Transcript projectile - Denton ISD

11-08-11
Agenda
Place on Your Desk:
*Calculator & Protractor
 1) Which instrument can we use in the
lab to measure force (Newton's)?
Spring scale
1) Warm-Up
2) Vocab.
5 min
Words
3) Projectile Motion
Intro.
4) Pre-Lab Vectors 15 min
5) Vector Lab 30 min
15 min
10 min
1. Projectile: an object that moves through the air space,
acted on only by gravity (and air resistance, if any)
2. Parabola: in projectile motion, it is the shape of the
path traced by a projectile.
3. Trajectory: the curved path taken by a projectile.
4. Horizontal distance: the distance a projectile moves
while falling; also called range.
5. Vertical component: vector which indicates the vertical
velocity of a projectile; initial force.
6. Horizontal component: vector which indicates the
horizontal velocity of a projectile; air resistance or
inertial motion.
Projectile Motion:
A projectile is any object that is projected by some
means and continues in motion by its own inertia.
Projectiles follow curved paths that have horizontal
and vertical components of motion. Horizontal
component of motion is completely independent of
the vertical component of motion. Their combined
effects produce the variety of curved paths that
projectiles follows.
We find that projectiles move equal horizontal
distances in equal time intervals since no acceleration
takes place horizontally. The only acceleration is
vertically in the direction of the earths gravity. The
vertical component also changes and the horizontal
component stays the same.
Move equal horizontal distances in equal
time intervals.
The path traced by a projectile that accelerates only in
the vertical direction while moving at constant
horizontal velocity is called a parabola. When air
resistance can be neglected, the curved paths are
parabolic and the paths are called trajectories.
DUE TODAY:
• Projectile fill-in-blanks (KEEP)
• Vector Lab
“Wisdom begins in wonder.”
Socrates
DUE NEXT CLASS:
• Finish Vector Lab questions & abstract
• Bring Calculator & Protractor!
Projectile Motion
Projectile – any object that
is projected by some
means and continues in
motion by its own inertia
EX: a cannonball shot from a
cannon
a stone thrown in the air
a ball rolling off the table
Gravity acts DOWNWARD
So, a ball moving horizontally has NO GRAVITY
affecting its velocity.
So, the only horizontal component is due to the
initial force applied—NO acceleration is found in
the horizontal axis.



The horizontal direction is the x axis.
Ignoring drag, there is no force acting on
the projectile horizontally.
What keeps the object in MOTION is:
Inertia which is present-1st Law of
Newton is being followed.
If the object slows down or stops—it is due
to FRICTION.
If that ball is dropped,
suddenly gravity acts on it
to pull it down.
Now it has a
vertical component.
g
is constant in magnitude,
always in the straight down
direction, and always along
the y axis; if air resistance is
neglected; then, the motion
of the center of mass is only
due to the force of gravity
accelerating or decelerating
the mass.
 Projectile
motion under the
influence of near-Earth--gravity will produce a curved
path.
 The vertical direction is on
the
“y “axis. The only force
acting on any projectile
vertically will be gravity. The
acceleration will be the
constant g = 9.806 65 m/s2.
 KEY:
What happens to a
particle vertically does not
affect its horizontal motion.
The opposite is also true.
The axes are independent.
 NOTE
what axis is CHANGING!!
Figure 6-15(Hewitt book)
If a projectile had no gravity, it
would move with this path:
Gravity pulls the projectile
towards the Earth.
Those projectiles that
accelerate only in a vertical
direction while moving at a
constant horizontal velocity
have a path that forms a
PARABOLA.
Air resistance is another force
that acts on projectiles.
It changes the path of a
projectile like this:
IDEAL PATH
ACTUAL PATH
If air resistance is
negligible, a projectile
will rise to its maximum
height in the same
amount of time it takes it
to fall back down.
Without air resistance,
the deceleration of the
projectile going up is
equal to the acceleration
of the projectile coming
back down.
 The
range is the horizontal
distance.
 Solve for the time needed for the
projectile to reach its maximum
height
(remember that gravity is acting)
by using the “vertical” distance.
 Once you know the time of flight,
solve for the range by using:
DH = Horizontal velocity X
Time
 Satellite
– an object that
falls around Earth or some
other body rather than
falling into it because of its
tremendous speed.
◦Page 127 (Hewitt book)

If no force acts horizontally, the motion
found is at constant velocity- due to
inertia.
 The
equation of motion is then DH =
VH t.
 BUT, to find VH when you have 2dimensional motion, resolve the
initial velocity into its horizontal
component by using the formula :
VH = Vi cos q.
 To
find Vv , resolve the
initial velocity into its
vertical component.
 The formula to do this is:
Vv = Vi sin Ø
 The
time an object
moves horizontally is
the same as the time
the object moves
vertically.
 So, Total time is the
“time in the air” for a
projectile at-an-angle.
To find time:
Remember that gravity is affecting the motion
and therefore, the amount of time the
projectile is in the air for “at an angle” will be
TOTAL time.
 So,
ttotal = Vv / g so DH = VH ( t t)

A vertical and a horizontal
component. With the trajectory
being the initial velocity*
 Acceleration
is constant for a
projectile.
 Speed and velocity change at
each point along the
parabolic pathway.
 What is the speed of the
projectile at the very top of
its pathway?
 What is the acceleration of
the projectile at the very top
of its pathway?