Transcript Projectile Motion




Any object that moves through the air or
through space, acted on only by gravity
A projectile is any object which once
projected continues in motion by its own
inertia and is influenced only by the
downward force of gravity.
Examples – a stone thrown into the air, a ball
rolling off a cliff, a cannonball shot from a
cannon.
1. Horizontal Component of Motion –
similar to a ball rolling freely along a
level surface; when friction is
negligible, a rolling ball will move at
a constant velocity (equal intervals of
time).
2. If there is no horizontal force acting
on the object, there is no horizontal
acceleration.

2. Vertical Component of Motion –
similar to a freely falling object –
acceleration due to
____________???. As the ball
falls, the increasing speed causes a
greater distance to be covered
each second.
**The ball follows a “parabolic” path.**



The horizontal and vertical velocity
components of vectors are independent of each
other (have no affect) .
But… the combined effects of each component
produce the curved paths that projectiles
follow.
What do you call the sum or product of two
projectile vectors?

Suppose the zookeeper must shoot the banana from the
banana cannon to the monkey who hangs from the limb
of a tree. This particular monkey has a habit of dropping
from the tree the moment that the banana leaves the
muzzle of the cannon. The zookeeper is faced with the
dilemma of where to aim the banana cannon in order to
hit the monkey. If the monkey lets go of the tree the
moment that the banana is fired, then where should she
aim the banana cannon? To ponder this question, first
consider a scenario in which there is no gravity acting on
either the banana or the monkey. What would be the
path of the banana? Would the banana hit the monkey?

If the monkey lets go of the tree the moment
that the banana is fired, then where should she
aim the banana cannon? To ponder this
question, consider the scenario in which the
zookeeper aims above the monkey (perhaps
she presumes that gravity will accelerate the
banana downward such that it hits the
monkey). What would be the path of the
banana? Would the banana hit the monkey?

To ponder this question, consider the scenario
in which the zookeeper aims at the monkey
and shoots the banana very fast (perhaps she
presumes that if shot fast enough, the banana
will hit the monkey before it falls very far).
What would be the path of the banana? Would
the banana hit the monkey?

If the monkey lets go of the tree the moment
that the banana is fired, then where should she
aim the banana cannon? To ponder this
question, consider the scenario in which the
zookeeper aims at the monkey, yet shoots the
banana very slow. What would be the path of
the banana? Would the banana hit the monkey?



A projectile is an object upon which the only
force is gravity. Gravity acts to influence the
vertical motion of the projectile, thus causing
a vertical acceleration.
The horizontal motion of the projectile is the
result of the tendency of any object in motion
to remain in motion at constant velocity. Due
to the absence of horizontal forces, a
projectile remains in motion with a constant
horizontal velocity; horizontal forces are not
required to keep a projectile moving
horizontally.
The only force acting upon a projectile is
gravity!



Imagine a pickup truck moving with a
constant speed along a city street.
In the course of its motion, a ball is projected
straight upwards by a launcher located in
the bed of the truck.
What will be the path of the ball and where
will it be located with respect to the pickup
truck?
1.
4.
As can be seen from the above animation, the ball follows a parabolic path and remains directly above the
launcher at all times.
2.
As the ball rises towards its peak, it undergoes a downward acceleration.
a)
An upwardly moving ball which is slowing down is said to be undergoing a downward acceleration.
3.
As the ball falls, it also undergoes a downward acceleration.
a)
A downwardly moving ball which is gaining speed is said to have a downward acceleration.
b)
This downward acceleration is attributed to the downward force of gravity which acts upon the ball.
If the ball's motion can be approximated as projectile motion (that is, if the influence of air resistance can be
assumed negligible), then there will be no horizontal acceleration.
5.
In the absence of horizontal forces, there would be a constant velocity in the horizontal direction.
6.
This explains why the ball would be located directly above the launcher from which it is projected.
7.
Many would insist that there is a horizontal force acting upon the ball since it has a horizontal motion.
a)
This is simply not the case.
b)
The horizontal motion of the ball is the result of its own inertia.
c)
When projected from the truck, the ball already possessed a horizontal motion, and therefore will
maintain this state of horizontal motion unless acted upon by a horizontal force.
12. A plane is flying at an altitude of 8000 m at
a sped of 250 m/s. At what horizontal
distance ahead of its target must a water
balloon be released to strike the target on
the ground(neglecting air resistance)?