Projectile Motion & Water Balloon Slingshot Activity Notes_February

Projectile Motion
February 4, 2013
Projectiles & Motion
• Projectile: an object thrown, kicked, hit, or
launched through the air.
• Projectile Motion: motion of airborne stuff (Ex: a
punted football, a bullet shot from a gun, a
pitched baseball).
• How can certain variables influence the range of
a projectile?
– Angle, initial velocity, air resistance, mass, shape, and
Horizontal & Vertical Motion
• After the ball leaves from the force of the
pitcher’s hand, the ball’s horizontal velocity is
• The ball’s vertical velocity increases because
gravity causes it to accelerate downward.
• The two motions combine to form a curved
Water Balloon Slingshot Activity
• Tomorrow we are going to work with
projectile motion; specifically a projectile’s
parabolic arc.
• Break down into groups of 5-6 students.
Water Balloon Activity Jobs
• Balloon Launcher: Gets the mass of five balloons and carries in
plastic bag; Loads balloon and fires.
• Horsemen: (2-students): Hold Sling-shot on both ends; Should be
equal in height
• Distance Recorder: Sights in the angle; places popsicle stick at
center of impact area; measures the distance from launch position
to impact when three trials are complete
• Time Keeper: Records the time it takes the balloon from launch
position to impact area
• *If there is six students to a group than the 6th person can split
responsibilities with Distance Recorder
Space Exploration & Military Use
• A rocket can rise into the air because the gases it
expels with a downward action force exert an
equal but opposite reaction force on the rocket
(Newton’s 3rd Law).
• The Army uses howitzers and mortars to send
explosive projectiles into enemy territory.
• Artillery personnel determine the distance of the
target and adjust the angle of the gun according
to the known initial velocity of the projectile.
• Artillery personnel can adjust the velocity of the
ordinance increasing the amount of force
(impulse). (Newton’s 2nd Law).
What Determines the Distance the
Projectile Will Travel?
• Artillery equations start with the initial velocity of the
projectile, which can be divided into its vertical and
horizontal components.
• If a projectile is launched as some angle, it will start with
both vertical and horizontal velocity, following a parabolic
• Projectile leaves cannon at angle θ with the ground.
• The initial velocity of the projectile can be separated into its
x and y components, where vx is the initial velocity in the x
or horizontal direction and vy is the initial velocity in the y
or vertical direction.
• It leaves the cannon at a height h from the ground.
• These variables determine the distance the projectile will
• Once can calculate the initial velocity of the water
balloon using:
• To calculate the initial horizontal velocity and
vertical velocity using
Vx = V0 * cos θ
Vy = V0 * cos θ
Lab Conclusions:
What Really Happens?
• As the water balloon rises towards its peak, it undergoes a downward
• An upwardly moving water balloon which is slowing down is said to be
undergoing a downward acceleration.
• As the water balloon falls, it still undergoes a downward acceleration.
• A downward moving water balloon which is gaining speed is said to have a
downward acceleration.
• The downward acceleration is depicted by a change in the vertical
component of velocity.
• This downward acceleration is caused by the downward force of gravity
which acts upon the water balloon.
• The horizontal motion of the water balloon is the result of its own inertia.
• When launched from the sling-shot, the water balloon already possessed
a horizontal motion.
• The water balloon will maintain this state of horizontal motion unless
acted upon by a horizontal force.

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