ISNS 3371 - Phenomena of Nature Determining Planet Mass and Orbit Animation

ISNS 3371 - Phenomena of Nature

Determining Planet Mass and Orbit Animation


Remember - Doppler shift only tells us radial motion. If plane of orbit perpendicular to our line of sight - no shift seen. If we view it from edge on, maximum Doppler shift seen. Orbit generally tilted at some angle - star’s full speed not measured. So mass derived from Doppler technique is minimum possible. If varying position in sky measured (as in one case) orbital tilt can be determined and mass measured accurately.


• The Doppler technique yields only planet masses and orbits.

• Planet must eclipse or transit the star in order to measure its radius.

• Size of the planet is estimated from the amount of starlight it blocks.

• We must view along the plane of the planet’s orbit for a transit to occur.– transits are relatively rare

• They allow us to calculate the density of the planet.– extrasolar planets we have detected have Jovian-like densities.

Planetary Transit

Planetary Transit Animation


Orbital distances and approximate masses of first 77 planets discovered


Electricity and Magnetism

ISNS 3371 - Phenomena of Nature ChargeCharge - basic property of some elementary particles:

The electron has a negative charge (-1.6 X 10-19 C)

The proton has a positive charge of (+1.6 X 10-19 C)

The atom has an equal number of protons and electrons - it has no net charge.

Like charges repel one another and unlike charges attract one another.

The force between two charged particles is inversely proportional to the square of the distance between them and is called the Coulomb force:

(Coulomb’s Law)

k is a constant similar to G in Newton’s Law of Gravity (= 9 X 109 N m2/C2)

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F =kq1q2

d2


Electrostatic Charge

The buildup of electric charge on the surface of an insulated body

Examples: electroscope, balloon rubbed on hair, glass rod rubbed by fur, on body by rubbing feet on carpet

Can damage sensitive electronics - why technicians wear clothing made of special fabrics and wear grounding straps.

Can cause discharges on spacecraft - can cause damage or even failures

Can cause gasoline explosions - why plane is always grounded to fuel pump before refueling

Partially responsible for process of bacteria sticking to surfaces or other cells


Electrostatic charging on spacesuits while ISS travels through the aurora potentially hazardous situation

Safety Tether

Display and Control Module (DCM)

Body Restraint Tether (BRT)

Mini Work Station (MWS)

Surface of spacesuit could charge to high voltage leading to subsequent discharge.

Discharge to the station through safety tether:•Tether is a metallic cable - connected to astronaut via non-conducting (nylon) housing.• Station maintained at plasma potential - arc path closed when tether gets wrapped around astronaut.

Metal waist and neck rings and other metal portions of the suit make contact with the sweat soaked ventilation garment providing possible conducting path for discharge through astronaut’s thoracic cavity.


Voltage

Electric potential - change in electric potential is work done on charge by an electric (Coulomb) force.

Remember: work = force X distance (over which force is applied)

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Voltage =Electric Potential

Charge

Analogous to gravitational potential energy: work done by the force of gravity in moving a mass through a certain distance

Units of voltage are Volts (Joules/Coulomb). In a nine volt battery the potential difference between the positive and negative terminals is precisely nine volts.


Current

Establish a potential difference between two points and release some charges - charges will be acted on by the electrical force and start to move - this is a electric current - a flow of electrical charges. Just like the flow of H2O is a water current.

A current is the amount of charge that flows by a given point in a certain time interval. Unit is Ampere (A = Coulombs/second)

In electrical circuits, consist of electrons in the wire moving from lower to higher electrical potential.

By convention, electrical current flows from positive to negative - electrons flow in opposite direction. In other words, a positive current flows from higher to lower electrical potential.

ISNS 3371 - Phenomena of NatureResistivity and Circuits

If a wire is connected between two poles of a battery, a current flows. This is a circuit. The electrons do not move completely freely - there is a resistance to their flow - has to do with number of collisions electrons make with other electrons and atoms. Amount of current dependent of resistivity. Unit of electrical resistance is Ohm ().

Insulator - high resistivityConductor - low resitivitySuperconductor - zero resistivity

Dependent on material, temperature, length of wire

Electrical circuit like hydraulic circuit with flow of water analagous to flow of electrons.

ISNS 3371 - Phenomena of Nature PowerPower is the rate of energy flow. Unit is Watt ( Watt = Joules/second)

Power = Voltage X Current - 1 W = 1 VA

Total amount of energy used = Watt X Time, This is how the power company charges us for electricity - by the kilowatt hour (kWh)

The power rating of an appliance tells us the rate at which it uses electrical energy. For example, a 1500 watt hair dryer uses 1500 joules of electrical energy per second.

Keep a 60 watt light bulb on for a full day:

uses 60 watts x 24 hours = 1440 watt hours = 1.44 kilowatt hours of energy. At 9 cents per kilowatt hour this would cost just under 15 cents.

kilowatt hour is a unit of energy - can convert it to joules:

1.44 kWh = 1440 J/s X 3600 s = 5,184,000 J


QUANTITY SYMBOL UNIT MEANING

Charge Q Coulomb (C)

A basic property of some elementary particles. The electron has a charge of -1.6 X 10-19 C

and the proton has a charge of +1.6 X 10-19 C

Current I Ampere

(A)

(1 A = 1 C/sec)

Rate of flow of charge.

Potential Difference (voltage)

V Volt (V)

(1 V = 1 J/C)

J= Joule

Potential energy difference per coulomb of charge between two points; corresponds to pressure in water flow.

Electrical Quantities


QUANTITY SYMBOL UNIT MEANING

Resistance R Ohm (Ω)

1Ω =

1 V/A

A measure of the opposition to the flow of charge in a particular circuit. For a given voltage, the higher the resistance, the lower the current.

Power P Watt (W)

(1 W =

1 VxA)

Rate of energy flow.


Ohm’s Law states that the amount of current in a circuit is proportional to the voltage across the circuit and inversely proportional to the resistance in that circuit

I=V/R

or

V = IR

Voltage = Current x Resistance

Ohm’s Law

ISNS 3371 - Phenomena of NatureElectrical Shock

“It’s not the voltage but the current.”

The current is what actually causes a shock - human body has resistance of ~500,000 with dry skin - ~100 wet! Requires conducting path.

Can cause: (1) burning of tissue by heating, (2) muscle contractions, (3) disruption of cardiac rhythms.

Current (A) Effect

0.001 Can be felt

0.005 Is painful

0.010 Causes spasms

0.015 Causes loss of muscle control

0.070 Goes through the heart - fatal after more than 1 second


Circuits in Series

•Resistance (light bulbs) on same path•Current has one pathway - same in every part of the circuit•Total resistance is sum of individual resistances along path•Current in circuit equal to voltage supplied divided by total resistance•Sum of voltages across each lamp equal to total voltage•One bulb burns out - circuit broken - other lamps will not light (think of

string of old Christmas lights)

ISNS 3371 - Phenomena of NatureWater Analogy for Series Circuits

ISNS 3371 - Phenomena of Nature Parallel Circuits

•Bulbs connected to same two points of electrical circuit•Voltage same across each bulb•Total current divides among the parallel branches - equals sum of current in each branch - current in each branch inversely proportional to resistance of branch•Overall resistance of circuit lowered with each additional branch•Household wiring (and new Christmas light strings) designed in parallel - too many electrical devices on - too much current - trip fuse/breaker

ISNS 3371 - Phenomena of NatureWater Analogy for Parallel Circuits

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ISNS 3371 - Phenomena of Nature Determining Planet Mass and Orbit Animation