1. AP PHYSICS B www.lodiscience.com
Mr. Dove
Room 217
Course Help:Mondays/Wednesdays/Fridays
After School or Before School by Appointments

2. Course Information

3. Succeeding in AP Physics
Do your homework (yourself)!
Get help A.S.A.P. when you feel lost!
Make sure you understand both “why” and “why not”
Interrupt the lecturer!
Study, Study, Practice, Practice, Study and Practice some more, Then Study so you can practice!

4. Mechanics Half the course Quantified largely by Galileo
Problems involve: velocity, acceleration, mass, momentum, energy, torque, angular momentum, moment of inertia…

5. UNITS (Systéme Internationale)
Dimension
SI (mks) Unit
Definition
Length
meters (m)
Distance traveled by light in 1/(299,792,458) s
Mass
kilogram (kg)
Mass of a specific platinum-iridium allow cylinder kept by Intl. Bureau of Weights and Measures at Sèvres, France
Time
seconds (s)
9,192,631,700 oscillations of cesium atom

6. Standard Kilogram at Sèvres

7. Dimensional Analysis Dimensions & units can be treated algebraically.
Variable from Eq. x m t
v=(xf-xi)/t
a=(vf-vi)/t
dimension L M T
L/T
L/T2

8. Dimensional Analysis Checking equations with dimensional analysis:
(L/T2)T2=L L
(L/T)T=L
Each term must have same dimension
Two variables can not be added if dimensions are different
Multiplying variables is always fine
Numbers (e.g. 1/2 or p) are dimensionless

9. Example 1.1 Check the equation for dimensional consistency:
Here, m is a mass, g is an acceleration, c is a velocity, h is a length

10. Example 1.2 Consider the equation:
Where m and M are masses, r is a radius and v is a velocity.
What are the dimensions of G ?
L3/(MT2)

11. Example 1.3
Given “x” has dimensions of distance, “u” has dimensions of velocity, “m” has dimensions of mass and “g” has dimensions of acceleration.
Is this equation dimensionally valid?
Yes
Is this equation dimensionally valid? No

12. Units vs. Dimensions Dimensions: L, T, M, L/T …
Units: m, mm, cm, kg, g, mg, s, hr, years …
When equation is all algebra: check dimensions
When numbers are inserted: check units
Units obey same rules as dimensions: Never add terms with different units
Angles are dimensionless but have units (degrees or radians)
In physics sin(Y) or cos(Y) never occur unless Y is dimensionless

13. Example 1.3 Grandma traveled 27 minutes at 44 m/s.
How many miles did Grandma travel?
44.3 miles

14. Prefixes
In addition to mks units, standard prefixes can be used, e.g., cm, mm, mm, nm

15. Example 1.4a The above expression yields: 40.11 m 4011 cm A or B
Impossible to evaluate (dimensionally invalid)

16. Example 1.4b The above expression yields: 4.5 m kg 4.5 g km A or B
Impossible to evaluate (dimensionally invalid)

17. Example 1.4b The above expression yields: -1.5 m -1.5 kg m2 -1.5 kg
Impossible to evaluate (dimensionally invalid)