Chapter 4 Astonomy

4.1 Describing Motion 4.2 Newton's Laws of Motion 4.3 Conrvation Laws in Astronomy 4.4 The Universal Law of Gravitation 4.5 Orbits, Tides and the Acceler of Gravity

Speed

Rate at which object moves

Veolcity

Speed and direction

Acceleration

Any change in velocity, units of speed/time (m/s2)

According to the theory of the acceleration of gravity, All falling objects accelerate at ____ rate (not counting friction of air resistance

the same

Momentum =

mass x velocity

Net force

changes momentum, which
generally means an acceleration (change in
velocity)

Angular momentum

Rotational momentum of a spinning or orbiting
object

mass

the amount of matter in an object

weight

the force that acts upon an object

True or False

There is NO gravity in space

False

What is weightlessness due to in space?

a constant state of
free-fall

Who realized the same
physical laws that operate
on Earth also operate in
the heavens
– one universe

newton

Who discovered laws of motion
and gravity

Newton

what is newtons first law of motion

An object
moves at constant
velocity unless a net
force acts to change its
speed or direction.

What is Newtons second law of motion

Force = mass x acceleration

• or Force = rate of change in momentum

What is Newtons third law of motion?

For every force, there is always an equal and
opposite reaction force.

What did Newton discover laws of?

Motion and Gravitation

Objects continue at constant velocity
because of

conservation of momentum

True or False

The total momentum of interacting objects cannot change unless an external force is acting on them

True

What do interactinf objects exchange through equal and opposite forces?

momentum

Angular momentum =

mass x velocity x radius

What is torque

an external twisting force

The angular momentum of an object cannot
change unless a(n)
is acting on it.

torque

What keeps a planet (Earth) rotating and orbiting the sun

Earth experiences no twisting force as it orbits
the Sun, so its rotation and orbit will continue
indefinitely.

Why do objects rotate faster as the shrink in radius?

Angular momentum conservation

Energy makes matter _____

move

What can transfer from one object to another and change in form?

Energy

Basic Types of Energy

Kinetic, Radiative, Potential

True or False

Energy can change type,
but cannot be created or
destroyed.

True

Kinetic Energy is

motion

Radiative energy is

light

Potential energy is

stored

Thermal energy is what kind of energy?

the collective kinetic energy of many particles

What energy is related to temperature but
it is NOT the same

Thermal

Temperature is

the average kinetic energy of
the many particles in a substance.

What does thermal energy depend on?

temperature AND
amount of matter

Gravitational Potential energy on Earth depends on:

• object's mass (m)

• strength of gravity (g)

• distance object could
  potentially fall

In space, an object or
gas cloud has ______
gravitational energy
when it is spread out
than when it
contracts.

more

What does a contracting cloud convert gravitational
potential energy into

thermal energy

Mass is a form of _____ energy

potential

True or False

Concentrated energy cannot
spontaneously turn into particles
(for example, in particle
accelerators)

Why do objects move at constant velocity if no force
acts on them?

Conservation of momentum

What keeps a planet rotating and orbiting the Sun?

Conservation of angular momentum

Where do objects get their energy?

energy cannot be created or
destroyed but only transformed from one type to
another

What is the law of gravitation?

1. Every mass attracts every other mass.

2. Attraction is directly proportional to the product of their masses.

3. Attraction is inversely proportional to the square of the distance between their centers.

True or False

Kepler's laws apply to all
orbiting objects, not just
planets

True

Ellipses are not the only
orbital paths. Orbits can
be:

bound (ellipses) and unbound

Parabola and hyperbola ellipses are examples of bound or unbound?

Unbound

Because of ____ orbiting objects orbit around their ceneter of mass

momentum conservation

what tells us the total mass of a system according to newtons laws of gravity?

the laws of gravity and motion showed the
relationship between the orbital period and average
orbital distance of a system

what does Earth's orbital period (1 year) and average distance
(1 AU) tell us

the Suns mass

what does Orbital period and distance of a satellite from Earth
tell us

Earths mass

what does Orbital period and distance of a moon of Jupiter tell
us

Jupiters mass

What determines the strength of gravity?

Directly proportional to the product of the
masses (M x m)
– Inversely proportional to the square of the
separation

How does Newtons laws of gravity allow us to
extend Kepler's laws

• Applies to other objects, not just planets

• Includes unbound orbit shapes: parabola,
  hyperbola

• Can be used to measure mass of orbiting
  systems

Why can orbits not change spontaneously?

Total orbital energy (gravitational + kinetic) stays constant if there is no external force.

True or False

Total orbital energy stays constant

True

what can make an
object gain or lose orbital
energy?

Friction or atmospheric
drag - a gravitational encounter

If an object gains
enough ________,
it may escape (change
from a bound to
unbound orbit).

orbital energy

What is the escape velocity from Earth in km/s from sea level

11

How does gravity cause tides?

Moon's gravity pulls harder on near side of Earth
than on far side

What cause the Earth to stretch in reference to the moon?

the difference in Moon's gravitational pull

What does tidal friction do to Earth?

Slows its rotation

What does tidal friction do to the moon

causes it to become farther from the earth

What caused the moon to “lock” in synchronus rotation?

The moon once orbited faster (or slower) and, causing todal friction

Why do all objects fall at the same rate?

The gravitational acceleration of an object
does not depend on its mass because the object in the
equation for acceleration cancels the object in the equation
for gravitational force

What was not understood until Einsteins general theory of relativity?

Mass of object in Newtons second law exactly cancels mass of law of gravitation

Why would a cannon ball orbit Earth?

because the speed of the cannon ball is great enough to put the cannon ball into free-fall

Space Station astronauts are weightless because

their acceleration is equal to the acceleration due to gravity

If you take off in a rocket accelerating upward

your mass stays the same and your weight increases

All of Newtons laws of motion express the concept that

a force (and only a force) always changes the momentum of an object

When a ball is dropped, some of the balls energy changes from

gravitational potential energy to kinetic energy

When two objects collide their combined momentum remains unchange (T/F)

True

When two objects collide they exert _____ and _____ forces oon each other

equal, opposite

when two objects collide their combined angular momentum is

unchanged

when two objects collide their combined energy is

unchanged

The acceleration due to gravity of an object on the surface of Earth depends on

the radius and mass of earth

What happens to the energy of an object while it follows an unbound orbit around the Sun?

The total remains constant while gravitational potential energy is converted to kinetic energy as it approaches the Sun

What are the phases of the Moon that occur when neap tides occur?

first quarter, third quarter

During which phases of the Moon do extremely high tides occur?

Full

How many hightides occur on Earth each day?

two