1. Class Notes 20 October Turn in FBDs / Pick up HW Today:
Do NOT rotate your FBDs!!!
#5: Use SFy=0, SFx=max twice?
Start with FBD, SFy=0, SFx=max.
Today:
Midterm grades…
Banking a turn.
Universal Gravitational Force.

3. This graph proves Newton’s second law, showing that acceleration and mass are directly related.
Yes No
Partially correct
Who is this Newton of whom you speak?
2016 Vote: 6, 3, 6, 0
First off the word “proves” is incorrect. The mass on the abscissa refers to the hanging mass, which directly affected the tension. This graph shows that acceleration is directly related to force.

4. Examples
How fast may a car travel when negotiating a turn if the radius of curvature is 150. ft and s=0.600?
Use N2 to find v = 36.7 mph
If no friction is present, what
must be done?
Bank the turn at an angle of
q = 31.0º

7. Universal Gravitational Force
Proposed by Newton in the Principia
Force is proportional to what?
|Fgrav|=Gm1m2/r2
Newton couldn’t determine G
1/r2 is need to give planets
elliptical orbits.
For “point” masses, but…

8. Universal Gravitational Force
Force is always attractive
FAB = –FBA (N3)
Universal effect
Spherical objects are treated
Worked for our solar system,
except Mercury…
We can use this law to find g
Responsible for stars, …
Attractive: Force between you and your physics book

9. 1 light year (6 trillion miles)
1 light year (6 trillion miles)
Star formation
Eggs: (Evaporating Gaseous Globules). Hydrogen gas is gathered together by gravitational force. Sharp points are where stars are formed. Scale is about 1 light-year (6 trillion miles) top to bottom. Notice picture on “Star Birth” poster above board; picture taken by the Hubble space telescope.

10. Universal Grav. Constant
Henry Cavendish
Universal!
1798, Used torsion balance to calculate the Earth’s density
G = 6.67  10–11 Nm2/kg2
Apparent Weight
Often FN but opposite direction
Satellites…
“Weightless”  Only Fgrav acts
Satellites, such as the moon

11. Three quarters are placed on the rotational platform at different radii. Which will slip first?
inside
middle
outside
All at the same time
2016 Vote: 4, 0 ,11, 0
The outside one slips first. The centripetal force holding it on is friction, which is the same for all quarters. The one on the outside is moving faster, and the radial acceleration depends on v *squared*.

12. Three coins are placed on the rotational platform, all at the same radius. Which will slip first?
penny
dime
quarter
All at the same time
2016 Vote: 3, 9, 1, 2
All coins slip at the same time. Setting the frictional force equal to maR, we find the mass divides out. The frictional coefficient of all coins is approximately the same.

13. Homework For Monday: Lab next Thursday Test next Frisday
Finish reading Chapter 5
Do problems on worksheet 23:
Lab next Thursday
Derivations for experiment 10
Test next Frisday
Physics is cumulative
Test 3: Chapters 4 and 5