Please sit at the seats you were at Friday…

Get out paper and something to write with!

On a sheet of paper answer the following questions…you may ask a neighbor.

1. What is gravity?2. What is the value of acceleration due to gravity? (**Hint: You’ve seen this number in science class before!)

3. What happens to the speed of an object as it moves upwards? Downwards?

4. What is the difference between speed and velocity?

Gravity and Free Fall

Gravity and Free Fall

What would happen if you dropped a baseball

out a second-floor window?

Gravity and Free Fall

Describe the speed of the baseball, at the beginning when you let it go, and at the end when it hits the

ground

Gravity and Free Fall

Is the speed of the baseball constant or does

it accelerate?If it accelerates, at what

rate?Do ALL objects fall at the

same rate?

Gravity and Free Fall

Free fall – an object is in free fall if it is accelerating due to the force of gravity and NO other forces are acting on it* a ball thrown upward is also in free fall after it leaves your hand

Gravityhttp://

www.youtube.com/watch?v=PsIBz40PcQ8

Gravity and Free Fall

Acceleration due to gravity – Objects on Earth accelerate downward at 9.8 m/s2

In physics, this value is represented by the letter g

Gravity and Free Fall

Acceleration due to gravity

g = 9.8 m/s2

Gravity and Free Fall

What does an acceleration of 9.8m/s2 really mean?

What is happening to the speed?

Gravity and Free FallUpward Launches

When an object is in free fall, it accelerates downward at 9.8 m/s2. • Gravity causes the

acceleration by exerting a downward force.

So what happens if you throw a ball upward?

Gravity and Free FallThe ball will slow down as

it moves upward, come to a stop for an instant, and

then fall back down

Gravity and Free Fall As it moves upward, the speed decreases by 9.8 m/sec every second until it reaches zero. The ball thenreverses direction and starts falling down. As it falls downward, the speed increases by 9.8 m/sec every second.

Gravity and Free FallIn this picture, the ball’s initial velocity is +19.6 m/sec and its velocity four seconds later is -19.6 m/sec.

How come?

Gravity and Free FallWhat is the ball’s speedafter 2 seconds, at the top?

What is the ball’s acceleration after 2Seconds at the top?

Gravity and Free Fall

A ball is thrown straight up into the air. As it moves upward, its speed _________ by _____ each second. As it falls back down, its speed ________ by____ each second.

decreases 9.8

increases 9.8

Gravity and Free Fall

What is the difference between speed and

velocity?

Gravity and Free FallNow let’s do some

calculations!

Gravity and Free Fall

The rate of acceleration due to gravity, 9.8m/s2 is the same for all objects, and is always 9.8m/s2 on

the Earth’s surface.So…

Gravity and Free FallUsing this formula, the height an object falls

(displacement), or the time it is in free fall can be

calculated if one of those variables is given

Gravity and Free Fall

Gravity and Free Fall• If you are given the time

an object is in free fall, you can calculate how far it fell

OR• If you are given the

height it fell, then you can calculate the time it took to fall

Gravity and Free Fall

Gravity and Free Fall

Let’s make this formula easier to use if a free falling object starts at

rest.

Gravity and Free FallYou drop a ball from the edge of a cliff. It lands 4 seconds later.What distance does the ball fall during the 4 seconds?

Gravity and Free FallA stone tumbles into a mine shaft and strikes bottom after falling for 47.3 seconds. How deep is the mineshaft?

Gravity and Free FallThe climber dropped her compass at the end of her 240-meter climb. How long did it take to strike bottom?

What if you are only given a speed…How do you calculate displacement?

What equation have we already used that involves speed/velocity and acceleration?

Gravity and Free FallAt a construction site a pipe wrench strikes the ground with a speed of 24 m/s. Calculate the height the pipe wrench was inadvertently dropped.

Wrap-Up ReviewGravity/Free Fall

What is an example?Acceleration due to gravityUpward launch

What is an example?Velocity vs. SpeedFormula