Free Fall and Terminal Velocity

CH4Physics A

Winter, 2010-2011

Acceleration of Gravity, Free Fall, and Projectile Motion

Acceleration of Gravity• The acceleration of gravity near the earth’s

surface is 9.8 m/s2 for ALL objects.

• This means that objects will accelerate at a rate of 9.8 m/s every second when in free fall.

• Equation– V = g x t

Galileo dropped a cannon ball and musket shell and found they landed at the same time

Example ProblemExample Problem: If an object is dropped from a building, how fast will it be going if it falls for 4 seconds?

V = g x tV = (9.8 m/s2) x (4 seconds) = 39.2 m/s (which is about 100 mph)

Example #2• You want to know how high above the ground you are, so you drop

a rock off a tall bridge.• Distance = ½gt2

• You count and see it takes 7.3 seconds to hit the river.

Example #2• You want to know how high above the ground you are, so you drop

a rock off a tall bridge.• Distance = ½gt2

• You count and see it takes 7.3 seconds to hit the river.• Thus d = ½ * (9.8 m/sec2) * (7.3sec)2

• D = 267 meters or 876 feet tall

Free Fall• Free Fall

– When something falls through the air it is experiencing free fall

(meaning it accelerates at a rate of 9.8m/s2).

• Terminal Velocity– The velocity reached when the force of friction

(air resistance) becomes equal to the force of gravity pulling down.

– Diagram

The force of air resistance going up equals the force of gravity going down

Fair

F gravity

102,000 feet

614 mph

Terminal velocity helps flying squirrels jump from tree to tree

Terminal Velocity• Two primary factors affect Terminal

Velocity.

• Area (how much air is caught under it)

• Mass (how much air can be pushed out of the way).

• Heavier objects increase TV while wider objects decrease it.

Terminal Velocities Compared134 mph

20 mph

200 mph

204 mph 74 mph

20 mph2 mph