Free Fall

Free Fall

Open Ended

Journal - Before their parachutes open, skydivers sometimes join hands to form a ring as they fall toward Earth. What happens if the skydivers have different masses? Do they fall at the same or different rates?

Galileo's Discovery

Which falls with more acceleration, a piece of paper or a physics book?

Poll

Ok, they both fall at the same speed, so what exactly is free fall

• When any object is falling

• When gravity is the only significant force acting on the object

• When an object falls and gravity and air resitance work together to maintain its speed

Galileo

About 400 years ago, Galileo Galilei discovered that, neglecting the effect of air, all objects in free fall have the same acceleration.

Galileo

It doesn't matter what they are made of or how much they weigh.

David Scott

David Scott dropped both a hammer and a feather on the surface of the moon (1/6 the gravity of earth). What happened?

Free-fall acceleration on earth

• 9.8 m/s² (about) downward

• 22 mph/s downward.

What does that mean?

Each second a skydiver falls, his downward velocity increases by 9.8 m/s,

Positive or Negative acceleration

• Depends upon the coordinate system you use.

• If you define positive as upward, the free-fall acceleration is negative.

• If you describe positive as downward, the free-fall acceleration is positive

Poll

Is the ball rising or falling? The time interval between each photo is 0.06s.

• Rising

• Falling

Trick question

It could be either!

If it's downward

We know that the time intervals are equal and the distance between the ball in each image increases, therefore we know that the speed is increasing. If the upward direction is positive, then the velocity is becoming more and more negative

If it is upward

For a standard, let's say the ball is thrown upward with a speed of 20.0 m/s. If upward is chosen to be positive, then the ball starts at the bottom of the image with a positive velocity; therefore, the acceleration would be -9.8 m/s². Because velcotiy and acceleration are in opposite directions the speed of the ball decreases.

What does this mean?

Since the ball started upward with an initial velocity of 20 m/s, and the acceleration is -9.8m/s², after 1 second, it's velocity would be 20 - 9.8 or 10.2 m/s.

Open Ended

Exit Ticket - How does in an object in space stay in orbit?