In the news …. Bit of Administration …. ReadingReading –Bless, pp. 105-139 –BNSV, pp. 70-83 Observing LabObserving Lab –Start Lab 2 on Saturday Timing

In the news …In the news …

Bit of Administration ….Bit of Administration ….

• ReadingReading– Bless, pp. 105-139Bless, pp. 105-139– BNSV, pp. 70-83BNSV, pp. 70-83

• Observing LabObserving Lab– Start Lab 2 on SaturdayStart Lab 2 on Saturday

• Timing Matters! Must be nearly same time every night.Timing Matters! Must be nearly same time every night.

• 10 minutes every clear night for two weeks.10 minutes every clear night for two weeks.

Kepler’s Three Laws of Planetary Kepler’s Three Laws of Planetary MotionMotion

1.1. The Orbits of the Planets are Ellipses with the The Orbits of the Planets are Ellipses with the Sun at One FocusSun at One Focus

Which of the following orbits has the smallest eccentricity?

A) B) C)

D) All have the same eccentricity.

ConcepTest!ConcepTest!

e = 0 e = 0. 4 e = 0.8

Which of the following orbits has the smallest semi-major axis?

A) B) C)

D) All have the same semi-major axis.



2.2. The Line Joining The Sun and A Planet The Line Joining The Sun and A Planet Sweeps Out Equal Areas in Equal TimesSweeps Out Equal Areas in Equal Times

30 days 30 days

The Earth is somewhat closer to the Sun in (northern) winter than The Earth is somewhat closer to the Sun in (northern) winter than in summer. Kepler’s Second Law tells us that the Sun should in summer. Kepler’s Second Law tells us that the Sun should appear in winter toappear in winter to

A.A. Move faster west to east during each day.Move faster west to east during each day.B.B. Move faster east to west during each day.Move faster east to west during each day.C.C. Move slower west to east during each day.Move slower west to east during each day.D.D. Move slower east to west during each day.Move slower east to west during each day.



3.3. The Square of a Planet’s Period (P in Years) The Square of a Planet’s Period (P in Years) Equals the Cube of the Semi-Major Axis of its Equals the Cube of the Semi-Major Axis of its Orbit (A in AU)Orbit (A in AU)

PP22 = A = A33

P P 22 = A = A 33

A

1

Comet Halley has an orbital period of 76 years. Its semi-major axisComet Halley has an orbital period of 76 years. Its semi-major axisisis

A) less than the semi-major axis of the orbit of the EarthA) less than the semi-major axis of the orbit of the Earth B) less than the semi-major axis of the orbit of MarsB) less than the semi-major axis of the orbit of Mars C) less than the semi-major axis of the orbit of NeptuneC) less than the semi-major axis of the orbit of Neptune D) unknown without information about the orbital eccentricityD) unknown without information about the orbital eccentricity


1

A

The Birth of Modern PhysicsThe Birth of Modern Physics• Aristotle ReduxAristotle Redux

A body at rest stays at rest; a body in motion will come to rest.A body at rest stays at rest; a body in motion will come to rest.Rest is the natural state of matterRest is the natural state of matter

Movement happens only in the presence of a forceMovement happens only in the presence of a force

• Galileo - The Father of Experimental PhysicsGalileo - The Father of Experimental Physics

Law of InertiaLaw of InertiaBodies in undisturbed motion stay in motionBodies in undisturbed motion stay in motion

(But celestial bodies move with uniform circular motion,(But celestial bodies move with uniform circular motion,being imbued with “circular inertia”)being imbued with “circular inertia”)

The Birth of Modern PhysicsThe Birth of Modern Physics• Mechanics - The Study of Motions and ForcesMechanics - The Study of Motions and Forces

– Fundamental ConceptsFundamental Concepts

• MassMass - Amount of matter - Amount of matter

• InertiaInertia - Property of matter requiring a force to change motion - Property of matter requiring a force to change motion “ “Resistance to Force”Resistance to Force”




• InertiaInertia - Property of matter requiring a force to change motion - Property of matter requiring a force to change motion

• PositionPosition - Location in space - Location in space - Absolute reference frame; a Cartesian concept- Absolute reference frame; a Cartesian concept

• VelocityVelocity - Rate at which position changes - Rate at which position changes - Defined by both speed and direction- Defined by both speed and direction

• AccelerationAcceleration - Rate at which velocity changes - Rate at which velocity changes

The Birth of Modern PhysicsThe Birth of Modern Physics


– Change of SpeedChange of Speed1.1. Parked car: Acceleration = 0 (km/hr)/secParked car: Acceleration = 0 (km/hr)/sec2.2. Car at constant speed of 100 km/hr: Acceleration = 0 (km/hr)/secCar at constant speed of 100 km/hr: Acceleration = 0 (km/hr)/sec3.3. Car going from 0 km/hr to 100 km/hr in 10 secondsCar going from 0 km/hr to 100 km/hr in 10 seconds

Acceleration = (change in velocity)/(change in time)Acceleration = (change in velocity)/(change in time) = 100 km/hr / 10 sec= 100 km/hr / 10 sec = 10 (km/hr)/sec= 10 (km/hr)/sec

4.4. Drop a ball …Drop a ball …

• Acceleration - Rate at which velocity changesAcceleration - Rate at which velocity changes


t (sec) d v a

0 0 cm 0 cm/sec

1 490 cm 980 cm/sec 980 (cm/sec)/sec



You throw a ball straight up in the air. It goes up, momentarily You throw a ball straight up in the air. It goes up, momentarily stops, and then falls back toward you. During its flightstops, and then falls back toward you. During its flight

