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Projectile Motion February 4, 2013

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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.

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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.

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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.

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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 6 th person can split responsibilities with Distance Recorder

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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 3 rd 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 2 nd Law).

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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 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 v x is the initial velocity in the x or horizontal direction and v y 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.

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Calculations Once can calculate the initial velocity of the water balloon using: To calculate the initial horizontal velocity and vertical velocity using V x = V 0 * cos θand V y = V 0 * cos θ

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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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