Chapter 3: The laws of motion Flashcards
Explain the geocentric model by Ptolemy. What were some problems with it?
- Earth-centered model
- the sun, the moon, and the planets visible to naked eye (Mercury, Venus, mars, Jupiter, saturn) all moved in circles around a stationary Earth
- problems: Moons of Jupiter, Imperfections of Moon and Sun, Each planet treated differently, Phases of Venus
How did Copernicus revolutionize astronomy? What is this model called? What happens in this model?
- by placing Sun at center of model
- heliocentric model
- the outer planets (Mars, Jupiter, Saturn) undergo apparent retrograde motion when Earth overtakes them in their orbits
- inner planets (Mercury and Venus) move in apparent retrograde motion when overtaking Earth
What is apparent retrograde motion?
planets would seem to turn around, move westward for a while, and then return to their normal eastward travel
What is a frame of reference?
a system within which an observer measures positions and motions using coordinates such as distance and time
All solar system objects exhibit apparent retrograde motion except for ?
sun
What is Kepler’s 1st Law of planetary motion?
- Planetary orbits are ellipses, each ellipse has two foci.
-The Sun is at one focus of a planet’s elliptical orbit.
-Ellipse described by:
Semi-major axis: typically measured in AU; half of the longest length
Eccentricity: number ranging from 0 to 1; describes how elongated the ellipse is
What is Kepler’s 2nd law of planetary motion?
- the Law of Equal Areas
- The line between the Sun and the planet “sweeps” out equal areas in equal times.
- Planet travels fastest when it is closest to the Sun and slowest when it is farthest from the sun
What is Kepler’s 3rd law of planetary motion?
- distant objects travel at lower speeds
- period (years it takes to get around a planet’s orbit) squared is equal to the semimajor axis of the planets orbit (average distance from the sun) (AU) cubed (p^2 = a^3)
What do Newton’s laws generally explain?
- why objects in the universe move the way they do.
- how planets (and comets, asteroids, dwarf planet, etc.) orbit the Sun according to Kepler’s observationally-derived Laws.
What is Newton’s 1st law of motion?
-describes inertia, An object at rest will remain at rest and an object in motion will continue moving along a straight line with a constant speed until an unbalanced force acts on it.
What is Newton’s 2nd law of motion?
If a net force (an unbalanced force) acts on an object, then the object’s motion changes (causes acceleration).
-acceleration = force/mass
What is Newton’s 3rd law of motion?
forces always occur in action-reaction pairs.
Acceleration (a) =
- force (f) / mass (m)
- the rate at which the velocity of an object changes
Velocity =
speed + direction
What is the gravitational force?
the mutually attractive force between two objects with mass
All objects on Earth have been experimentally shown to fall with the same gravitational acceleration (g), what is it?
g = 9.8 m/s^2.
Weight is the product of your mass and the acceleration due to gravity. What is the equation?
𝐹(𝑤𝑒𝑖𝑔ℎ𝑡)=𝑚𝑔
Define Newton’s universal law of gravitation. What does it depend on? Equation:
-Gravity is an attractive, mutual force between any two objects with mass.
-It depends on: Mass of first object, Mass of second object, Distance between objects
F (force) = G (constant) m1m2 (masses) / r2 (distance)
What is the inverse square law?
At a particular Luminosity, the more distant an object is, the fainter its apparent brightness becomes as the square of the distance
What is the universal gravitational constant?
Determines the strength of gravity between objects, and it is the same for all pairs of objects
G = 6.673 x 10^-11 m^3/(kg s^2)
What is centripetal force?
a force toward the centre of a circle (Gravity provides the centripetal force that holds a satellite in its orbit)
