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
gravity.
Horizontal & Vertical Motion
• After the ball leaves from the force of the
pitcher’s hand, the ball’s horizontal velocity is
constant.
• The ball’s vertical velocity increases because
gravity causes it to accelerate downward.
• The two motions combine to form a curved
path.
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?
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
path.
• 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
travel.
Calculations
• 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
and
Vy = V0 * cos θ
Lab Conclusions:
What Really Happens?
• As the water balloon rises towards its peak, it undergoes a downward
acceleration.
• 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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