Measuring Mass
A Simplified Balance
Topics: Measurement
Physical Properties, Mass
How do you get really comfortable with measuring mass? Practice, practice, practice.
Materials List
 1 Plastic tube,
50 cm (20”) long
 2 Water bottle caps
 2 Thin straw pieces
~5 cm (2”) long
 1 Cork
 1 Toothpick
 2 base/pivot pieces
 2 Water bottle caps
with holes
 4 Jumbo paper clips
 Hot glue and/or
Rubber Bands
 Objects to measure
 Measurement
pieces (cm cubes,
pennies, wood
cubes, paper clips)
This activity can be used
to teach:
 Science &
Engineering Practices
(Next Generation
Science Standards:
Grades K-8)
Insert toothpick
pivots here
Top View
Side View of Base
Assembly
1.
2.
3.
4.
5.
Hot glue the 2 water bottle caps (open-side up) onto the ends of the plastic tube.
Break the toothpick in ½ and insert each piece into opposite sides of the cork.
Hot glue the cork onto the plastic tube at the center point.
Hot glue the base/pivot pieces onto water bottle caps with holes.
Position the bases close enough to hold the plastic tube assembly when toothpick
pieces are inserted into top sections of base pieces (see diagram).
6. Alternate assembly: Use rubber bands to secure the cork and base/pivot pieces.
7. Insert 2 paper clips into each end of the plastic tube and secure thin straw pieces
to each side of the tube to help “zero” the balance.
To Do and Notice
1. “Zero” the balance before use by positioning the rubber-banded straw pieces
along the plastic tube as required.
2. Place an object to measure in 1 cup.
3. Add gram cubes (or equivalent) to the second cup until the 2 sides balance to
determine the object’s mass.
The Science Behind the Activity
The 4 general properties of matter are: volume, density, mass, and weight. Mass
measures the amount of matter in an object. The Metric unit of mass is the gram (g).
By definition, 1 milliliter of water at 4° C has a mass of 1 g. For larger objects,
kilograms (kg) are the preferred units: 1000 g = 1 kg. A large paperclip has the mass
of about 1 g, making them a decent substitute for gram cubes or other standardized
manipulatives.
An object’s mass is the same anywhere in the universe. An object’s weight depends
on the strength of the gravitational field at its location. For example, an apple’s mass
does not change, but the apple’s weight on the Moon would be 1/6th of the weight on
Earth, because the Moon has less gravitational pull. The Metric unit of weigh is the
Newton (N). An object’s weight at Earth’s sea level = mass (in kg) x 9.8 N/kg. On
Earth, a person’s weight in N is ~10 times their mass in kg!
Taking it Further
To create a device to measure volume (space taken up by an object), see the RAFT
Idea sheet Graduated Preforms.
Web Resources (Visit www.raft.net/raft-idea?isid=218 for more resources!)
Balance designed by Michael Pollock (RAFT), written by Coral Clark (RAFT)
Copyright 2014, RAFT