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PROJECTILES
Projectile Motion-Inertia and Falling Objects
http://www.youtube.com/watch?v=F92FQdnLlSc
Flaming piano tossed by trebuchet
Projectile Defined
Any object that moves through air or space
under the influence of gravity.
Horizontal Motion Associated
with a Projectile
Object is launched horizontally
Object continues in horizontal direction a constant
speed due to its inertia.
No increase or decrease in speed
Vertical Motion Associated with a
Projectile
Object’s motion is changed due to the force of
gravity.
Object increases or decreases in speed
Projectile Path Principles
The greater the object’s horizontal motion (or
speed), the wider the arc of its curved path.
If thrown from the same height, both projectiles
will land at the same time even if their horizontal
speeds are different.
See Figures 14.1 and 14.3 on page 263.
Constructing the path of a projectile: use
centimeters as scale
1 m = 1 cm
Horizontal Velocity = --- m/s
Calculate distance fallen using
d = 1/2gt2 , use rounded g = 10 m/s2
1s
2s
3s
4s
The Motion of a Curved Projectile
The motion of a curved projectile consists of two
components.
--Horizontal Motion
--Vertical Motion
This curve is called a parabola.
Horizontal Motion Associated
with a Projectile
Horizontal motion is initiated by an unbalanced force
Object continues in horizontal direction a constant
speed due to its inertia.
No increase or decrease in speed
Vertical Motion Associated with a
Projectile
Object’s motion is changed due to the force of
gravity.
Object increases or decreases in speed
Freefall Equations for Calculating the
Path of Projectile
Horizontal Motion
– For horizontal motion, assume a constant speed (equal
distance over equal time)
Vertical Motion
– Use freefall equations
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•
•
•
v = gt (how fast object falls)
d = ½gt2 (how far object falls)
t=
square root of 2d/g (how long it takes for an object to fall)
remember, g = 9.8 m/s2
Mapping the Path of a Projectile
Step One: Determine the horizontal velocity and how
far the object travels each second.
Step Two: Calculate how far the projectile falls for each
second that passes. Neglect air resistance.
Step Three: Assume 1 m = 1 cm and use this scale for
measuring string lengths and horizontal distances
Step four: Tape the strings on the meter stick at the
appropriate horizontal distances per second.
Applications
http://www.physicsclassroom.com/Class/vectors/
U3L2a.html