phys16 – lecture 29
DESCRIPTION
PHYS16 – Lecture 29. Ch. 13 Gravitation. This Week. Newton’s law of Gravity Gravitational Potential Energy Satellites Kepler’s Laws of Planetary Motion Orbital Shape Orbital Areas Orbital Period. Cavendish Experiment. Uses a torsional pendulum F= GMm /r 2. Satellites. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/1.jpg)
PHYS16 – Lecture 29
Ch. 13 Gravitation
![Page 2: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/2.jpg)
This Week
• Newton’s law of Gravity• Gravitational Potential Energy• Satellites• Kepler’s Laws of Planetary Motion– Orbital Shape– Orbital Areas– Orbital Period
![Page 3: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/3.jpg)
Cavendish Experiment
Uses a torsional pendulumF=GMm/r2
![Page 4: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/4.jpg)
Satellites
![Page 5: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/5.jpg)
Centripetal Force and Gravity
• For an object (like a satellite) in circular motion due to gravity
Fc = FG
http://qwickstep.com/search/earth-orbit-around-the-sun.html
rGMv
rMmGma
FF
c
Gc
2
2
![Page 6: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/6.jpg)
Example Question: Moon Energy
• If the Moon-Earth distance were to shrink what would happen to the Moon’s kinetic energy?
A) IncreaseB) Stay the sameC) Decrease
![Page 7: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/7.jpg)
Example Question: Moon Period
• If the Moon-Earth distance were to shrink what would happen to the period of the moon?
A) Increase (Greater than ~28 days)B) Stay the same at ~28 daysC) Decrease (Less than ~28 days)
![Page 8: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/8.jpg)
Orbital Energy
• Gravitational potential energy increases as distance increases
• Kinetic energy decreases as distance increases• So, why do higher orbitals have more energy?
rGMmE
rGMm
rGMm
rGMmmvE
UKE
2
221 2
![Page 9: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/9.jpg)
Example Question: Satellite
• A Satellite orbiting the Earth in a circular orbit wants to go to a lower orbit. What should the satellite do?
A) Nothing. It is falling toward the earth.B) Turn on rocket thrusters to accelerate, moving to a lower orbital.C) Turn on rocket thrusters to decelerate, moving to a lower orbital
![Page 10: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/10.jpg)
Escape velocity
• Minimum velocity needed to “escape” the gravitational force
RGMv
RGMmmv
UUKKE
i
i
ifif
2
0)0()210(
0)()(
2
![Page 11: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/11.jpg)
Discussion: Launching Rockets
• When launching a rocket to escape the Earth’s gravity, does the mass of the rocket matter? Why or why not?
The escape velocity does not depend on mass. Butthe kinetic energy does. Thus, a more massive rocketrequires more fuel.
![Page 12: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/12.jpg)
Discussion: Launching Rockets
• When launching a rocket to escape the Earth’s gravity, does the mass of the rocket matter? Why or why not?
• Which planet has the smallest escape velocity?
Mercury!
![Page 13: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/13.jpg)
Discussion: Launching Rockets
• When launching a rocket to escape the Earth’s gravity, does the mass of the rocket matter? Why or why not?
• Which planet has the smallest escape velocity?
• What would be the escape velocity of a black hole?
Infinity!
![Page 14: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/14.jpg)
Disscussion: Launching Rockets
• When launching a rocket to escape the Earth’s gravity, does the mass of the rocket matter? Why or why not?
• Which planet has the smallest escape velocity?• What would be the escape velocity of a black hole?• Does the direction of launch from the earth matter?
Why or why not?
Want to launch eastward to take advantage of the Earth’srotational velocity. Also want to launch along Earth’s orbitalpath, as well.
![Page 15: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/15.jpg)
Discussion: Launching Rockets
Launch with Earth’s rotationLaunch with Earth’s orbital
![Page 16: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/16.jpg)
Discovery Launch
• http://www.youtube.com/watch?v=4FROxZ5i67k
http://www.intothemusic.biz/wp-content/uploads/2010/04/space_shuttle_launch.jpg
![Page 17: PHYS16 – Lecture 29](https://reader036.vdocument.in/reader036/viewer/2022081517/56816728550346895ddbc495/html5/thumbnails/17.jpg)
Main Points
• Satellites– Escape velocity depends on the gravitational field
of planet– Launch with rotational and orbital velocity of Earth