October 3, 2005

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October 3, 2005

• Homework
• Review ALL labs and notes nightly. FINAL EXAM
  IN four PERIODS.

You will need a calculator today.
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Newtons 3rd Law

• When one body exerts a force upon a second body,
  the second body exerts an equal and opposite
  force upon the first body.

Pushing a Car
Action-Shove a car forward
Re-action-the car pushes back on you with equal
force
Rowing a Boat
Action-Push the water back with paddle
Re-action-the water pushed forward on the paddle
making the boat propel forward
Shooting a Gun
Action-exploding gun powder pushes bullet forward
Re-action-the bullet pushes the gun backwards
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Momentum

• Newton called this quantity of motion.
• Momentum mass x velocity
• p mv
• If either mass or velocity increases, momentum is
  increased.
• Momentum units come directly from the mass and
  the velocity and are written right next to each
  other.
• Example kgm/sec gmm/sec

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1. What is the momentum of a bird with a mass of
.018 kg flying at 15 m/sec north?
p mv p .018 kg x 15 m/sec p .27 kgm/sec
p mv p 50 kg x 100 m/min p 50000 kgm/min
2. A 50 kg child is walking with a velocity of
100 m/min. What is the momentum of the child?
3. A golf ball travels at 16 m/sec, while a
baseball moves at 7 m/sec. The mass of the golf
ball is .045 kg and the mass of the baseball is
.14 kg. Which has greater momentum?
p mv p .045 kg x 16 m/sec p .72
kgm/sec (golf ball) p mv p .14 kg x 7
m/sec p .98 kgm/sec (baseball) The baseball
has more momentum.
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4. The momentum of a boat is 100,000 kg m/sec
with a velocity of 5 m/sec. What is the mass of
the boat?
p mv 100,000 kgm/sec m x 5 m/sec 5 m/sec m
20,000 kg
Use the remainder of class to complete labs 25
26. These are the last two in this
series! HOMEWORK Review completed labs, work
on practice problems assigned on Friday, study
all vocabulary, and memorize all formulas.
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Lab Goals Today

• You must complete labs 25 and 26.
• If you have extra time at the end of the period
• Look back over labs 17 26. (We did not do
  19.)
• Do you have the objectives?
• Do you have the variables?
• Do you have the QUESTIONS COPIED?
• Have you answered EACH QUESTION fully? Did you
  EXPLAIN your thinking?
• Do your answers support the objectives?
• What grade would I give you for each lab?

• 3. Study for the test! Write your own
  questions. Quiz your neighbor on vocabulary and
  formulas. Do you know the formula for
  speed/velocity? Acceleration? Momentum?