Freefall Motion Notes

Any object near the surface of the Earth experiences the pull of gravity.

If released from rest, the object will fall freely toward the planet.

Freefall

As they fall, the vertical velocity increases every second.

The vertical velocity increases by 9.8 m/s every second.

This is the Acceleration due to gravity

g = - 9.8 m/s/s

For our class we will use - 10 m/s/s

Falling objects

y = vit + gt2 Gives the position

2

When vi = 0 then position = gt2

2

vf = vi + gt , for dropped objects vf = gt

Problem

A flowerpot falls off a second-story window. It starts from “rest” and hits the sidewalk 1.5 s later with a velocity of -14.7 m/s.

What is the average acceleration?

a = (vf – vi) /t

(-14.7 m/s – 0m/s)/1.5 s = -9.8 m/s2

Freefall

For an object thrown straight up into the air, it experiences a downward acceleration of g = - 10m/s/s

Any object that is moving vertically and acted on by only gravity is in freefall.

This is regardless of initial motion. The acceleration is constant regardless of motion.

Freefall

Objects thrown upward slow down until gravity brings them to a stop.

At the top, velocity is zero but there is still gravity and an acceleration downward.

So g = -10m/s/s

Freefall

A ball is thrown upward at 30 m/s, How long till it reaches the top of its travel?The ball will stop moving at the top and

have zero velocity so…… t=(vf – vi)/g

t=(0m/s – 30m/s)/-10m/s/s = 3 sWhen the ball falls back down to the height it

started from, it will have the same speed but be traveling downward.

Freefall

A ball is thrown upward at 30 m/s, How fast will it be going when it falls back to the same height it started from? The ball will stop moving at the top and

have zero velocity, and it takes twice as long to make a round trip as one way so …

vf = vi +gt

vf = 30 m/s + (-10m/s/s)(6s)= -30m/s

Terminal velocity

In the real world, air resistance will result in the object reaching a maximum speedTerminal Velocity – max speed reached due

to air resistance.All objects reach this speed when falling in

the real world. It is dependent on how aerodynamic the object is.

REVIEW

Why do all objects fall?GravityWhat is the acceleration due to gravity?g = -10 m/s/sIf a ball is thrown straight upward, how

fast will it be going at the maximum height?

0 m/s