Freefall

Acceleration Due to Gravity Galileo did many experiments and proved that if you ignore air resistance: All objects fall to the earth with uniform acceleration. Mass of the object does not matter. Distance above the ground does not matter. Objects accelerate at 9.81 m/s2 or 32.2 ft/s2. This varies slightly because of the distance between the object and the center of the earth.

Uniform Acceleration

Objects dropped will speed up. Objects thrown up will slow down. Gravity causes objects to accelerate downward. Gravity is the attractive force between two objects. When objects are falling, the only force on them is gravity, and they are in freefall. Objects in freefall feel “weightless” because the only force is gravity.

Ground level is the reference. Frame of Reference Ground level is the reference. going up : +y, +v a = -g = -9.81 m/s2 Slowing Down ground level going down : -y, -v a = -g = -9.81 m/s2 Speeding Up

Acceleration due to gravity : -g = -9.81 m/s2 Use a = -g = -9.81 m/s2 any time an object is moving up or down! Assume NO air resistance! efff.gif

y = 0 +va Maximum Height Velocity = 0 time = ½ total time At same height object thrown same velocity, opposite direction y = 0, -va Ground Level

Reference is the ground. Direction Motion Position Velocity Acceleration Up Slowing Down +x +v - g Apex Stop +x - g Down Speeding Up +x - v - g Down over the Cliff Speeding Up - x - v - g

vavg = ½(v + v0) y = ½(v + v0)t v = v0 + (-g)t y = v0t + ½(-g)t2 Use the same formulas except use a = -g = -9.81m/s2 vavg = ½(v + v0) y = ½(v + v0)t v = v0 + (-g)t y = v0t + ½(-g)t2 v2 = v02 + 2(-g)y

Example Problems Homework – Freefall!