Chapter 4: Making Chapter 4: Making Sense of The Sense of The Universe: Matter, Universe: Matter, Energy & GravityEnergy & Gravity

What Is Matter?What Is Matter?

Matter is the Matter is the ““stuffstuff”” that makes up that makes up our our ““thingsthings””

Matter is composed of atoms and Matter is composed of atoms and their constituentstheir constituents

These These ““elementselements”” combine to form combine to form the molecules of lifethe molecules of life

Matter has MASS - Mass is an Matter has MASS - Mass is an intrinsic property of matterintrinsic property of matter

What Is Energy?What Is Energy?

Energy comes in different forms: Energy comes in different forms: - Kinetic (motion)- Kinetic (motion)- Potential (stored)- Potential (stored)- Radiative (electromagnetic)- Radiative (electromagnetic)

Mass can be turned into EnergyMass can be turned into Energy Energy can become MassEnergy can become Mass

E=mcE=mc22

Energy can change type but not be Energy can change type but not be created or destroyed.created or destroyed.

                                                                                                                         

                                                                     

Matter is composed of atoms

The Periodic ChartThe Periodic Chart

These elements all have unique chemical properties, based on the number of protons, neutrons and electrons they are composed of.

If you add or remove neutrons from the most common form of an element, you create Isotopes.

Stripping electrons from an atom is called Ionization.

Phases of MatterPhases of Matter

SolidSolid LiquidLiquid GasGas PlasmaPlasma

The state changes as you increase the temperature (add energy)

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Thermal Energy: Thermal Energy:

The collective kinetic energy of many particlesThe collective kinetic energy of many particles

(for example, in a rock, in air, in water)(for example, in a rock, in air, in water)– Thermal energy is related to temperature but it is NOT Thermal energy is related to temperature but it is NOT

the same.the same.– TemperatureTemperature is the is the averageaverage kinetic energy of the many kinetic energy of the many

particles in a substance.particles in a substance.

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Temperature ScalesTemperature Scales

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Temperature ScalesTemperature Scales

Thermal energy is a measure of the total kinetic Thermal energy is a measure of the total kinetic energy of all the particles in a substance. It therefore energy of all the particles in a substance. It therefore depends on both depends on both temperaturetemperature AND AND density.density. Example:Example:

Atoms & OrbitsAtoms & Orbits

Matter appears solid, but is composed Matter appears solid, but is composed of mostly empty space!of mostly empty space!

Electrons orbit atoms in clouds, with Electrons orbit atoms in clouds, with higher energy electrons in farther higher energy electrons in farther orbitsorbits

Atomic Energy StatesAtomic Energy States

Potential EnergyPotential Energy

Potential EnergyPotential Energy is the energy is the energy something has just because it has something has just because it has mass and is where it ismass and is where it is

Think of a boulder on a hill as an Think of a boulder on a hill as an example, when it rolls down it turns example, when it rolls down it turns potential energy into potential energy into Kinetic EnergyKinetic Energy(U=mgh)(U=mgh)

Simply by having mass that can be Simply by having mass that can be turned into energy is potential…turned into energy is potential…

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Gravitational Potential Gravitational Potential EnergyEnergy

In space, an object or In space, an object or gas cloud has more gas cloud has more gravitational energy gravitational energy when it is spread out when it is spread out than when it than when it contracts.contracts.– A contracting cloud A contracting cloud

converts gravitational converts gravitational potential energy to potential energy to thermal energy.thermal energy.

Kinetic EnergyKinetic Energy

When mass is moved it is When mass is moved it is Kinetic Kinetic EnergyEnergy (T=1/2 mv(T=1/2 mv22))

Adding energy to a system, i.e. as Adding energy to a system, i.e. as heat, will make the atoms more heat, will make the atoms more energetic and they will move energetic and they will move more, colliding with other atoms – more, colliding with other atoms – this is Kinetic Motionthis is Kinetic Motion

Temperature Temperature ~~ Energy Energy

Conservation of Conservation of EnergyEnergy In a closed system, the sum total of the energy is In a closed system, the sum total of the energy is

conservedconserved

The UniversalThe UniversalLaws of MotionLaws of Motion

MotionMotion

What is the difference between: What is the difference between: Speed, Velocity & Acceleration?Speed, Velocity & Acceleration?

Speed is a scalar, that means that it is Speed is a scalar, that means that it is how fast you go, but without specific how fast you go, but without specific directiondirection

Velocity is a vector, it gives speed and Velocity is a vector, it gives speed and directiondirection

Acceleration is found when an object is Acceleration is found when an object is speeding up or slowing downspeeding up or slowing down

FormulaeFormulae

v = v = ΔΔx/ x/ ΔΔtt

a = a = ΔΔv/ v/ ΔΔtt

g = 9.81 m/sg = 9.81 m/s22

Mass & MomentumMass & Momentum

Mass is an intrinsic property of matter. Mass is an intrinsic property of matter. The atomic mass is invariant, The atomic mass is invariant, regardless of your gravitational field regardless of your gravitational field (or speed)(or speed)

Weight is a Force, it changes Weight is a Force, it changes depending on your gravitational fielddepending on your gravitational field

Momentum is Momentum is mass x velocitymass x velocity, it tells , it tells you that big-fast things are harder to you that big-fast things are harder to stop than small-slow things.stop than small-slow things.

p = mvp = mv

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Sir Isaac Newton(1642–1727)

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

Realized the same physical Realized the same physical laws that operate on Earth laws that operate on Earth also operate in the also operate in the heavensheavens– oneone universe universe

Discovered laws of motion Discovered laws of motion and gravityand gravity

Much more: experiments Much more: experiments with light, first reflecting with light, first reflecting telescope, calculus…telescope, calculus…

NewtonNewton’’s Laws of Motions Laws of Motion

First Law: An object at rest remains at First Law: An object at rest remains at rest, and an object in motion remains rest, and an object in motion remains in motion, unless acted upon by an in motion, unless acted upon by an external forceexternal force

Second Law: F = ma = Second Law: F = ma = ΔΔp/ p/ ΔΔttForce depends on rate of change of Force depends on rate of change of momentum.momentum.

