1. How I grade tests…
Remind class experiment 6 outside.
Demo of ball off table…
Demo projectile motion…

2. Class Notes 14 September Turn in HW Formal Lab (exp 05) assigned
Draw directions on vectors. 
Result: From tail of 1st to tip of last!
Answers like this are preferred:
R = 27 units at 145°
Formal Lab (exp 05) assigned
Today:
Projectile Motion
General 2D Motion

3. Pop Quiz: Two balls are on top of a table
Pop Quiz: Two balls are on top of a table. Ball A is dropped and ball B launched at some velocity. Which one hits the ground first?
The dropped ball.
The ball shot outward.
I choose not to vote.
Both hit at same time

4. Pop Quiz!
Two balls are on top of a table. Ball A is dropped and ball B launched at some velocity. Which one hits the ground first?
Why?
The answer is they hit at the same time. Motion in x and y are independent of each other.

5. For constant acceleration:
Notice that time connects the x and the y motion. Not saying that others variables can’t be equal at times (they certainly are, e.g. velocity at 45 degrees), but time must be equal. 5

6. Projectile Motion
A projectile is a body that is launched into some region which is then allowed to move freely.
For example, on the Earth!
ax = 0, ay = –g
We can (and will) treat the x and y
motions independently. 6

7. Example
A ball rolls off a 86.0-cm tall table and lands 52.0 cm away. What was its velocity before leaving the table and as it hits the ground?
Use photogate to get initial speed = mm / s = 1.35 m/s
1.24 m/s at 0°
, 4.29 m/s at –73.2°

8. Example
A ball is shot into the air with an initial velocity of 50.0 m/s at °. Find the total time the projectile is in the air, the horizontal displacement, maximum altitude, and final velocity. (Take g=10. m/s2)
Along the way, show that this is parabolic motion. y = 30t–5t2, x = voxt  y = Ax–Bx2
Also, let students throw koosh ball to each other and observe the parabola, opening downward.
6.0s, 240m, 45m,

9. Homework Continue reading Chapter 3, up to section 7.
HW#11: Do problems on Worksheet 11
HW#12: Test rework due 9/19
Formal Lab – exp5 – Sep 26