Gravity & Free Fall

Elephant vs. Feather

•If both are dropped from the same height at the same time, which will hit the ground first?

•On Earth?

•On the moon?

Freefall• Movement of an object towards

earth solely because of gravity

– Gravity acts downwards towards center of earth

• Acceleration due to gravity for any falling object = g

g= 9.8 m/s2

What “g” means

• Any object in free fall will increase its speed/velocity by 9.8 m/s each second.

• g (9.8 m/s2) stays constant for the duration of free fall

Ball in free fallTime = 0 sv = 0

Time = 1 sv = 9.8 m/s

Time = 2 sv = 19.6 m/s

Time = 3 sv= 29.4 m/s

The change in ball’s speedis always 9.8 m/s2

ball is covering more distance the longer it falls

Viewing Free Fall

• Free Fall applet

Air Resistance

• Present on earth

• acts in opposite direction of gravity– (reduces

acceleration)

Falling Ball

Gravityg=9.8m/s2

Air resistance

Air Resistance• If objects fall for long period of time:

• Force of Air resistance = force of gravity – Forces balanced

– Object falls at constant speed called terminal velocity

Terminal Velocity

• Air resistance increases with:

• 1. Increasing Speed

• 2. Increasing surface area Parachutes slow

downward acceleration

Viewing Terminal Velocity

Elephant vs. Feather• Without air resistance (outer

space)• Free falling objects

• Both hit at same time

Elephant vs. Feather• With air resistance (earth)

• With air resistance

• Elephant hits first