Projectile Motion
Motion In Two Dimensions
We restrict ourselves to objects thrown near the Earth’s surface so that gravity
can be considered constant.
Projectile motion is a form of motion in which an object
called a projectile is thrown and moves along a curved
path under the action of gravity only.
The motion of a projectile is determined only by the object’s
initial velocity and gravity.
Projectile motion applies to sports.
Projectile motion applies to destructive
projectiles.
Projectile motion is a combination of horizontal motion and
vertical motion.
The horizontal motion of a projectile is constant because no
gravitational force acts horizontally
The vertical motion of a projectile is nothing more than free fall
with a constant downward acceleration due to gravity.
The vertical motion of a projected object is
independent of its horizontal motion.
A projectile moves horizontally with constant velocity
while being accelerated vertically. The result is a motion
in a curved path.
The path of a projectile is called its
trajectory.
The trajectory of a projectile in free fall
is a parabola.
A projectile, once projected, continues in
motion by its own inertia and is influenced
only by the downward force of gravity.
An object projected
horizontally will
reach the ground in
the same time as
an object dropped
vertically.
No matter how
large the horizontal
velocity is, the
downward pull of
gravity is always
the same.
The cannonball falls the same amount of distance as it did
when it was merely dropped from rest
PROJECTILE MOTION
in
TWO DIFFERENT
CASES
Horizontally launched projectile
Horizontal velocity is constant. Vertical velocity is changing
due to gravitational acceleration..
Vertically launched projectile
The horizontal velocity component remains the same size
throughout the entire motion of the cannonball.
A ball kicked at an
angle
Sample Problem 1
A ball rolls off a desk at a speed of 3.0 m/s
and lands 0.50 seconds later.
• How far from the base of the desk does the
ball land?
• How high is the desk?
• What is the speed and angle of impact?
Sample Problem 2
A cannon fires a cannonball 500.0 m
downrange when set at a 45.0o angle. At what
velocity does the cannonball leave the
cannon?
Factors Affecting Projectile Motion
• What two factors would affect projectile
motion?
– Angle
– Initial velocity
Initial
Velocity
Angle
Projectiles launched at different angles.
Sports Trivia
Maximum range is achieved if the projectile is
fired at an angle of 45 degrees with respect to
the horizontal.
In Conclusion
A projectile is any object upon which the only force
is gravity.
Projectiles travel with a parabolic trajectory due to
the influence of gravity.
There are no horizontal forces acting upon projectiles
and thus no horizontal acceleration.
The horizontal velocity of a projectile is constant.
there is a vertical acceleration caused by gravity
(-9.8 m/s).
The horizontal motion of a projectile is independent
of its vertical motion.
Test your knowledge
Suppose a snowmobile is equipped with a
flare launcher which is capable of launching
a sphere vertically. If the snowmobile is in
motion and launches the flare and maintains a
constant horizontal velocity after the launch,
then where will the flare land (neglect air
resistance)?
Test your knowledge
Suppose an airplane drops a flare while it
is moving at constant horizontal speed at
an elevated height. Assuming that air
resistance is negligible, where will the flare
land relative to the plane?
A. Directly below the plane.
B. Below the plane and ahead of it.
C. Below plane and behind it.
Why does the horizontal component of a
projectile’s motion remain constant?
Because no force acts on it horizontally.
Why does the vertical component of a
projectile’s motion undergo change?
Because gravity is pulling it downward.
How does the vertical distance a projectile
falls below an otherwise straight-line path
compare with the vertical distance it would
fall from rest in the same time?
The vertical and horizontal distances are
equal.
A projectile is launched vertically at 100
m/s. If air resistance can be neglected, at
what speed does it return to its initial
level?
100 m/s
