cahier physique - physics workbook

1) INTRODUCTION

We are going to find, experimentally, the value of pi (3.14) using an indirect method of measurement.
Maybe you remember that the circumference of a circle of radius R is C = _____ (use pi and R in the formula).
The diameter of a circle of radius R is __________. So the ratio (to get a ration you divide) of circumference / diameter = C/2R = __________.
(hint: cross our 2 R ). We are going to use this fact to find the value of Pi hands-on.

PROCEDURE: you need: circular cylinder like beakers of different size, any round object + meter tape (ask me) +ruler (not a meter stick !!)

1) Pick one cylinder and one student (in the team) find the diameter in cm using a ruler and the circumference using the measuring tape.
To find the diameter never use the ends of the ruler as endpoints for the distances measured. Make the lines of sight
to the ruler as nearly perpendicular to the scale as possible.
KEEP 2 DECIMALS. (estimate the second one)
Diameter D1 = _________ cm and Circumference C1 = ___________cm

2) The other students in the team record the same measurements. You should have 3 or 4 values for C and D.
hint: C = D x pi (circumfrenc = 2 pi R or 2R pi or D x pi with pi = 3.14)
D2 = _________ cm and C2 = ___________cm
D3 = __________cm and C3 = ___________ cm
D4 = __________ cm and C4 = ___________ cm

3) Find the average D = ________cm and C = __________ cm (D = (D1 + D2 + D3) / 3 and C = ( C1 + C2 + C3 ) / 3 )
REport in the TABLE below/ first row

3) Repeat step 1 to 3 for the other circular containers or objects.

4) Compute the average of all the ratios.

TABLE

objects(description)	diameter (cm) =D	circumference (cm) = C	ratio C / D

AVERAGE RATIOS : ___________
ANALYSIS

1) Find the ratio Circumference / diameter = C/D for each container and complete the table.

2) Find the average of all the ratios. Keep 2 decimals. average ratio = __________ (no unit)

3) What number this ratio represent ?

4) Using your TI write a better approximation for the number pi = ___________ TI

4) Do you think the goal of the lab was achieved ? (by the way, what was the goal ?)

GOING FURTHER

1) 28 grams of grass pollen contains approximately 6 billion grains of pollen. (hint: 1 billion = 1,000,000,000)
Approximately, how much does one grain weigh ? Use scientific notation. m = _________ grams
hint: use proportion

2) The world's smallest commercial fish is the sinarapan (from Philippines).
If you ordered one kilogram of sinarapan, you would receive approximately 154,000 fish.
Approximately how much does each fish weigh ? in scientific notation : m = __________ kg = ____________ g = ___________ mg
hint: 1kg = 1000g 1 g = 1000 mg USE proportions again.

source: a website about Philippines biodiversity. check the pygmy frog.

4) from ScienceDaily (Oct. 7, 2008)

An unexplained broken symmetry of the same kind lies behind the very origin of the cosmos in the Big Bang some 14 billion years ago.

If equal amounts of matter and antimatter were created, they ought to have annihilated each other.

But this did not happen, there was a tiny deviation of one extra particle of matter for every 10 billion antimatter particles.

It is this broken symmetry that seems to have caused our cosmos to survive.

So if we are here today, it is because there war one extra particle of matter (vs anti-matter) for
every 10 billion particles of anti matter. WRite this ratio in scientific notatation.
ratio = _________ matter/anti matter (divide )

5) see image below./ challenging problem. not required. For those who really enjoy Math and Sciences. you can skip it.
The most massive tree in the world is the General Sherman giant redwood in Sequoia National PArk, California.
It has been estimate to have a weight of about 2,755 tons.
A) How do you think you could estimate the height of the tree ?
(hint: see previous lab about indirect measurement)

B) Once you have the height how could you estimate the volume of the tree ?
hint: Think a tree is being a cylinder. volume = base x height with base = pi R² .

C) Suppose you take a piece of the tree. (a piece of branch). Can you find its mass in grams ?
Can you find its volume ? how ?
hint: think water displacement.

D) How can you estimate the mass of the tree now ? You have the small mass and the small volume of a small piece and the large volume of the
whole tree. Can you find the mass of the whole tree ? Which formula you can use?
hint: remember how you found the mass of the moon ?

E) After a trip to California (or a trip to Wikipedia) you find out that:
diameter of the tree is about 4.75 meters (average), so radius R = ______________. The area of the base is __________ m² (hint: pi R² = base)
The height if the tree is about 84m. So the volume of the tree is about V = _________________ m³ (round to the nearest one) (hint : volume = base x height)

You found out the ratio m / v = (small mass) / (small volume) = (mass of the piece of tree) / (volume piece of tree) to be 1852 g/cm3
(this is called the density, we will study that lateR)
Can you find the mass of the tree in grams ? Mass = _______________ grams then in kg Mass = __________kg (divide by 1000)
then in tons Mass = _________ tons (divide by 1000). Round to the nearest one.
hint:: 1852 small mass/ small volume = Large mass / Large volume or 1852 = M / V you have V (volume of the tree), solve for M (mass of the tree)
Same methodology than for the Mass of the moon.

source photo:http://www.cwrl.u
Texas.edu/~bump/RHE309K/jackie/PHOTO3.htm