How to Study the Universe

Question:

How are we going to be able to “understand”

what we see in the universe

if all we have to work with

is the LIGHT that we see?

Answer:

We will apply some basic “knowledge” that we already know about the universe (on earth) to what we see beyond the earth.

Using this “basic knowledge” we can examine what we see and create an explanation or hypothesis that we can test.

We then use the SCIENTIFIC METHOD to test our hypothesis.

This allows us to understand and explain what we observe.

ALL of THIS CAN BE ACCOMPLISHED FROM A DISTANCE.

We will use our “Problem Solving Techniques.” ******************************************************** We will begin our examination by asking “What is given”.

We can say 1. We have a good knowledge of things on our earth.

2. We understand the concepts of   mass motion force energy electromagnetic radiation (to be examined later)

We will apply our knowledge ofthese concepts

beyond the earth

to attempt to understand

what we observe in the universe.

Next we must ask “What is asked for”?  1. What do we see when we observe the universe?

2. The answer is we observe some of the same things we see on our earth.

3. We observe some of the following:

- mass moving (orbiting planets, moons)

- light patterns (red shifts, Doppler movements) 4. So, to understand these observations in space

- we need to understand how these “observations” occur on our earth.

Having identified the things we are looking for we can ask

“What type of problem is this”?

Just like we do on earth. Therefore we must examine the relationships between mass motion force energy electromagnetic radiation (later) So we begin our journey with a review of these concepts.

MASS Mass = the amount of matter in an object

MOTION

Motion = a mass moving  Two types of movement  - linear (straight line)

- angular (non-linear can be -- a circle or an ellipse)

VELOCITY

Velocity = (the speed) + (direction) of the motion of mass.

Expressed as a VECTOR QUANTITY

MAGNITUDE expressed as distance/time (10km/hr)

DIRECTION expressed in a direction (west) 

30 km/hr

west

How do we describe motion?

Precise definitions to describe motion:

• Speed: Rate at which object moves

speed = distancetime

units of ms

Example: speed of 10 m/s

• Velocity: Speed and direction Example: 10 m/s, due east

• Acceleration: Any change in velocity; units of speed/time (m/s2)

Acceleration

•Acceleration: Any change in velocity; units of speed/time (m/s2)

Magnitude increases

Direction changes

Magnitude decreases

Force

Is defined as

anything that can cause

a change in the momentum of an object

We observe it as a change in the

motion of an object

PUSH

PULL

Because there are two types of motion (linear and non-linear)

we have two types of momentum  Linear Momentum = (mass) x (velocity)  Angular momentum = (mass) x (velocity) x (radius of circle)

Momentum

What type of motion do we observe? We can observe a mass to do three things:  1. remain at rest (no motion)

2. move at a constant velocity

-- in a straight line (linear motion) -- in circular direction (angular motion)

3. accelerate, this can be can be a change in -- speed -- direction -- both

What type of motion do we observe?

If we can understand the relationship between

these types of motion and

the concepts of mass, force and energy

we can explain the motion we observe.  It doesn’t matter of the motion is on earth or space.

Earth

Space

Fortunately,

Isaac Newton put all of this together

in his famous

three laws of motion.

He realized the same physical laws that operate on Earth

also operate in the heavens: one universe

He discovered laws of

motion and

gravity.

Much more: Experiments with

light

first reflecting telescope,

calculus… Sir Isaac Newton

(1642–1727)

How did Newton change our view of the universe?

An object moves at

constant velocity

unless a net force acts

to change its speed and/or

or direction.

Newton’s first law of motion

If a body is at rest it will remain at rest.

If a body is in motion it will remain in motion.

Force = mass acceleration.

F = ma

Newton’s second law of motion

For every force,

there is always an equal

and opposite

reaction force.

Newton’s third law of motion

We have now seen the mass in motion,

but what causes the mass to move?

The answer is

ENERGYEnergy is what makes matter move

Basic Types of Energy

• Kinetic (motion)

• Radiative (light)

• Stored or potential

Energy can change type but cannot be destroyed.

Thermal Energy: The collective kinetic energy of many particles

(for example, in a rock, in air, in water)

Thermal energy is related to temperature

but it is NOT the same.

Temperature is the average kinetic energy

of the many particles in a substance.

Temperature Scales

Astronomy uses the Kelvin scale.

Gravitational Potential Energy on Earth

On Earth,

it depends on…

an object’s mass (m).

the strength of gravity (g).

the distance an object

could potentially fall.

Gravitational Potential Energy in Space

In space,

an object or gas cloud

has more gravitational energy

when it is spread out than

when it contracts.

A contracting cloud

converts gravitational potential energy

to thermal energy.

We will examine this more closely when we look at the formation of the solar system and stellar evolution.

Let us review, we have observed   - mass moving  - mass having momentum  - the presence of a force

- causes motion

- which tells us that

- energy is involved

Mass itself is a form of potential energy.

E = mc2

A small amount of mass

can release a

great deal of energy.

The conservation of total energy  

The conservation of total momentum 

Now we must introduce two more very important concepts

Conservation of Energy

• Energy can be neither created nor destroyed.

• It can change form or be exchanged between objects.

• The total energy content of the universe

• was determined in the Big Bang and remains the same today.

Conservation of Momentum

The total momentum of interacting objects

cannot change

unless an external force is acting on them.

Interacting objects exchange momentum

through equal and opposite forces.

What keeps a planet rotating and orbiting the Sun?

Conservation of Angular Momentum

The angular momentum of an object

cannot change unless an

external twisting force (torque)

is acting on it.

Earth experiences

no twisting force as it orbits the Sun,

so its rotation and orbit

will continue indefinitely.

angular momentum = mass velocity radius

Angular momentum conservation

also explains why objects

rotate faster as they shrink in radius.

Gravity is

a force of attraction

that exists

between any two masses,

any two bodies,

any two particles.

What is Gravity?

Gravity is not just the attraction between objects and the Earth.

It is an attraction that exists between all objects,

everywhere in the universe.

Sir Isaac Newton (1642 -- 1727) discovered that a force is required to change the speed or direction of movement of an object.

He also realized that the force called "gravity“

must make an apple fall from a tree,

or humans and animals live on the surface of our spinning planet without being flung off.

Furthermore, he deduced that gravity forces exist between all objects.

The Universal Of Gravitation

What determines the strength of gravity?

The Universal 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.

Important things we have learned.

Objects in the universe have mass.

The motion of body is described by Newton's three laws.

A force is required to cause motion or a change in motion.

Energy is what causes the force.

All mass (matter) is attracted to other matter.

This force of attraction is called GRAVITY.

GRAVITY exists between all mass (matter) in the universe.

Therefore

If we can observe and

understand it on earth

we can observe and

understand it in space.

The End