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# PH 121 8.3-8.5 class mini lecture

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## Richard Datwyler

on 30 May 2018

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#### Transcript of PH 121 8.3-8.5 class mini lecture

8.3-8.5
In class principle summary
review fair ride.
Orbits are extended projectile motion

Only force acting on orbiting object is gravity, thus in
free Fall motion

Orbital speed and period is

Note g can change
For this chapter stay close to earth and
g = 9.8

8.3: Circular Orbits
8.4: Fictitious Forces
Really just
Newton’s 1st law
application

Happen because not in
inertial reference frame

Examples of water in bucket and roller coasters

Effect on gravity
g=9.83 - inertial effect (.033) = g = 9.80
Small enough we will
neglect rotational effects

Kinematic equations
of motion in rotational reference frame

Dynamics
in Nonuniform Circular Motion

Find total Force/acceleration using Pythagorean theorem

8.5: Nonuniform Circular Motion
Questions?
Quiz
Orbital velocity depends upon:
1. Mass of satellite 2. Mass of planet
3. Acceleration due to gravity
4. Radius 5. Rotation of planet

A. 1,3,5
B. 1,2,3,4
C. 2,3,4
D. 1,2,4,5
E. 3,4
F. 1,2,5
The earth is a perfectly good Inertial reference frame.

A. True (because it is)
B. False (no but we use it any way)
Water stays in a bucket as you swing it around your head because:

A. It is an application of Newton's 3rd law
B. The centrifugal force acts on it
C. Its inertia is keeps it there
D. The bottom of the bucket pulls it up
E. Vanderwall attraction
F. It is frozen and stuck in bucket
Non uniform circular motion problems are:

A. Solvable using circular kinematic equations
B. Can't be solved unless transformed into linear terms
C. Are just simply too hard to solve, give up.
#60 Father stands on conical 20 degree hill and spins his 20 kg child on a 5.0 kg cart, with 2 meter rope. Friction is negligible and speed is 14 rpm, what is tension
Example
20
0
20
20
0
0
G
N

F
F
T
20
0
2 m
radius = r = 2 cos(20) = 1.88