Transcript Two Observers See Different Things, but the Same Laws of Physics

Homework
 Work Mastering Physics Assignments
 Study for Exam
rotational motion
torque and angular momentum
static equilibrium
gravity
 Review Session - 7 PM - HL 188
 Work Reading Assignment for Friday
 Work on Lab Presentation
Example
 A 150 kg satellite is in circular orbit of radius 7.3 Mm
about the earth.
 Determine the potential energy.
U = -8.2 x109 J
 Determine the orbital speed.
v = 7400 m/s
 Determine the kinetic energy.
K = 4.1x109 J
 What is the escape speed from
this altitude?
Exercise
 Why are
rocket
launch sites
located
nearer to the
equator
(rather than
the poles)?
Angular Momentum
in the Bohr Model of the Atom
In the Bohr model:
The electron orbits like a
planet.
The electron can only have
certain values of angular
momentum.
L = n (h/2)
where n is an integer
Angular Momentum
in Quantum Mechanics
 L = l (l  1)
(h/2)
gives length of angular
momentum vector
 Lz = ml (h/2)
gives orientation of the
angular momentum
vector
The Bohr quantum
number
Lz

L
Quantum Numbers determine
the shape of the state
1s
2s
2p
l=0
for s-state
l=1
for p-state
l=2
for d-state
L = r x mv
Only s-states (L = 0) can
have electrons at the origin.
More Static Equlibrium

How does a truck scale work?

If the front wheels give a weight of 10000 N, the middle wheels
(which are 3 m back) give a weight of 30000 N and the rear
wheels (which are 10 m further back) give a weight of 25000 N,
where is the center of mass of the truck?
Opening the
paint can
A man tries to pry the lid off a can of
paint with a very light screwdriver.
 A force F is applied a distance L from
the edge of the can. The screwdriver
pushes up on the lid a distance d from
edge of the can.

What is the upward force on the lid?
 What is the normal force supplied by edge of the can on
the screwdriver?

Example
 If the wall is
frictionless,
the floor is
not, what are
the forces
acting on the
ladder?
Followup
 If the wall is
frictionless, the
coefficient of static
friction between
the ladder and the
floor is 0.8, how
large is the force
of static friction?
Example
 At what angle will the contents spill?
Example

A 9 m flagpole hangs in a horizontal
position from the side of a building. It is
supported by a hinge and a 15 m cable.
Find the tension in the cable and the
magnitude and direction of the force
supplied by the hinge if the flagpole
weighs 1500 N?