Download Honors Physics 19 Oct 2009

Honors Physics 19 Oct 2009
• Today and tomorrow: Virtual Projectile lab
• This is a mandatory lab assignment!
• Please turn in your free-fall graphical analysis
lab work if you haven’t already!
Honors Physics 20 Oct 2009
• Complete Virtual Projectile Labs
– Turn in today if finished
– Complete for homework and turn in tomorrow if
you need more time.
– Tomorrow: Projectile challenge – can you predict
where your projectile will land using equations of
motion?
Honors Physics 21 Oct 2009
• Today: Projectile challenge – can you predict
where a projectile will land?
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TOOLS
dx = vxt (from EQ 2)
dy = ½ gt2 (from EQ 3)
Timer, Board, Ball, Cup, Meter Stick
Idea behind the lab
• Calculate the distance that a projectile travels
knowing the velocity of launch and the height
• Solve the y equation for t
• Roll a ball using a ramp to determine its
launch velocity
• Plug this t into the x equation to solve for the
x distance
• Put a cup this distance away from the edge of
the table and try to catch it.
Honors Physics 22 Oct 2009
• Today: More on vector analysis – and using
trigonometry
• Homework: Practice B problems 1-4 on page
92
More on vectors
• Vector quantities have magnitude and
direction – they are sometimes indicated by
little arrows above the variable
• Addition of two vectors is NOT the same as
adding scalar terms. You must use graphical or
trigonometric methods (if you take a linear algebra
course in college, you’ll learn another way to add vectors
using matrices)
Vectors continued
• Adding two or more vectors gives you a
“resultant,” so we say things like, “we resolve
these vectors,” and so forth.
• Vectors can be moved for analysis, as long as
they aren’t “turned”
• Vectors can be added in any order, but always
“tip to tail.”
• You can multiply a vector times a scalar,
getting a new vector
Rules for right triangles
• a2 + b2 = c2 where c is the hypotenuse of a
right triangle, and a and b are the short sides
• Sohcahtoa 
– sin θ = opposite/hypotenuse
– cos θ = adjacent/hypotenuse
– tan θ = opposite/adjacent
Using trig - examples
• A plane flies north at 100 m/s while a wind
blows to the east at 30 m/s. What are the
resulting speed and direction of the plane?
• A cannon ball is fired at a speed of 100 m/s at
an angle of 30 degrees with respect to the
horizon. What are the x and y components of
velocity
Honor Physics 23 Oct 2009
• First – Homework check & warm-up
• An arrow is fired at a speed of 40 m/s at an
angle of 20 degrees above the horizon. What
are the initial x and y components of
velocity?
• Together: How high does it go? How far does
it go? What if you fired it from a 30 m high
cliff?