Read the following directions for using and reading a triple beam balance.  Perform the activities.  Then answer the questions.

Before starting, make sure the triple beam balanced is balanced.  With nothing on the pan, the pointer should be lined up with the mark on the side.

Measuring directly
    a.  Place a washer on the pan of the balance.  The beams will rise and the pointer will point above zero.
     b. Move the rider on the middle beam one notch at a time until the pointer drops and stays below zero.  Move the rider back one notch.  The reading for that middle rider is _________

     c.  Move the rider on the back beam one notch at a time until the pointer again drops and stays below zero.  Move the rider back one notch. The reading for that back rider is _________

     d.  Slide the rider along the front beam until the point stops at zero. (be patience).  The mass of the object is equal to the sum of the readings on the three beams.  The reading for that front rider is ________

     e.  Record the mass to the nearest tenth of a gram. ________________

     f.  Return all riders back to zero before taking the washer off the pan.

Measuring by difference
     a.  Using the above method, measure the mass of the beaker. Record the mass ________.   Return all riders back to zero before taking the washer off the pan.

     b.  Fill up the graduated cylinder to 25 mL of water.  Pour the 25 mL water into the beaker.

    c.  Place the beaker with the water onto the pan of the triple beam balance.

    d.  Using the above method, measure the mass of the beaker with the water.  Record the mass _________. Return all riders back to zero before taking the washer off the pan.

     e.  Determine the difference between the two measurements and record to the nearest tenth of a gram. ________.
 

Measuring out
    a.  You are being asked to measure out 25 grams of sand.  In order to get exactly 25 grams, following the instruction carefully.
    b.  Using the previous method of measuring, measure the mass of the weighing paper.  Record the mass ______.
 
    c.  Keep the weighing paper on the pan and keep the riders in their current location.  Add together the 25 grams and the measured mass of the weighing paper.
                                                25 grams (sand)  +  ___________grams (weighing paper) = ________grams
   d.  Move the rider to the new mass.  The beam will no long be balance. (that's ok - we will fix that in the next step).
 
    e. Start adding sand (very slowly) to the weighing pan until you reach a balance.
 
 

QUESTIONS

What does it mean when the pointer of the balance reads "zero"?
 
 
 
 

What a rock is balanced on the triple-beam balance.  The riders on the three beams point to (middle rider) 300 grams; (back rider) 60 grams; (front rider) 3.5 grams.  What is the mass of the rock?