Inertia of the Planets - A rotating body tends to stay in rotation unless acted upon by an external torque. - Angular Momentum ( ) = The quality and quantity which determines the continuing tendency to rotates - Rate of Rotation ( ) = In radians, determines the number of turns per unit time (rad/s) - If we look at the example of a spinning bicycle wheel, we find that (angular momentum – the tendency of the wheel to keep spinning) is proportional to the radius of the wheel (a), the mass of the wheel (m )wand the rate of rotation ( )  m w 2  a  - The properties inherent to the wheel are assembled as the moment of inertia (its inertia with respect to rotational motion) of the wheel: 2 2 I = m w a (mass x radius ) - The angular momentum of the spinning wheel is: L = I  - If we can determine I for a planet, we can learn something useful about how mass or density is distributed within • Perfectly spherical2planet of uniform density - I = (2/5)(ma ) • Perfectly spherical planet with mass concentrated in thin surface layer - I = (2/3)(ma )2 • Perfectly spherical planet with all mass concentrated at its centre - I = 0 - The lower the moment of inertia, the more concentrated the mass it at the centre. 2 - I < 0.4ma  mass concentrated towards centre - I = 0.4ma  uniform density - I > 0.4ma  mass concentrated towards surface - The lower the moment of inertia, the more mass is concentrated at the depth. 7.2 Determining I by Astronomic Observations - We can neither brake nor accelerate the rotation of a planet in order to measure its moment of inertia – this can be determined by observing a planet’s response to astronomical forces and torques. - Inertial space = background reference (frame of reference) provided by the phenomenon of inertia) - When a body rotates on an axle, it maintains its angular momentum vector fixed in inertial space • The axis of rotation (the centre around which the Earth spins) orbits the Sun in an ellipse. • The axis of rotation is fixed in inertial - Torque = The angular force that causes a change in rotation. • Torque is the force that is, at a distance, applied to the axis of rotation - When a torque is applied to the axle, a reactive torque exactly 90 to applied torque results in maintaining torque balances. - The Moon applies a twisting torque to the axle upon which the Earth rotates – the reaction torque causes the Earth’s axis to move in a direction 90 to the applied torque. - The Earth is a slightly flattened ellipsoid (it’s equatorial radius is greater than its polar radius) - The Moon’s present location is not aligned with the equator of the Earth. - On the side that is closer to the moon, there is a great
More Less

Related notes for CHEM 222

OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Join to view

OR

By registering, I agree to the Terms and Privacy Policies
Just a few more details

So we can recommend you notes for your school.