Projectiles

Bellwork Complete Wednesday and Thursday’s bell work Do not play with materials in basket

To do: Place the images into 2 categories Projectile Motion Non-Projectile Motion

A Projectile is . . . An object thrown or launched into the air that is subject only to gravity

Projectiles include: Throwing a baseball shooting an arrow hitting golf balls long jumpers

To do: Using the materials in your basket, build an apparatus that will launch the marshmallow with a parabolic trajectory Think about: How does the velocity of the marshmallow change as it travels through the air? Is there a difference between the velocity in the x direction and the velocity in the y direction? What is the only force acting on the cotton ball once it has been launched? How can you make the cotton ball go higher? Further?

Bellwork 1. What is the acceleration of a tossed ball at the top of its path? 2. How do you find the displacement of an object from a velocity time graph? 3. Draw a position time graph that shows Object traveling with constant velocity Object decelerating Object at rest

Projectile motion Has both a horizontal and vertical component (part) These components are independent of one another http://www.physicsclassroom.com/shwave/projectile.cfm

Trajectory The path of a projectile is called a trajectory the shape of a projectile’s path is a parabola

Horizontal motion A projectile moves forward due to INERTIA Inertia is the reluctance of an object to change its motion

Horizontal motion A projectile continues forward at constant speed because no HORIZONTAL FORCE acts on it The velocity in the horizontal direction remains the same throughout flight

Vertical motion Gravity pulls on any object and causes it to return to earth This means that the vertical velocity changes This motion is just like an object in free fall

Projectiles launched horizontally Half picture projectiles

Projectile Velocity Separate the motion into x and y components (parts) When an object is launched horizontally, the VERTICAL velocity is 0 m/s

Vx Actual path vy

The acceleration of the object in the y direction is due to gravity (like free fall) Use kinematic equations to solve for unknowns in both the x and y directions

Mythbusters http://www.youtube.com/watch?v=abUBrQmI33Q

Useful Distance Equations For horizontal distance: OR This equation for average velocity can also be used for finding velocity in the horizontal (x) direction.

Useful Distance Equations For Vertical Distance

Useful Velocity Equations For vertical velocity

Useful Velocity Equations Remember that horizontal velocity remains the same throughout flight

Time of flight The time of flight can be determined using kinematic equations used for free fall. Remember, the only force acting on an object once it has been launched is gravity.

Example: A stone is thrown horizontally at 15 m/s from the top of a cliff 44m high. A. How long does the stone take to reach the bottom of the cliff? B. How far from the base of the cliff does the stone strike the ground?

Time Solution

Distance Solution

Given Information v = 15 m/s vi = 0 m/s d=? d = 44 m, down Horizontal Values Vertical Values v = 15 m/s vi = 0 m/s d=? d = 44 m, down Constant speed a = -9.8 m/s2 t=

Time Solution -44m = 1/2(-9.8m/s2)t2 t = 3 s

Distance solution: d = vt d = 15 m/s x 3.0 s d = 45 m

Upwardly Launched Projectiles (at an angle) The result of simultaneous horizontal and vertical motion is a curved path