Transcript Gravity, Air Resistence, Terminal Velocity, and Projectile

Gravity, Air Resistance, Terminal
Velocity, and Projectile Motion
Some basics…
Draw a picture along with each fact to help you remember it!
Won’t affect the
• An object’s mass _______
acceleration of the object due to gravity
on earth.
opposite
• Friction always acts in the _________
direction as motion.
surface area of an object will affect
• The ___________
the velocity of a free falling object
dropping towards earth.
What IS gravity?
• Gravity is NOT “the force that pulls you
down!”
• Gravity attracts all objects with mass inward
towards other objects with mass.
the Force of Gravity
What is the force of gravity?
The force of gravity is NOT the same as
the acceleration DUE to gravity!
Free Fall
Objects whose only acceleration is due to
gravity are in free fall.
Theoretically, objects in free fall continue
to accelerate as long as they are falling.
All free falling objects accelerate at the
same rate regardless of their mass. (9.8
m/s2)
 http://www.animations.physics.unsw.edu.au/mechanics/chapter2_projectiles.htm
l
• http://www.animations.physics.unsw.edu.au/
mechanics/chapter2_projectiles.html
Galileo's Famous Experiment
Acceleration of Gravity
 Any object which is being
acted upon only by the force
of gravity is said to be in a
state of free fall. There are
two important motion
characteristics which are true
of free-falling objects:
– Free-falling objects do not
encounter air resistance.
– All free-falling objects (on
Earth) accelerate downwards
at a rate of 9.8 m/s/s (often
approximated as 10 m/s/s)
• If the velocity and time for a free-falling object being dropped
from a position of rest were tabulated, then one would note
the following pattern. Acceleration is increased by 9.8 m/s
each second.
• Time (s)
Velocity (m/s)
• 0
0
• 1
- 9.8
• 2
- 19.6
• 3
- 29.4
• 4
- 39.2
• 5
- 49.0
Newton’s 2nd law states:
Forces cause
acceleration – force
times mass equal
acceleration.
The greater the mass
the smaller the
acceleration for a given
force.
http://www.pixton.com/
schools/gallery/n3bxfa4
u
Free Fall & Newton’s 2nd Law
•
Newton’s 2nd Law predicts this!
a=
F
m
• The force of gravity felt by a more
massive object is greater, thus the
greater the mass the slower/less
acceleration.
• The greater mass of the elephant (which
tends to produce small accelerations)
offsets the influence of the greater
force.
• The greater mass of the elephant
requires the greater force just to
maintain the same acceleration as the
feather.
•
http://www.physicsclassroom.com/Class/n
ewtlaws/u2l3e.cfm
W Richards Worthing High School
Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air
zero so he
resistance is _______
____ downwards.
accelerates
2) As his speed increases his air
increase
resistance will _______
3) Eventually the air resistance will be
big enough to _______
balance the
skydiver’s weight. At this point
the forces are balanced so his
constant - this is
speed becomes ________
called TERMINAL VELOCITY (no
acceleration/speed change)
How the forces change with time.
KEY
Gravity
(constant value &
always present…weight)
Air resistance
(friction)
Net force
(acceleration OR changing
velocity)
Projectile
Motion
p. 41
The curved path that an
object follows, launched,
or otherwise projected
near the surface of Earth.
Comparing a Vertical and
Horizontal Drop
• The red ball falls from rest, whereas the yellow ball is given a
horizontal velocity. Each picture in this sequence is taken after
the same time interval. Notice both balls are subjected to the
same downward acceleration since they remain at the same
elevation at any instant. Also, note that the horizontal
distance between successive photos of the yellow ball is
constant since the velocity in the horizontal direction is
constant.
Projectile Motion
 Projectile: When a
falling object also
experiences
horizontal motion
 Horizontal motion
does not affect
vertical motion
Circular Motion
• http://www.animations.physics.unsw.edu.au/
mechanics/chapter3_circularmotion.html