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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
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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 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).
Terminal Velocity The constant velocity of a falling object when the force of air resistance equals the force of gravity.
Free Fall • The motion of an object when only the force of gravity is acting on the object. (NO air resistance)
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.