Transcript Lecture 7

• Please sit together
in pairs:
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– Alexandra and Jiayuan
Onyema and Michael
– David and Erica
Alejandra and Honglu
– Abigael and Dian
Chris and Matt
Ryan and Lin
John F. and Anwen
Walter and Mengyue
Max and Melissa
Amanda and Zhongyun
Pauline and Kaijun
Jake and Erich
John W. and Irfan
Jennifer and Jason
Phys 150 Lecture 7
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Announcements
• Homework 4 is due on Sunday at
midnight.
• Please check your quiz, homework (and
reports), and i>clicker scores on the
Gradebook. Email me if there are any
problems.
• James Scholar honors project: email me
Phys 150 Lecture 7
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Announcements
• Guidelines for essays are posted on the
course web page. Your essay should
– Answer the question
– Contain reasoned arguments
– Contain relevant facts/numbers from the
book/lecture
– Consider a broad range of solutions
– Have correct spelling and grammar
Phys 150 Lecture 7
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Chapter 3 – Gravity, Force, Space
• On the surface of the Earth, everything
falls with acceleration g=10 (m/s)/s
Feather and coin
Phys 150 Lecture 7
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Chapter 3 – Gravity, Force, Space
• On the surface of the Earth, everything
falls with acceleration g=10 (m/s)/s
Feather and coin
Apollo 15 1971
Phys 150 Lecture 7
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i>clicker question
The acceleration due to gravity on the
moon (gmoon) is about
A.
B.
C.
D.
2g
g/2
g/6
g/200
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i>clicker question
The acceleration due to gravity on the
moon (gmoon) is about
A.
B.
C.
D.
2g
g/2
g/6
g/200
Phys 150 Lecture 7
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i>clicker question
An astronaut is floating inside a
spaceship that is drifting through space.
The spaceship begins to fall, nose first,
toward a planet. The astronaut
A. is pushed toward the front of the ship
B. is pushed toward the rear of the ship
C. continues to float inside the ship
Phys 150 Lecture 7
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i>clicker question
An astronaut is floating inside a
spaceship that is drifting through space.
The spaceship begins to fall, nose first,
toward a planet. The astronaut
A. is pushed toward the front of the ship
B. is pushed toward the rear of the ship
C. continues to float inside the ship
Phys 150 Lecture 7
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i>clicker question
A satellite in low Earth orbit (LEO) is
travelling at about
A.
B.
C.
D.
50 miles/hour
5 miles/sec
500 meters/sec
It depends a lot on its altitude
Phys 150 Lecture 7
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i>clicker question
A satellite in low Earth orbit (LEO) is
travelling at about
A.
B.
C.
D.
50 miles/hour
5 miles/sec
500 meters/sec
It depends a lot on its altitude
-
5 miles/sec at an altitude around 100 miles
Earth radius is 4000 miles
Spy satellites can only view a given area for
about a minute
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Spy satellite photo
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International Space Station
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Landsat
GRACE
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i>clicker question
A satellite in geosynchronous orbit is
about how far above the surface of the
Earth?
A.
B.
C.
D.
1200 miles
12,000 miles
22,000 miles
120,000 miles
Phys 150 Lecture 7
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i>clicker question
A satellite in geosynchronous orbit is
about how far above the surface of the
Earth?
A.
B.
C.
D.
1200 miles
12,000 miles
22,000 miles
120,000 miles
-
22,000 miles is more than 5 Earth radii
geosynchronous orbit is above the equator
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Geosynchronous weather satellite
Also great for communication satellites
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Space debris
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i>clicker question
There are relatively few satellites in
medium earth orbit (MEO) because
A.
B.
C.
D.
they are not geosynchronous
they are too high to make good spy satellites
they are mostly GPS satellites
All of the above
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i>clicker question
There are relatively few satellites in
medium earth orbit (MEO) because
A.
B.
C.
D.
they are not geosynchronous
they are too high to make good spy satellites
they are mostly GPS satellites
All of the above
- GPS = Global Positioning System uses about 24
MEO satellites at an altitude of 12,000 miles.
They orbit the Earth every 12 hours.
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GPS
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i>clicker question
To escape completely from the Earth, a
rocket must attain a minimum velocity of
A.
B.
C.
D.
5 miles/sec
7 miles/sec
20 miles/sec
32 miles/sec
Phys 150 Lecture 7
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i>clicker question
To escape completely from the Earth, a
rocket must attain a minimum velocity of
A.
B.
C.
D.
5 miles/sec
7 miles/sec
20 miles/sec
32 miles/sec
-
5 miles/sec is LEO
7 miles/sec is escape velocity
20 miles/sec is the velocity of the Earth
around the sun
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i>clicker question
A car travelling 60 mph collides with a
bus travelling 20 mph. The force of the
car on the bus is
A.
B.
C.
D.
Less than the force of the bus on the car
Greater than the force of the bus on the car
Equal to the force of the bus on the car
It depends on whether the collision is head-on
or from the rear
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i>clicker question
A car travelling 60 mph collides with a
bus travelling 20 mph. The force of the
car on the bus is
A.
B.
C.
D.
Less than the force of the bus on the car
Greater than the force of the bus on the car
Equal to the force of the bus on the car
It depends on whether the collision is head-on
or from the rear
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Newton’s Third Law
• Forces always come in pairs
– Every “action” has an equal and opposite
“reaction”
Skateboard
Balloon
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