Week 3
If an object moves along a circular path at a constant speed, you can infer that
A force is acting on it and it is accelerating.
Which of the following objects (1-4) are accelerating?
An object in motion in a straight line with increasing speed An object moving in a circle at constant speed
The Earth's escape speed (the speed you need to get away forever) is about 25,000 miles per hour. Escape speed depends on the gravity of the object trying to hold the spacecraft from escaping. Based on your understanding of gravity, how will the escape speed from the Moon compare to the escape speed from Earth?
The Moon's escape speed will be smaller than Earth's
Kepler's third law
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Which of the following does not provide evidence of a spherical Earth?
These are all evidence of a spherical Earth.
Why are astronauts in the International Space Station described as being weightless?
They are constantly falling toward Earth.
How are mass and weight different?
Weight is a measure of how much gravity pulls an object; mass is how much matter the object has.
Based on the scientific and statistical tests of astrological predictions, which of the following statements is the most reasonable?
astrology has not passed any clear scientific or statistical test and, as a result, most scientists are very doubtful that it can predict anything meaningful about our lives
The gravitational force exerted by the Sun on Earth is _________ the gravitational force exerted by Earth on the Sun.
equal to
To leave the gravitational pull of the Earth, and explore other planets, satellites must have at least
escape velocity
According to Kepler's 2nd Law, comets (which have eccentric orbits) should spend a lot more of their time
far from the Sun
The acceleration experienced by Earth is ________ the acceleration experienced by the Sun.
greater than
If an object's mass (M) is doubled, the gravitational force between it and other objects will be
increased by a factor of 2.
The heliocentric model of Copernicus won favor among astronomers primarily because
it explained retrograde motion more simply than the earlier geocentric model.
To figure out what you weigh on the surface of the Moon (how much gravity there pulls you downward), you need to know
just the mass of the Moon. just the distance from the Moon's center to its surface
When a planet, in its orbit, is closer to the Sun, it A. moves slower than average
moves faster than average
The slow tipping of the Earth's axis in a circle with a period of about 26,000 years is called
precession
When a planet temporarily moves westward in the sky over the course of several weeks or months (instead of eastward, as it typically does), we call it
retrograde motion
Newton's reformulation of Kepler's third law allows us to measure the masses of bodies in orbit around each other, if we can measure
the distances and periods of revolution
What problem has precession caused for many of the schools of astrology?
Because of precession, the constellations are no longer lined up with the astrological signs that are named after them; since astrology was set up, the two have slipped one sign apart
What is the equation for Newton's Law of Gravity?
F = G m1 m2/r2
Which of the following is a contribution that Eratosthenes made to astronomy?
He determined the circumference of the Earth.
Black holes are objects with an escape velocity faster than the speed of light. If the Sun were to magically turn into a black hole with a mass equal to the Sun's mass, what would happen to the orbits of the planets?
Nothing, but it would get really dark.
If the distance between two masses is tripled, the gravitational force between them is
decreased by a factor of 9
