Transcript Unit 1 - Motion in a Straight Line

2.3 Projectile Motion
How would you describe the motion of an Olympic ski jumper as she begins her
jump off a ramp? The motion of a ski jumper is identical to that of a ball being
thrown forward in the air. Both travel through a two-dimensional curved path
called a parabola.
 A projectile is an object that moves along a
curved 2-D trajectory (path), under the
influence of gravity.
 The motion of a projectile under gravity is
called projectile motion.
What Will Happen?
Imagine you have two rubber balls, one in each
hand...a red ball and a yellow ball.
If you were to throw the yellow ball horizontally,
and simply drop the red ball, from the same
height, which ball would hit the ground first?
Both balls would hit the ground simultaneously!
(of course air resistance is negligible)
Why does this occur?
2.3 Projectile Motion
The white horizontal lines represent equal time
intervals between the camera’s flashing strobe.
Notice the vertical components of displacement
for both balls increase with time by the same
amount. Both balls experience the same vertical
motion.
As a result, both balls reach the ground at the
same time.
2.3 Projectile Motion
When analyzing projectile motion, the horizontal
motion (x-dir) and the vertical motion (y-dir) are
independent of one another.
The horizontal and vertical motions of a projectile
take the same amount of time.
Vertically, projectiles accelerate due to gravity. The
force of gravity acts downward.
Since no force is acting on a projectile horizontally,
it moves at a constant velocity in the x-direction.
Solving Projectile Motion Problems
Projectile motion problems are two-dimensional
vector problems. When analyzing these problems
it is important to separate x- & y-direction
variables.
Since the horizontal motion of a projectile
remains constant, we use the constant velocity
equation to solve for any unknowns in the
x-direction.
The horizontal distance (𝛥𝒅𝒙 ) covered by a
projectile is known as the range.
Solving Projectile Motion Problems
Vertically, the projectile accelerates due to
gravity, 𝒈 = 9.8 m/s2 [down].
In order to solve for any unknowns in the
y-direction, we can use the five uniform
acceleration equations to solve.
Although we analyze the x- & y- motions
independently, the one factor these motions
share in common is time (∆t).
SP # 1 p.77
2.3 Homework
Practice # 1,2 p.78
Questions #1,2,5,8* p.81