Transcript Gravity2 - isd194 cms .demo. ties .k12. mn .us

Gravity Part 2
Review
• Acceleration: the rate at
which velocity changes
• Acceleration rate of gravity:
9.8 m/s/s
How fast does an object
accelerate as it falls?
9.8 m/s
19.6 m/s
Quic k Ti me™ and a
T IFF (Unc om pres s ed) dec om pres s or
are needed to s ee t his pic t ure.
29.4 m/s
39.2 m/s
Change in velocity = gravity x time
• A penny at rest is dropped from
the top of a tall stairwell. What
is the penny’s velocity after it
has fallen for 2 seconds?
Gravity = 9.8 m/s/s
Iime = 2 seconds
9.8 m/s/s x 2 s = 19.6 m/s
Another Practice Problem
• The same penny from above hits
the ground in 4.5 seconds. What
is the velocity of the penny right
before it hits the ground?
Gravity = 9.8 m/s/s
Time = 4.5 seconds
9.8 m/s/s x 4.5 s = 44.1 m/s
Time = change in velocity/gravity
• A marble at rest is dropped from
a tall building. The marble hits
the ground with a velocity of 98
m/s. How long was marble in the
air?
Change in velocity = 98 m/s
(final velocity - starting velocity)
Gravity = 9.8 m/s/s
98/9.8 = 10 seconds
Another Practice Problem
• An acorn at rest falls from an
oak tree. The acorn hits the
ground with a velocity of 14.7
m/s. How long did it take for the
acorn to land?
• Change in velocity = 14.7 m/s
(14.7 - 0 = 14.7)
Gravity = 9.8 m/s/s
14.7/9.8 = 1.5 s
Air Resistance
• The force that opposes the
motion of objects through
the air (goes against
gravity).
QuickTi me™ and a
T IFF (Uncom pressed) decom pressor
are needed to see t his pict ure.
Terminal Velocity
The constant velocity of a falling object
when the force of air resistance
equals the force of gravity.
QuickTime™ and a
TIF F (Uncompressed) decompressor
are needed to see this picture.
Free Fall
• The motion of an object when
only the force of gravity is
acting on the object. (NO air
resistance)
QuickTi me™ and a
TIFF ( Uncompressed) decompressor
are needed to see thi s pi ctur e.
DID YOU KNOW?
Where are the two places where free
fall occur? SPACE and SCIENTIFIC
VACUUM
Orbiting occurs because of two separate
forces acting on the object, for
example a spacecraft. The two forces
are GRAVITY and FORWARD
THRUSTERS.
Centripetal means TOWARD THE
CENTER. Centripetal forces cause
objects to travel in a CIRCULAR path.
Projectile Motion
• The curved path that an
object follows when thrown
near the Earth’s surface.
Qui ckTime™ and a
TIFF (U ncompr essed) decompressor
are needed to see thi s pi cture.