Third Law: For every force, there is an Third Law: For every force, there is an equal and opposite forceequal and opposite force

Conservation of Conservation of MomentumMomentum NewtonNewton’’s laws imply the concept of s laws imply the concept of

conservation of momentum. The total conservation of momentum. The total momentum in a system is conserved.momentum in a system is conserved.

Angular momentum acts on a body in Angular momentum acts on a body in orbit around another, held by the orbit around another, held by the gravitational force. In the absence of gravitational force. In the absence of net torque, the angular momentum net torque, the angular momentum remains constant.remains constant.

angular momentum = mvrangular momentum = mvr

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Angular momentum conservation also Angular momentum conservation also explains why objects rotate faster as explains why objects rotate faster as they shrink in radius.they shrink in radius.

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Center of MassCenter of Mass

Because of Because of momentum momentum conservation, orbiting conservation, orbiting objects orbit around objects orbit around their center of mass.their center of mass.

NewtonNewton’’s Universal Law of s Universal Law of GravitationGravitation

Every mass attracts other mass through the Every mass attracts other mass through the force called gravityforce called gravity

The force of attraction between any two The force of attraction between any two objects is directly proportional to the product objects is directly proportional to the product of their massesof their masses

The force of attraction between two objects The force of attraction between two objects decreases with the square of the distance decreases with the square of the distance between their centersbetween their centers

FFgg = GM = GM11MM22/d/d22

(note that G is the gravitational constant)(note that G is the gravitational constant)

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What determines the What determines the strength of gravity? strength of gravity?

The The universal law of gravitation:universal law of gravitation:

1.1. Every mass attracts every other mass.Every mass attracts every other mass.

2.2. Attraction is Attraction is directlydirectly proportional to the product of proportional to the product of their masses.their masses.

3.3. Attraction is Attraction is inverselyinversely proportional to the proportional to the squaresquare of of the distance between their centers.the distance between their centers.

NewtonNewton’’s Influences Influence

Some 70 years after Kepler published his Some 70 years after Kepler published his three laws of orbital motion, Newton was three laws of orbital motion, Newton was able to explain able to explain ““whywhy”” they held true! they held true!

Science strives to observe, determine Science strives to observe, determine relationships and eventually discover relationships and eventually discover ““whywhy”” things work the way they do.things work the way they do.

NewtonNewton’’s laws remained unchallenged until s laws remained unchallenged until an upstart named Albert Einstein developed an upstart named Albert Einstein developed a general theory of gravity that was more a general theory of gravity that was more precise in 1905.precise in 1905.

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How does Newton's law of gravity How does Newton's law of gravity extend Kepler's laws?extend Kepler's laws?

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

Ellipses are not the Ellipses are not the only orbital paths. only orbital paths. Orbits can be:Orbits can be:– bound (ellipses)bound (ellipses)– unboundunbound

parabolaparabola hyperbolahyperbola

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How do gravity and energy How do gravity and energy together allow us to together allow us to understand orbits?understand orbits?

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

Orbits cannot Orbits cannot change change spontaneously.spontaneously.

Total orbital energy stays constant.

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How does gravity cause How does gravity cause tides?tides?

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

Difference in Moon's gravitational pull stretches Earth.Difference in Moon's gravitational pull stretches Earth.

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Tidal friction gradually slows Earth's rotation (and makes the Tidal friction gradually slows Earth's rotation (and makes the Moon get farther from Earth).Moon get farther from Earth).

The Moon once orbited faster (or slower); tidal friction caused The Moon once orbited faster (or slower); tidal friction caused it to ''lock'' in synchronous rotation. it to ''lock'' in synchronous rotation.

Tidal FrictionTidal Friction

Gravity Rules!Gravity Rules!

The gravitational influence of the Moon cause The gravitational influence of the Moon cause the tidesthe tides

Leaving the surface of Earth takes a lot of Leaving the surface of Earth takes a lot of energy, it is like crawling out of a deep well. energy, it is like crawling out of a deep well. The escape velocity is about 40,000 km/hr.The escape velocity is about 40,000 km/hr.

While the other fundamental forces While the other fundamental forces (electromagnetic, strong and weak) are much (electromagnetic, strong and weak) are much stronger, their range is short and the motion stronger, their range is short and the motion of the stars and galaxies are bound by of the stars and galaxies are bound by gravity.gravity.

Free FallFree Fall

Why are astronauts weightless in Why are astronauts weightless in space?space?

They are in a constant state of They are in a constant state of free fall.free fall.

The Force from gravity in the The Force from gravity in the space station from Earth is not space station from Earth is not much less than on the surface!much less than on the surface!