cahier physique - physics workbook

HOW MASS IS RELATED TO INERTIA ? FILL BLANKS FOR FULL CREDITS

Newton’s first law states that an object at rest to remain at _____ , while an object in motion tends to remain in _____.
Unless acted upon by a _______.
This property of matter is called_______. An inertia balance is a device that makes use of this property to determine the mass
of an object. The period T of an inertia balance is directly related to the amount of mass attached to the
balance. The period is the amount of _____ it takes for one complete swing of the balance (or cycle).

PURPOSE: You will learn how an inertia balance is used to determine mass. You will find the mass of an object using your inertia balance.
Then you will check your measurement.

SKILLS: observing, measuring, graphing

MATERIALS: inertia balance (that is a spring and its mass holder)
, masses (5) , graph paper, stopwatch, masking tape, C-clamp, unknown mass (2)

PROCEDURE

1. Clamp the inertia balance to the ring stand so that it can swings freely.

2. Measure: Secure a 150g = (50g for the holder + 100 mass to the balance). Pull the mass about 5cm back and release it. Time 10-swings of the balance. Record your time in table 1.

3. Repeat step 2 for 250 (add 100g) , 350 (add 100), 400 (add 50) Then repeat step 2 for the 1 unknown mass.

4. Calculate the period by using the formula: period = time for 10 swings / 10
Record the period and the period squared for each mass in table 1.

5. Hang your unknown mass and record the period and the period squares.

T unknown mass = _____________________ T² = __________________

6: graph: Make a graph of period squared vs mass for the 5 known masses.
That means: x = mass and y = (period)^2.You may want to multiply your y-values by 10 to make it easier to graph.
Trace the best fit line. You can use your TI.

TABLE1: (the holder is 50 g, add 100g weighs )

Mass on balance (g) Y	Time for 10 swings (sec)	Period (sec)	T² = Period² (sec²) X
150

ANALYSIS

7. Take T² (period squared) as your X and the mass as your Y
Plot the points (X, Y) on a graph paper. don;t connect the points. Label the axis and title the graph.
watch the scales of the axis. Don't forget the units. (again T²(s²) is the X and the mass (g) is the Y )

8. Trace the best fit line. Going through the points. Use a ruler. Note that you need to force the line to
go throuth the origin because if mass = 0 there is no swing so no period.

9. Find the slope. (the y-intercept has to be zero because X=0 then Y=0).
slope = ______ g/s². You can use your TI.

10. Find the equation of the line. Y = ___ X
SO (mass) = _________ x (period)²

11. Use this equation to find the unkwnon mass. (you are using the system you built as a scale).
You are solving for Y (mass) and you are given X (the period²for the unknown mass)

Unknown mass measured = ____________________________

12. Using a spring scale,. find out the true mass of the unknown mass.

True mass = ____________________________

13) Are you close? Error% = |true - your measure|/true x 100 = _______%
So it your scale accurate ?

10) An object on the balance makes 15 swings in 10 seconds. What is the period of the balance ? follow steps.
REmember the period is the time for 1 swing in seconds. you find T = _____ s (se hint)
(hint: solve the proportion: 15 swings is for 10s so 1 swing is for ______ = T)
Find T² = ___ so mass = ______. (see equation in 10 )