Soda Straw Balance

Experiment Title: Soda Straw Balance

Grade Level: 3rd Grade

Process-oriented objectives: The students will be able to measure weights of very small objects using the soda straw balance.

Processes addressed: observing, communicating, measuring, predicting, and inferring

NSES Content Standards: A &E

Source of Experiment: Formulating and testing hypothesis; experimenting and constructing model.

Materials: straws, bolts or screws, pins, equal sided blocks, and scissors.

Safety Precautions: Teacher should help students insert pin through straw and oversee the cutting of the tip of the straw.

Introduction to activity: Ask the class to guess how much hair an average person has. Ask the class how many strands of grass are on their lawn or backyard. Tell the class that today, they will be able to measure the smallest objects.

Description of Activity: Cut one end of the straw at an angle to form a "pan." Put the bolt in the other end, and screw it partway into the straw. Run the pin through the straw, just barely forward of the screw and a little bit above the center of the straw. Balance the straw between the two blocks and screw the bolt in or out very slowly until the straw rests at a suitable incline. This balance can measure weights as little as 1/1000 of a gram.

To find the weights of things using this balance, weigh a sheet of graph paper on a gram balance. Count the number of squares in the sheet, and divide the weight by the number of squares to obtain the weight of one square. Cut out one square and place it in the pan of the soda straw balance. Set up a tongue depressor next to the tip of the balance and record the positions of the tip of the balance without the square of graph paper and with the square of graph paper. Divide the space between these two positions into 10 equal segments, and calculate the weight represented by each segment. ( Each division is equal to 1/10 of the weight of the square of graph paper.)

Discussion question: Ask students which objects weigh more than others and why.

Expected conclusion: Students will know the difference between the weights of certain objects and how this weight differs when other variables are added.

Evaluation/ Assessment: Students can be given objects to make predictions about. After they have made their predictions, they can see if their predictions are correct by using the balance.

Applications to real life: Insight into weights and measurements of small everyday things.