DEVIL PHYSICSTHE BADDEST CLASS ON

CAMPUSPRE-IB PHYSICS

GIANCOLI SECTION 5-8SATELLITES AND “WEIGHTLESSNESS”

Objectives Calculate the radius of a satellite’s

orbit given its height above the earth’s surface and the radius of the earth.

Understand that for any given velocity, there is only one distance from the center of the earth at which the satellite can remain in orbit.

Understand that for any given altitude, there is only one velocity at which the satellite can remain in orbit.

Objectives

Calculate the altitude at which a satellite must orbit for a given velocity.

Calculate the velocity at which a satellite must orbit for a given altitude.

Understand the meaning of ‘apparent weight’ and ‘apparent weightlessness’.

Girl in Elevator

FN

Fg

Girl in Elevator

FN

Fg

Elevator not moving

Acceleration zero

mgF

mgF

FF

FFmaa

maFF

maF

N

g

gN

gN

gN

00,0

Girl in Elevator

FN

Fg

Elevator moving up

Acceleration Positive

mgmaF

mgF

FmaF

maFF

maF

N

g

gN

gN

Girl in Elevator

FN

Fg

Elevator moving down

Acceleration Negative

mamgFmgmaF

mgF

FmaF

maFF

maF

N

N

g

gN

gN

Girl in Elevator

FN

Fg

Elevator cable breaks Girl plummeting to her

death, but remains calm

0

N

N

gN

gN

FmgmgF

FmgF

mgFFga

maF

Weightlessness

Weightlessness on a Motorcycle Motorcycle Jump

Weightlessness on Skis Ski Jump

Weightlessness in a Cage ?????

Weightlessness and Space

???

??? How do you keep from losing satellites?

Weightlessness and Space

FG mac

Weightlessness and Space

FG mac

Weightlessness and Space

2

2

rmMGF

rva

amF

maF

sEG

c

csG

c

FG mac

Weightlessness and Space

hrr e h

re

Weightlessness and Space

vr

GM

vrMG

rvm

rmMG

maF

maF

E

E

ssE

cG

c

2

2

2

FG mac

Weightlessness and Space

What happens if we change speed?

vr

GM

vrMG

rvm

rmMG

E

E

ssE

2

2

2

FG mac

Weightlessness and Space

If velocity increases, the force needed to keep the shuttle in orbit increases. Since the earth’s gravity doesn’t change, the shuttle will leave the circular orbit.

vr

GMrvm

rmMG

E

ssE

2

2

FG mac

Weightlessness and Space

If velocity decreases, the gravitational force is now stronger than the radial acceleration and it will pull the shuttle toward the earth, which will increase gravitational force, and the shuttle will be pulled down to the earth’s surface.

vr

GMrvm

rmMG

E

ssE

2

2

FG mac

Weightlessness and Space Only one speed for

a given orbit (radius)

Only one orbit (radius) for a given speed

rvGM

vr

GM

E

E

2

FG mac

Space Away From Earth

FG-Earth

FG-Moon

FG-Sun

Gravitational Force and Motion of Planets

Σary Review Can you calculate the radius of a

satellite’s orbit given its height above the earth’s surface and the radius of the earth?

Do you understand that for any given velocity, there is only one distance from the center of the earth at which the satellite can remain in orbit?

Do you understand that for any given altitude, there is only one velocity at which the satellite can remain in orbit?

Σary Review

Can you calculate the altitude at which a satellite must orbit for a given velocity?

Can you calculate the velocity at which a satellite must orbit for a given altitude?

Do you understand the meaning of ‘apparent weight’ and ‘apparent weightlessness’?

QUESTIONS?

Homework

#39-49