Physics LG
Jan. 30, 2009
Vectors &
Projectile Motion
Motion is Relative
► Frame
of Reference - perspective from
which you observe
Truck at Rest
If the ball is thrown at 60 km/h relative to
the truck, at what velocity will the person
catch the ball at?
Truck Moving Away
► If
the ball is thrown at 60 km/h west relative to
the truck and the truck moves at 40 km/h east
relative to the catcher, at what velocity will the
person catch the ball at?
Truck Moves Towards
► If
the ball is thrown at 60 km/h west relative to
the truck and the truck moves at 40 km/h west
relative to the catcher, at what velocity will the
person catch the ball at?
► Scalar
- measurement of magnitude only
 Ex) mass, volume, speed
► Vector
- measurements with both
magnitude and direction
 Ex) velocity, acceleration, force
Vectors
arrowhead = direction
length of arrow = magnitude
Vector addition
Resultant – sum of vectors
Pythagorean Theorem
a2 + b2 = c 2
► c2
►
►
►
►
= a2 + b2
c2 = 802 + 602
c2 = 6400 + 3600
√c2 = √10,000
c = 100 km/hr
Example Problem
► c2
►
►
►
►
= a 2 + b2
c2 = 42 + 32
c2 = 16 + 9
c2 = 25
c = 5 km/h
Vector addition
►
Pythagorean Theorem -
►
Parallelograms -
►
Head-to-tail method -
►
Trigonometry -
Vector Addition
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=51
What is the vertical and horizontal
component of a vector?
http://www.batesville.k12.in.us/Physics/APPhyNet/Vectors/Hor_&_Vert_Comps.html
Projectile Motion
Projectile – an object moving through air
affected by gravity
Projectile Demos
► Shooter/
Dropper
► Monkey and Hunter
Projectile Motion
Horizontal and vertical motion act independently
d x  vt
1 2
d y  at
2
How fast is the ball thrown?
► Vertical
► Horizontal
► d=
► v=
.5at2
► 5 = .5(10)t2
► t= 1 second
d/t
► v= 20m/1s
► v= 20 m/s
The ball is thrown at 20 m/s!
Upwardly-Moving Projectiles
What angle should
a ball be kicked to
get the farthest?
Projectiles launched at the same
speed but different angles.
Shot Put - 45º is not the ideal angle, why?
You are already off the ground 1-2 meters.
45º is the ideal angle for high speed
projectiles either. Why?
Air resistance must be considered.
Fast Moving Projectiles
► What
would happen if you threw a ball so fast that
the curvature of the earth came into play?
Fast Moving Projectiles
► Satellite-
a projectile traveling fast enough to fall
around the earth rather than into
► To
stay in orbit around the earth, a satellite needs
to travel at 8 km/s!
Hang Time
Due Next Week
 POTW
 11s Bull’s eye lab
 12s Rocket Lab
 30s Motion Worksheet #1
 31s Motion Worksheet #2
 32s Motion Review
 Test will be next Thursday Feb 5th
►Study the 1s, 2s, labs, and worksheets
►Use the back page of booklet under
motion for note sheet for test.