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**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?

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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.

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**We will use our “Problem Solving Techniques.”**

******************************************************** We will begin our examination by asking “What is given”. We can say We have a good knowledge of things on our earth. We understand the concepts of mass motion force energy electromagnetic radiation (to be examined later)

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**We will apply our knowledge of**

these concepts beyond the earth to attempt to understand what we observe in the universe.

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**Next we must ask “What is asked for”?**

What do we see when we observe the universe? The answer is we observe some of the same things we see on our earth. 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.

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**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.

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MASS Mass = the amount of matter in an object

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MOTION Motion = a mass moving Two types of movement - linear (straight line) - angular (non-linear can be -- a circle or an ellipse)

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**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

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**How do we describe motion?**

Precise definitions to describe motion: Speed: Rate at which object moves 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) Basic vocabulary of motion. Emphasize that turning, slowing, and speeding up are all examples of acceleration.

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**Acceleration Magnitude increases Direction changes Magnitude decreases**

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

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**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

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**Momentum 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)

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**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

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Space 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

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Fortunately, Isaac Newton put all of this together in his famous three laws of motion.

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**How did Newton change our view of the universe?**

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)

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**An object moves at Newton’s first law of motion constant velocity**

unless a net force acts to change its speed and/or or direction. You may wish to discuss the examples in the book on P. 83–84. If a body is at rest it will remain at rest. If a body is in motion it will remain in motion.

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**Newton’s second law of motion**

Force = mass acceleration. F = ma

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**Newton’s third law of motion**

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

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**ENERGY We have now seen the mass in motion,**

but what causes the mass to move? The answer is ENERGY Energy is what makes matter move

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**Basic Types of Energy Kinetic (motion) Radiative (light)**

Stored or potential Energy can change type but cannot be destroyed.

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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. Students sometimes get confused when we’ve said there are three basic types of energy (kinetic, potential, radiative) and then start talking about subtypes, so be sure they understand that we are now dealing with subcategories.

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**Temperature Scales Astronomy uses the Kelvin scale.**

Use this figure to review temperature scales. Astronomy uses the Kelvin scale.

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**Gravitational Potential Energy on Earth**

it depends on… an object’s mass (m). the strength of gravity (g). the distance an object could potentially fall. We next discuss two subcategories of potential energy that are important in astronomy: gravitational potential energy (this and next slide) and mass-energy.

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**Gravitational Potential Energy 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 next discuss two subcategories of potential energy that are important in astronomy: gravitational potential energy and mass-energy. We will examine this more closely when we look at the formation of the solar system and stellar evolution.

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**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

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**E = mc2 Mass itself is a form of potential energy.**

A small amount of mass can release a great deal of energy.

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**Now we must introduce two more very important concepts **

The conservation of total energy The conservation of total momentum

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**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. You might wish to go through the example tracing the energy of a baseball back through time, as described on p. 90 of the text.

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**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. You may wish to discuss the examples given in the text on p. 79.

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**What keeps a planet rotating and orbiting the Sun?**

You may wish to go over this figure in some detail to be sure the idea is clear.

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**Conservation of Angular Momentum**

angular momentum = mass velocity radius 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. You may wish to discuss the examples given in the text on p. 79.

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**Angular momentum conservation also explains why objects **

rotate faster as they shrink in radius. Discuss astronomical analogs: disks of galaxies, disks in which planets form, accretion disks…

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**What is Gravity? Gravity is a force of attraction that exists**

between any two masses, any two bodies, any two particles.

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

It is an attraction that exists between all objects, everywhere in the universe.

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Sir Isaac Newton ( ) 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.

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**The Universal Of Gravitation**

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**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.

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**Therefore If we can observe and understand it on earth**

understand it in space.

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The End

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