A.A. The ball is accelerating at all timesThe ball is accelerating at all timesB.B. The ball is accelerating except for that moment when it stopsThe ball is accelerating except for that moment when it stopsC.C. The ball is only accelerating on the way back downThe ball is only accelerating on the way back downD.D. The ball is never acceleratingThe ball is never accelerating


The Birth of Modern PhysicsThe Birth of Modern Physics• AristotleAristotle

Heavy objects fall fasterHeavy objects fall faster

• GalileoGalileo

All objects fall at the All objects fall at the samesame constant acceleration constant acceleration

The Birth of Modern PhysicsThe Birth of Modern Physics• Acceleration - Rate at which velocity changesAcceleration - Rate at which velocity changes

– Change of DirectionChange of Direction

10 km/hr

10 km/hr




• InertiaInertia - Property of Matter Requiring a Force to Change Motion - Property of Matter Requiring a Force to Change Motion

• PositionPosition - Location in space - Location in space - Absolute reference frame a Cartesian concept- Absolute reference frame a Cartesian concept

• VelocityVelocity - Rate at which position changes - Rate at which position changes - Identified by both speed and direction- Identified by both speed and direction


• Central ForceCentral Force

The Birth of Modern PhysicsThe Birth of Modern Physics• Central ForceCentral Force

FFcc = m v = m v22 / R / RRR

mm vv


• Central ForceCentral Force

FFcc = m v = m v22 / R / R

You are holding your little brother by his hands and swinging him You are holding your little brother by his hands and swinging him around you. To increase his “excitement”, you begin to swing around you. To increase his “excitement”, you begin to swing him faster. You have to grip his hands more tightly becausehim faster. You have to grip his hands more tightly because

A.A. His mass has increased with the increased speedHis mass has increased with the increased speedB.B. The radius of his circle around you has increasedThe radius of his circle around you has increasedC.C. You need to provide more central force to keep him moving in You need to provide more central force to keep him moving in

a circlea circleD.D. You need to pull harder to keep him in a circle.You need to pull harder to keep him in a circle.E.E. Both C and DBoth C and D



• Central Force Central Force (also known as(also known as Centripetal Force Centripetal Force))

– Central force required to keep object moving in a circleCentral force required to keep object moving in a circle

FFcc = m v = m v22 / R / R

The Birth of Modern PhysicsThe Birth of Modern Physics• NewtonNewton 1700 AD1700 AD

1665-1666 plague was sweeping England … left Cambridge for home … 1665-1666 plague was sweeping England … left Cambridge for home … in next five years he developed his ideas on ….in next five years he developed his ideas on ….

MechanicsMechanicsGravityGravityCalculusCalculus

Discovered Spectrum of LightDiscovered Spectrum of LightTheory of LightTheory of Light

Reflecting TelescopeReflecting Telescope

Newton’s Laws of MotionNewton’s Laws of Motion

1.1. A Body Remains at Rest or Moves at UniformA Body Remains at Rest or Moves at Uniform

Speed in a Straight Line unless acted Upon bySpeed in a Straight Line unless acted Upon by

a Force.a Force.

The little brother that you are swinging around is beginning to The little brother that you are swinging around is beginning to annoy you. So you let go! After you let go, he willannoy you. So you let go! After you let go, he will

A.A. Continue to travel in a circle until he hits the groundContinue to travel in a circle until he hits the groundB.B. Travel in a spiral pattern away from you until he hits the Travel in a spiral pattern away from you until he hits the

groundgroundC.C. Travel in a straight line until he hits the groundTravel in a straight line until he hits the groundD.D. Drop to the ground right where you let go of himDrop to the ground right where you let go of him


The Birth of Modern PhysicsThe Birth of Modern Physics• Central ForceCentral Force


2.2. The Change of Motion is Proportional to theThe Change of Motion is Proportional to the

Force Acting on it and in the Direction of the Force Acting on it and in the Direction of the ForceForce

F = m aF = m a


t (sec) d v a

0 0 0




Fgravity

Change of DirectionChange of Direction

10 km/hr

10 km/hr

F

Consider again the falling ball with constant accleration. From this Consider again the falling ball with constant accleration. From this experiment we know that experiment we know that

A.A. The force of gravity increases closer to the groundThe force of gravity increases closer to the groundB.B. The force of gravity is constant over the distance the ball dropsThe force of gravity is constant over the distance the ball dropsC.C. The force of gravity decreases closer to the groundThe force of gravity decreases closer to the ground



3.3. To Every Action there is an Equal and To Every Action there is an Equal and Opposite ReactionOpposite Reaction


3.3. To Every Action there is an Equal and To Every Action there is an Equal and Opposite ReactionOpposite Reaction

• Recoil of a gunRecoil of a gun

• CollisionsCollisions

• RocketsRockets

You are an astronaut taking a spacewalk to fix your spacecraft You are an astronaut taking a spacewalk to fix your spacecraft with a hammer. Your lifeline breaks and the jets on your back with a hammer. Your lifeline breaks and the jets on your back are out of fuel. To return safely to your spacecraft you shouldare out of fuel. To return safely to your spacecraft you should

A.A. Throw your hammer at your spacecraft to get someone’s Throw your hammer at your spacecraft to get someone’s attentionattention

B.B. Throw your hammer away from the space shipThrow your hammer away from the space shipC.C. Use a swimming motion with your armsUse a swimming motion with your armsD.D. Kiss your spacecraft good byeKiss your spacecraft good bye


Documents

In the news …. Bit of Administration …. ReadingReading –Bless, pp. 105-139 –BNSV, pp. 70-83 Observing LabObserving Lab –Start Lab 2 on Saturday Timing