Transcript Projectile Motion

Physics Day 33
LO: recognize the independence of the horizontal
and vertical components of motion
AGENDA
Professional basketball player “Kiwi” has a
Do Now
hang time of 2.25 seconds with a 30 degree
launch angle.
Project
1) How long does it take to reach his
HW#6Pr. 1-3 maximum height?
2) What is the maximum height?
on page 99
3) Are these numbers reasonable?
What is a projectile?
• A projectile is any object that once projected or dropped
continues in motion by its own weight and is influenced
only by the downward force of gravity.
• a projectile is any object upon which the only force is
gravity.
•
Projectile Motion
• Describe the motion of an object in TWO
dimensions
• Keep it simple by considering motion close
to the surface of the earth for the time being
• Neglect air resistance to make it simpler
The Plane and The Package
In the course of its flight, the plane drops a package from its luggage
compartment. What will be the path of the package and where will it
be with respect to the plane?
Characteristics of a Projectile's Trajectory
• There are the two components of the projectile's
motion - horizontal and vertical motion.
• the projectile travels with a constant horizontal
velocity and a downward vertical acceleration.
• And since perpendicular components of motion
are independent of each other, these two
components of motion can (and must) be
discussed separately.
HorizontalMotion
VerticalMotion
•
•
•
•
•
•
Horizontal
Motion
Vertical
Motion
Forces
(Present? - Yes or No) (If present, what dir'n?)
•
•
No
Yes The force of gravity acts downward
•
•
Acceleration
(Present? - Yes or No) (If present, what dir'n?)
•
•
No
Yes "g" is downward at 9.8 m/s/s
•
•
•
•
Velocity
(Constant or Changing?)
Constant
Changing (by 9.8 m/s each second)
Where should the zookeeper aim her banana cannon
to successfully hit the monkey?
Projectile Motion
The ball is in free fall vertically and moves at
constant speed horizontally!!!
Projectile Motion
Examples
• A projectile is fired horizontally from a cliff44.1
meter high at an initial velocity of 50 m/s.
• 1) How long after it is fired does it hit the ground?
• 2) How far away from the cliff does it hit the
ground?
• 3) What it its vertical velocity as it hits the
ground?
Examples
• 2. Ima Peode wishes to throw a 2.8kg
pumpkin horizontally of the top of the
school roof (which is 10.4meter) in order to
hit Mr. K Who stands a distance of 13.4m
away from the base of the building. What is
the initial velocity must be in order to hit
Mr. K?
Projectile Motion
Projectile Motion
Projectile Motion
Projectile Motion
Projectile Motion
y
Horizontal (x)
dx  v x t
Vertical (y)
1 2
dy  v yi t  gt
2
v y  viy  gt
x
Projectile Motion
Satellites
• Curvature of the earth enters into our
calculations
If I start 5 m above the surface, it will still be at
5 m after one second if it is moving 8000 m/sec
Satellites
Throw at 8000 m/sec
This is about 18,000 mph
Earth circumference is
25,000 miles
Takes 25000/18000 = 1.4
hours = 84 minutes
Higher altitude longer
Satellites
Force of gravity on bowling ball is at 90o to
velocity, so it doesn’t change the velocity!!!
If no air resistance, gravity doesn’t change
speed of satellite, only direction!!!
Communications Satellites
• Farther out you go, the bigger the
circumference of the orbit
• It takes longer for the trip
• Also, gravity weakens by inverse square
law the farther out you go
• Make the distance so that it takes 24 hours
for the orbit
• Satellite is stationary in the sky!!!
Escape Speed
Throw at > 11.2
km/sec and ball
escapes the pull
of the earth!!!