Falling objects

1
Falling objects

• All falling objects accelerate on the way down.
• On Earth they accelerate at 9.8 m/s/s.
• That means that the falling object speeds up on
  the way down.
• It goes 9.8 m/s faster every second.
• This is a constant we can use to find other
  pieces of information because ALL objects on
  Earth accelerate at the SAME rate9.8 m/s/s.
• Whether is is a gold ball or a bowling ball
  everything falls at 9.8 m/s/s.

2
Soany two objects

• Galileo taught us this through experimentation
• Any two objects dropped from the same height at
  the same time will hit the ground at the same
  time. All objects accelerate 9.8 m/s/s so a golf
  ball and a bowling ball dropped from our room
  window will hit the ground at the same time.

3
A couple of useful equations

• We can find distance traveled
• Distance equals velocity initial plus one half
  acceleration times time squared.
• And another useful equation
• Velocity final squared is equal velocity initial
  plus 2 times acceleration times distance.
• These are often used when we know acceleration
  and want to know distances.

4
How long do falling objects accelerate?

• It turns out that here on earth falling objects
  may stop accelerating as they fall through air.
• Remember air is MATTER it is made of atoms it is
  a fluid that produces friction with any object
  moving through it.
• So when an object falls, lets say dropped from
  an airplane, it accelerates for a time until the
  pull of gravity, the force causing it to fall, to
  accelerate downward, is BALANCED by the upward
  force of air frictionor air resistance.
• When gravity down is eaula to air resistance up
  then the forces are balanced and so the object
  will????

5
STOP ACCELERATING

• Remember that when forces are balanced, that is
  they are equal and opposite, the object does not
  accelerate. It moves at some constant velocity.
  For falling objects that is called the terminal
  velocity. Its ABOUT 120 -125 miles / H.
• When it reaches that speed it stops accelerating.
  It comes to some velocity and just stays at that
  speed and in that directionconstant velocity.

6
PROJECTILES

• A projectile is any object thrown through the air
  without any engine so that as it moves, the only
  force acting on it is gravity and air resistance.
• A projectile could be a thrown ball, arrow,
  missile, spitball.
• The path of all projectiles is a parabolic
  curvea curved path.
• Once released, gravity is acting vertically
  pulling it down at the same time it is moving
  horizontally downrange.
• What is true about projectiles is
• 1. Velocity in the horizontal direction remains
  constant if we ignore air resistance which we
  will do
• 2. In the vertical direction the object is
  accelerating downward at 9.8 m/s/s.
• 3. At the top of the run, the peak, the highest
  point vertically the velocity in the vertical
  direction is zerothough it continues to
  accelerate at 9.8 m/s/s
• 4. As we throw something up in the air, the
  object slows down as it rises to its maximum
  height. It slows down at the rate of 9.8 m/s
  slower every second it rises..
• It rises until its vertical up velocity is
  zero..
• 5.Then it starts to fall down and it speeds up at
  9.8 m/s/s
• 6. All the while this is going on, it continues
  to move horizontally at constant speed.
• 7. The launch angle will determine how high it
  will travel and how far downrange it will go.

7
DESIGN AN EXPERIMENT

• DESIGN AN EXPERIMENT WHICH LAUNCHES A PROJECTILE
  AT DIFFERENT LAUNCH ANGLES
• Write a detailed report including materials,
  process, outcome, conclusion. Be sure to figure
  out ways to QUANTIFY all of this. That is the
  difficulty of this lab.
• 10 points
• Due_____________________