Tuesday, January 17, 2017

This is the QR code to get you to the Physics 2017 PowerPoint presentations

Blizzard Bag #1

On February 7, 2017 - Please do the first blizzard bag since we just started new classes.
Factor Label Unit Conversion

Numbers alone, numbers without units, "naked numbers"  are seldom used.
One of your blizzard bag questions is to find examples when it is okay to use a number without a unit.

The factor label unit conversion method is a way to convert an amount with one unit into an equivalent amount with a different unit.  For example it shows how to convert from 200 cents to $2

If you do not have internet access, do the practice worksheet handed out in class and answer the questions below.

If you have internet access, go to the following website and do all the problems.  Make paper copies of each problem you do.  Also answer the questions below.

website:   Factor Label Practice Problems

  Read the article below "Naked Numbers Cost NASA" to understand why putting units with your numbers is important.  

Questions for all to do:

1.  Find times when it is okay to use a number without a unit.

2.  Comment on how the following story can be possible:

I was driving north from Vermont to Quebec.  After I entered Canada the speed limit changed from 65 to 100  so I slowed down a little.

3.  Give an example when   1 = 1000

4.  Find the unit that currently has the record for being the largest.

5. Why use units with your number?

Bring responses on paper to class tomorrow

Naked Numbers Cost NASA
Mars Climate Orbiter Gone Forever

After a nine month trip to Mars, the Mars Climate Observer spacecraft
was lost as a result of Naked Numbers.  Numbers communicated from
Lockheed Martin in Colorado to NASA's Jet Propulsion Lab in California
were left unit-less.  Naked numbers, being completely meaningless,
left engineers to guess at their meaning.  The confusion created by
improperly dressed numbers caused the loss of a $125 million
spacecraft and the waste of a 9 month journey to Mars.  Thankfully, no
lives were lost.

Lockheed Martin was sending daily course adjustments to the Jet
Propulsion Laboratory with numbers that should have been wearing the
English units of "pound-seconds" to describe the amount of impulse
which should be applied to the spacecraft to adjust its course.  When
these naked numbers arrived at the Jet Propulsion Laboratory engineers
assumed that these were specifying the amount of impulse in metric
units of "newton-seconds".  Simply labeling the units that were being
used would have prevented this tremendous loss.  A group of physics
teachers in Ithaca, New York hope to bring a proposal to Capitol Hill
that would ban the use of naked numbers in the United States.  Further
efforts are being used to convince the United Nations to apply a
similar law to the World.  Until such a law is passed, physics
teachers everywhere will have to settle for simply marking answers as
wrong if they are not labeled with proper units.  Math teachers are
urged to contribute to the solution not the problem.

Mars Orbiter Loss Linked to Math Mistake

Newsday - Ithaca Journal
October 1, 1999

Washington - The loss of the Mars Climate Orbiter as it approached
Mars last week is being blamed on a goof that could have tripped up a
novice science student - confusing English and metric units.
    A preliminary investigation has found that two spacecraft teams -
one at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the
other at a Lockheed Martin facility in Colorado where the spacecraft
was built - unknowingly were exchanging some vital information in
different units of measurement.
    Thomas Gavin, deputy director of space and earth sciences at JPL,
said in an interview Thursday that the mistake involved information
being used to make tiny corrections in the spacecraft's orientation
during its 9½-month cruise to Mars.
    Twice a day during the cruise to Mars, tiny thrusters on the
spacecraft were fired briefly to counteract the effects of solar wind
and other forces on the spinning of the flywheels.  The spacecraft
team in Colorado used English units called pound-seconds to describe
the small forces.(bad scienc writing)
    That data was shipped via computer to JPL where the navigation
team was expecting to receive the information in newton-seconds, a
metric measure of force. (bad science writing)
    Two Cornell University scientists calibrated the camera on the
spacecraft, but neither scientist had any involvement in the
measurement mistake.


Here is the link to the website that has the chapter slide shows!

The Physics Slide Show Website

Monday, January 16, 2017

Mr. Merrell's Blizzard Bag #2


Purpose: To experiment with virtual  projectiles, form a hypothesis and design your own experiment
.
Introduction:  On the University of Colorado website you will gain  access to the following items: a tank shell, a golf ball, a baseball, a bowling ball, a football, a pumpkin, an adult human, a piano and a Buick. You will be able to LAUNCH them. This could be fun! It's your turn to design an original laboratory activity to test a specific hypothesis.  See what things you can change (independent variable).  See what changes when you change your independent variable (your dependent variable).  Pick just one IV and one DV.  Keep track of the numbers.  Graph the DV on the vertical axis and the IV on the horizontal axis.  Look for a relationship.

Materials: Projectiles simulation, University of Colorado 

Procedure:

  1. Go to the Projectiles simulation, University of Colorado and try out some launches.
  2.  Select a purpose for your lab or formulate your own testable hypothesis.
  3. Design your experiment based on the purpose or hypothesis you have formulated. It is important that you limit your experiment to only two variables that can be easily measured and compared, all other variables should be kept constant.  For example, you can choose to vary the angle and measure the range (horizontal distance traveled).
  4. Be sure to include the following sections in your design: Title, Purpose or Hypothesis, Introduction, Materials, Procedure, Data Table, Graph, Questions, and Conclusion.

Saturday, January 14, 2017

This car was involved in a car crash.  In all collisions (and explosions) there is Conservation of Momentum.  The total momentum in the system before the crash equals the total momentum in the system after the crash.  The system in this case includes the tractor trailer which crashed into the car and the Earth.  The study of this conservation begins with straight line collisions and explosions.

If m1 is the mass of the first object, then you know what m2 is.
If v1 is the velocity of the first object before the crash, then you can guess what v2 is

Let v1' be the velocity of the first object after the crash.
Let v2' be the velocity of the second object after the crash.

You now have all of the symbols to make the one dimensional momentum conservation equation.

Momentum before = Momentum after becomes

m1v1  +  m2v2     =    m1v1'  +  m2v2'

Here is a twist:  if the two masses stick together, then they have the same velocity v' immediately after the crash (before transferring momentum to the Earth).   In this case

m1v1  +  m2v2     =  (m1 + m2) v'

Try some problems:


Saturday, January 7, 2017

Momentum and Conservation of Momentum

Does this car have inertia?  momentum?
The car is at rest.
Inertia is a measure of mass.  It is the tendency for an object to resist a change in its motion.
Momentum is defined as mass times velocity.
We use the letter p for momentum.  p = mv