Astronomy Chapter 4 Reading and Concept

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Cooney, The Essential Cosmic Perspective, 6th Edition

The difference between speed and velocity is that _________.

velocity also includes a direction

The acceleration of gravity on Earth is approximately 10 m/s2 (more precisely, 9.8 m/s2). If you drop a rock from a tall building, about how fast will it be falling after 3 seconds?

30 m/s

Momentum is defined as _________.

mass times velocity

What happens to your weight and your mass on the moon?

Your weight would be less than your weight on Earth, but your mass would be the same as it is on Earth.

In which of the following cases would you feel weightless?

While falling from a roof

"What goes up must come down" is True or False according to Newtons Laws of Motion?

False- This is not one of Newton's laws, and it's not even true: Objects with escape velocity can go up without coming back down.

Newton's Second Law of Motion tells us that the net force applied to an object equals its _________.

mass times acceleration

Suppose that two objects collide. What is not the same both before and after the collision?

The total temperature of the objects

When a spinning ice skater pulls in his arms, he spins faster because _________.

his angular momentum must be conserved, so reducing his radius must increase his speed of rotation

The energy attributed to an object by virtue of its motion is known as _________.

kinetic energy

Radiative energy is _________.

energy carried by light

Absolute zero is _______.

0 Kelvin

What does temperature measure?

The average kinetic energy of particles in a substance

In the formula E=mc2, what does E represent?

The mass-energy, or potential energy stored in an object's mass

According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them _________.

decreases by a factor of 9

What is the difference between a bound orbit and an unbound orbit around the Sun?

An object on a bound orbit follows the same path around the Sun over and over, while an object on an unbound orbit approaches the Sun just once and then never returns.

What do we mean by the orbital energy of an orbiting object (such as a planet, moon, or satellite)?

Orbital energy is the sum of the object's kinetic energy and its gravitational potential energy as it moves through its orbit.

Which statement must be true in order for a rocket to travel from Earth to another planet?

It must attain escape velocity from Earth.

Why is Newton's version of Kepler's third law so useful to astronomers?

It can be used to determine the masses of many distant objects.

Approximately where is it currently high tide on Earth?

On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon

What is an example of you not accelerating?

Driving in a straight line at 60 miles per hour

Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen?

Both will hit the ground at the same time.

Why are astronauts weightless in the Space Station?

Because the Space Station is constantly in free-fall around the Earth

A net force acting on an object will always cause a change in the object's _________.

momentum - Force is actually defined as the rate of change in momentum.

Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?

It is the same.

The planets never travel in a straight line as they orbit the Sun. According to Newton's second law of motion, this must mean that _________.

a force is acting on the planets - Because the planets are not traveling in straight lines, the planets are always accelerating, and Newton's second law tells us that a force must be acting to cause the acceleration.

Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen?

The Sun would rotate faster than it does now.

Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?

The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.

Suppose you heat an oven to 400°F and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?

The water can transfer heat to your arm more quickly than the air.

What is an example that involves energy that we would typically calculate with Einstein's formula E=mc2?

A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.

A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy?

The energy goes to producing sound and to heating the ground, rock, and surrounding air.

Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth?

Earth's orbit would be unaffected - The force of gravity between Earth and the Sun, and hence the orbital distance and speed of Earth, depends only on the Sun's mass (and the Earth-Sun distance), not on the Sun's size.

Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2MEarth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet?

1 year

Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year?

The planet's year would be shorter than Earth's.

Newton showed that Kepler's laws are _________.

natural consequences of the law of universal gravitation

Which pair of facts can be used with Newton's version of Kepler's third law to determine the mass of the Sun?

Earth is 150 million km from the Sun and orbits the Sun in one year.

When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened?

Saturn must have lost a very tiny bit of its orbital energy.

Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter's atmosphere and far from all of Jupiter's moons.) Which of the following statements would be true?

The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.

Which of the following best describes the origin of ocean tides on Earth?

Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.

At which lunar phase(s) are tides most pronounced (for example, the highest high tides)?

Both new and full moons

Which of the following best explains why the Moon's orbital period and rotation period are the same?

The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period.

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