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? • 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 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.