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Using a Triple Beam Balance

By Leroy Webb,2014-09-30 07:12
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Using a Triple Beam Balance

    Slide Your Mass Over

    Learning and Applying the Skill of Using the Triple Beam Balance

Section A Skill Acquisition

General Introduction to Skill

    A balance is generally used for weighing out small amounts of chemicals to use

    in solutions and determining the mass of different objects in physics in grams.

    Learning how to use a balance is important for collecting data or information

    and for ensuring accurate mass measurements.

Curriculum Objectives

     S2-0-5a Select and use appropriate methods and tools for collecting data

    or information.

     S2-0-5b Estimate and measure accurately using Systeme International

    (SI) and other standard units.

     Include: SI conversions.

     Riders Beams Pointer ; ; ; Balance pan ; Scale Adjustment

     screw

Special Safety, Care, and Handling Aspects

     Make sure the riders are at zero before carrying the balance.

     Carry the balance with both hands and keep it horizontal.

     Do not place anything hot directly on the balance pan.

     Never pour chemicals directly on the balance pan.

     Place balance on a level, sturdy surface and away from heavy traffic.

    Setting Up the Balance

     Make sure the riders are at zero.

     Check to make sure the pointer swings freely along the scale.

     Use the adjustment screw to obtain an equal swing of the beams, if necessary.

    The Procedure with an Analogy

    Look at the riders on your balance. These will be used for balancing the weight of an object on the balancing pan. One is 100 grams, one is 10 grams and one is 1 gram.

    Think of it this way: if you worked at a bank with only $100 bills, $10 bills, loonies, and small change and you have to give somebody $653.50, they would probably appreciate it if you gave them the fewest amounts of bills possible. How would you do this? You would start by giving them six $100 bills, then five $10 bills, then three loonies and small change last.

    When using a balance, you do not know in advance how many grams an object weighs, but you will “hand out” the “amounts” in the same way.

    1. You would start by moving the 100 gram rider over one at a time (making

    sure to fall into a notch) as far as you can without tipping the scale (if you go

    too far, the balancing pan will lift up because you went too far and need to

    move back one notch). This is like handing out one $100 at a time, making

    sure not to give too much.

    2. Then, you would move the 10 gram rider, making sure to go as far as you

    can (falling in a notch) without “giving too much.” This is like handing out

    the $10 bills.

    3. And last, you would slide the 1 gram rider over until a perfect balance is

    indicated by the pointer and scale marks being lined up (this rider has no

    notches so that it can be precise). This is like handing out the loonies and the

    small change.

    4. To find out the total mass of the object, you simply need to add up the three

    amounts indicated by the riders. For example, if an object balanced with the

    100 gram rider in the third notch from zero, the 10 gram rider in the fifth

    notch from zero, and the 1 gram slider at 3.5, the total mass of the object

    would be (100 grams x 3) + (10 grams x 5) + 3.5 grams = 353.5 grams.

    Skill Development

    1. Have each student in your group pick an object from your possessions to

    weigh. List the objects chosen and your estimation of their masses in the

    table.

    Object Estimated Mass Actual Mass

    2. Have each person determine the weight of their object using the balance and

    fill in the actual mass column of the previous table.

    3. Explain your procedure for finding the mass of your object. Include all

    calculations. You may use drawings to assist your explanation.

Section B Skill Application

Background Information

     Momentum is the product of mass and velocity. Momentum is also conserved.

    This demonstration and following investigation is designed to explore the two

    factors of momentum in more detail for the purpose of deepening understanding

    and developing inquiry and investigation skills.

Curriculum Objective

     S2-3-08 Define momentum and impulse and qualitatively relate impulse

    to change in momentum for everyday situations.

Materials

     Measuring tape

     Metre stick

     Scale

     Chair

     Basketball

     Ping-pong ball and fussball about the same size

     Balls of a variety of masses (eg. baseball, tennis ball, golf ball, floor hockey

    ball)

Safety Suggestions

     A “spotter” for the student standing on the chair

     A few “ball catchers” to catch the flying ball

Introduction Activity

    Get into groups of 4 or 5. Perform the activity and discuss and record your

    answers to the following questions as a group.

    1. Begin by holding a metre stick upright from the floor. Hold a basketball so

    that the bottom of it is at exactly one metre beside the metre stick. Predict

    how high the basketball will bounce when released. Observe what the

    height of the lowest point of the ball is at the highest point of the bounce

    after the ball is released.

    2. Repeat this process for a ping pong ball.

    3. Place the ping pong ball on the top of the basketball and predict what will

    happen when this is released at one metre. Explain your reasoning for your

    predictions.

    Prediction: _______________________________________________________

    Explanation: _____________________________________________________

    ________________________________________________________________

    ________________________________________________________________

    4. Drop the basketball with the ping pong ball resting on top (you may have to

    hold it there with a finger on top) and observe what happens a few times.

    Try to explain it if it was different than your prediction.

    Explanation: _____________________________________________________

    ________________________________________________________________

    ________________________________________________________________

    In this activity you observed that when a big ball with a small one on top of it is

    released from a one metre height, the big ball remains stationary on the floor

    and the small ball goes flying. This is because of the momentum of the object.

    The momentum of an object is affected by its mass and its velocity. This is

    why when a large moving object (the two balls together) breaks apart into a

    smaller moving object (the small ball) and a stationary object (the basketball),

    this smaller moving mass takes all the momentum of the original object and

    results in a much larger velocity.

Inquiry

    1. What variables from the demonstration could you manipulate to learn more

    about momentum (list at least three)?

    ______________________________________________________________________________________________________________________________________

2. Suggest at least three inquiry questions you could investigate based on

    question 1.

    ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Some inquiry questions to consider are:

    a. Does the mass of the top ball affect the height of the bounce?

    b. Does the mass of the bottom ball affect the height of the bounce?

Choose one of the suggested questions for investigation (a or b from above).

3. Which question have you chosen to investigate?

    ___________________________________________________________________

    4. What is the variable you will manipulate? ______________________________

    5. What variables will remain the same? __________________________________ ___________________________________________________________________

    6. What is the effect you are measuring (what is the result of manipulating the

    variable from #4)? _________________________________________________

    7. a. What will you use to measure the variable you will change? ______________

     b. What units will you use to measure this variable? ______________________

    8. a. What will you use to measure the result? _____________________________

     b. What units will you use to measure the result? _________________________

    9. List the materials you will need. ______________________________________ ___________________________________________________________________

    10.List any safety precautions you must take while conducting this investigation. _________________________________________________________________________________________________________________________________________________________________________________________________________

Gather the materials listed in #9.

Procedure

    List the steps of your procedure, making sure to perform multiple trials of

    each demonstration to ensure accuracy. You may also use pictures or diagrams to clarify steps. You are provided with and are expected to make use of the table and graph paper provided.

Observations

Trial #

Conclusions

    11.Explain the outcome of your inquiry, based on the table and graph you have

    made.

    ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

    12.Momentum is the product of mass and velocity. How does this investigation

    support this statement?

    ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

    13.What is another question you would like to investigate? ___________________________________________________________________

14.What is your prediction of the results?

    ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

References

     http://www.hometrainingtools.com/articles/how-to-use-triple-beam-balance-

    teaching-tip.html

     http://ideaplace.org/Chemistry/ChemLabs/Balance.html

     http://www.physics.smu.edu/~scalise/apparatus/triplebeam/

     http://www.newton.dep.anl.gov/askasci/gen99/gen99154.htm

     http://findarticles.com/p/articles/mi_gx5226/is_2002/ai_n19143748

     http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/momtoc.html

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