Physics Lab

1
Physics Lab

• Agenda Thursday 12/16/04
• Pick-up materials on front desks
• Intro to Horizontal Motion Lab
• Bring physics HW to do in class

2
Physics

• Agenda Thursday 12/16/04
• Return Plane Labs
• Horizontal Motion
• HW Read p. 155-157 and probs. p. 170 8, 9, 22

3
Projectile Motion

• A projectile can be anything that moves though
  the air after it has been given an initial
  thrust or input force
• Projectiles are only under one force as they move
  through the air GRAVITY!
• We ignore air resistance in most cases to simply
  the problems
• There are two general categories
• Projectiles launched horizontally
• Projectiles launched at an angle

4
Projectile Motion

• Bullet Demonstration
• Ballistics Cart Demo

• Important Concepts
• Vertical and horizontal motions are
  independent of each other
• We can relate the height, time in the air, and
  initial vertical velocity of the projectile by
  using its vertical motion, then determine the
  range (x-distance)
• We use basic motion equations to solve!

5
What do You Notice??
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Projectiles Launched Horizontally

• A cat is tossed horizontally at 20 m/s
• off a cliff that is 50 m high.
• How long is the cat in the air?
• b) How far from the base of the cliff
• does the cat land?
• How fast is the cat moving the
• Instant before it splats on the ground?

7
Problems Solving Strategy

• 1. Write known and unknown variables
• 2. Write variables for x and y directions

Whats missing?
vyf ?
ay g -9.8m/s2
yi 0
vyi 0
ax 0
vxi 20 m/s
WHY?
vxf 20 m/s
vnetf ?
yf -50 m
t ?
xf ?
xi 0
8
Practice Problem 2

• A plane that is moving 200 m/s drops a package.
  The package takes 15 seconds to reach the ground.
• A) What height was the package dropped from?
• B) How far did the plane travel from the time the
  package was released until the package hit the
  ground? Is this the same distance the package
  travels?
• C) How fast was the package moving when it hit
  the
• ground?

End
9
Regents Physics

• Agenda
• Projectile Motion
• Projectiles at any angle
• HW problems p. 160 12,13
• problems p. 172 42, 47 (tricky)

10
Review Problem

• A plane that is moving 225 m/s drops a package.
  The package takes 10 seconds to reach the ground.
• A) What height was the package dropped from?
• B) What horizontal distance did the package cover
  after it was dropped from the plane?
• C) How fast was the package moving when it hit
  the
• ground?

11
Projectiles at Any Angle..a few differences

• When projectiles are launched at any angle, the
  initial velocity has both horizontal and vertical
  components
• This means that Vo must be used, not just Vxi
  weve done this before!

Vxi Vocos ?
Vyi Vosin ?
12
Variables of Motion
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Other differences and similarities

• Time in air is called flight time and ½ of flight
  time occurs at ½ range
• So..it takes the same amount of time to go up as
  it does to fall down
• At ymax, Vyf 0m/s
• Still, only force acting on the is gravity
• Still, no acceleration in the x direction!

14
Practice Problem
A football is thrown with an initial velocity of
5.5 m/s at an angle of 49? above the horizontal.
1. How long did it take the ball to return to
the launching height? 2. What was the
maximum height the ball attained? 3. What was its
range?
Vyf 0 m/s
Max height
range
15
Lets Play Golf
16
Regents Physics

• Agenda
• Review HW Problems and Lab
• Circular Motion
• HW Read p. 163-168
• Problems p. 166 14-16

17
Circular Motion

• Question Can an object be accelerated if its
  speed remains constant?
• Whats uniform circular motion?

It is the movement of an object or point mass at
constant speed around a circle with a
fixed radius
18
Circular Motion

• Demo