Chapter 3
Projectile Motion
Projectile Motion
• Previously, we studied motion in one direction
(linear motion)
• Projectiles follow a curved path
(nonlinear motion)
The velocity of a projectile has both vertical and
horizontal components to its motion that are
independent of each other.
Vectors
• A scalar quantity has only magnitude
Ex. 70 mph
• A vector quantity has both magnitude and
direction
Ex. 70 mph, North
In physics an arrow is drawn to represent a vector.
The length of the arrow is proportional to the
magnitude of the vector and the arrow shows the
direction.
Components of Vectors
80 km/hr
60 km/hr
• “Any vector can be “resolved” into two component vectors at right
angles to each other.
• “These two vectors are known as components of the given vector
they replace.” - p. 31
Vertical Distance
Horizontal Distance
• Each box represents one
time interval (Ex. 1 sec)
• Purple dots represent the
horizontal position (top),
vertical position (left side)
and position in space
(curved line) of a
projectile.
• Notice that the horizontal speed of the projectile remains constant
• The vertical speed of the projectile acts like an object in free-fall
• The only force acting on our projectile is gravity (neglecting air
resistance)
Vertical Distance
Horizontal Distance
• The Horizontal Distance
vs. time that a projectile
will travel will be constant:
Distance = Velocity x Time
• The vertical Distance vs
time that a projectile will
fall will follow the
equation d=½gt2
(Note this applies only if a
projectile is dropped from
rest. If there is an initial
velocity, we have to use
the expanded equation:
d= vit + ½gt2)
• Suppose a ball is rolled off of a cliff
horizontally with a speed of 5 m/s
Example 1
• How long will it take the ball to hit the
ground?
123 Meters
d=½gt2
123 = ½(9.81)(t2)
t= 5s
• How fast was the ball traveling in the
downward direction when it hit the ground?
v = gt
v = (9.81)(5) = 49 m/s
• How fast in the horizontal direction was the
ball traveling when it hit the ground? 5 m/s
• How far from the cliff will the ball land?
Distance = Velocity x Time
Distance = (5 m/s)(5s) = 25 meters