21. “G” WIZZ

from Come Fly With Me – Exploring Science through aviation and aerospace concepts.

SUBJECT: Science
GRADE: 7,8,9
GROUP SIZE: Small _
TIME: 45 minutes
TYPE OF ACTIVITY: Student Investigation
TEACHING STRATEGY: Guided Discovery
CONCEPTS: Weight Mass
SKILLS: Construction Collecting and Interpreting Data
Objectives: To distinguish between weight and mass; to develop techniques of finding mass when there is no weight; to build equipment to determine mass when a balance will not work.

Materials: For each group of three students: 1 hacksaw blade; 1 small “c” clamp; 1 small bolt with two nuts to fit the hole at the end of the hacksaw blade; several washers of the same mass; a stop watch; data sheet; a table or chair to fasten the “c” clamp to:(You can build a stand as in the diagram and weight it with bricks).

mass measurer instructions

Teacher Background Information:

The weight of an object is a ways a measure of the pull of gravity on that object (the attraction of one mass to another). On the Moon, objects weigh 1/6 of what they do on the Earth. In space, some 300 kilometers above the Earth, objects weigh about 1/3000 of what they do on the surface. (Essentially, they are nearly weightless.) A 210 pound astronaut would weigh about 1 ounce. Many of the experiments done on the health of astronauts required finding their mass while in space. Mass is measured in grams. Grams are defined as the mass of one cubic centimeter of water. You are measuring the amount of matter in a given space when you measure mass. The amount of astronaut does not change while in space from that while on the Earth or on the Moon. His or her mass would be the same – only the weight (attraction of gravity) would change. So, how can mass be measured when there is no weight???
Procedure:

  1. Attach a hacksaw blade to the leg of a chair or a stable platform of some kind with a “c” clamp.
  2. Fit a bolt through the hole at the opposite end of the blade and secure it with a nut.
  3. Attach a washer to the bolt and secure it with the other nut.
  4. Pull the blade to one side and release.
  5. Have a student count the number of oscillations of the blade while another student keeps time with a stopwatch.
  6. Have another student keep track of the swings per minute on the data sheet.
  7. Add washers to the blade, one at a time until several bits of data have been collected.
  8. Make a calibration chart of the results by graphing the data.
    Note: The hacksaw blade oscillations are independent of gravity and are dependent on the elasticity of the metal. The same number of swings would be recorded on the Moon or in space. FIND THE MASS OF AN UNKNOWN.
  9. Place a small ball of clay on the mass tester.
  10. Measure the number of swings per minute and refer to the calibration chart to determine the mass in washers.
  11. Find the mass of the washers and compute the mass of the clay in grams.
  12. Place the clay on a balance and check your calculations to see how accurate your measurements were.

Note to the Teacher: You may wish to tie this lesson in with one on the arbitrary nature of systems of measurement.
Extensions: The astronauts use a device similar in operation to the simple device the students produce in this lesson to measure their mass in space. Have the students find out more about it by investigating some of the experiments performed on Skylab.

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