1. Identify A Need
Teachers need a simple inexpensive-homemade tool to prove the relationship between mass and inertia. In other words, teachers need directions for building a simple inertia balance using materials commonly available.
Mass is the amount matter (stuff)in an object. Mass is also defined as the measurement for inertia.
UUM! Inertia is a measure of how difficult it is to change the motion of an object.
YIKES! This is getting a bit confusing. But don’t go away yet. I have an idea for making it easier to understand.
Mass is the measurement of the inertia “laziness” of an object in response to efforts made to change the object’s motion.
So far so good!
An INERTIA “LAZINESS” BALANCE swings back and forth in a horizontal direction. The rate at which the balance swings indicates how massive the object being swung is. Massive objects have a lazy, slow, sluggish swing. The more massive the more inertia an object has.
For fun we can say that massive objects are lazy and its hard to make them move and when they move it is slow and more sluggish than the swing of a less massive object.
3. Identify the Problem or Purpose of the Engineering Project.
Purpose: The build and calibrate an inertia balance.
Calibrating an inertia balance means to decide how many swings the balance makes for specific masses.
4. Determine how you will solve the problem or carry out the purpose of the project.
For example, in the diagram above, a jig-saw blade is used because it is so flexible. Note that the sharp teeth on the blade are covered with tape. This is for safety and if you experiment with such a blade, you need cover the teeth with protective tape.
The blade is taped to the side-corner of a cabinet. At the free end of the blade, a film canister is attached. The canister works well if the objects being massed are small enough to fit into the canister, such as coins.
The aim is to decide the number of swings the balance makes with different masses in the canister.
You do not want the objects to slide back and forth inside the canister, so cotton can be stuffed in the canister.
Decide on how you plan to build your inertia balance. List materials, and procedure to follow for its construction.
5. Build the Inertia Balance
This may just be a prototype–meaning that your first construction may not work as well as you wish, and will have to have changes. But, it may be the final product. Either way, Complete the construction of the inertia balance, and then test it.
6. Calibrate the Inertia Balance
Calibrating means to decide how many swings the balance makes for specific masses. The information will be used to make a graph that shows the swings the balance makes for different masses placed in the canister.
1. For 0-coins, add only the cotton stuffing to the canister. Pull the “canister end” of the balance to one side, and then release. At the instant you release the balance, start the timer, and start counting the vibrations (back and forth swings).
WOW!!!! Hope you are a multitasker!!! If not, ask someone to measure the time for you.
You could measure the number of swings in a specific amount of time, such as the number of swings in 10 seconds. Divide the swings by 10, and voila’ you have the number of swings per second.
Note: Leave space to record the mass of each number of coins tested. In the table shown, I have ?g where you will record the real mass of the coins you use.
2. Repeat step 1 using 1 coin. If there is no noticeable difference in the number of swings, add a second coin.
3. Continue adding coins and measuring the swings. You do not have to measure the swings of every single coin. In other words, you could measure the swings of 2, 5, 8, 12 and 15 coins. Just remember, the more information you collect, the more accurate will be your calibration.
4. Determine the mass of one coin using these steps:
(1) Using a food scale, measure the gram mass of 20 same coins.
(2) Divide the mass by 20 to decide the gram mass of one coin.
5. Determine the mass for each set of coins measured (shown in the data table). Record the mass in the data table.
6. Use your data table to create a graph (swings on Y-axis, and the mass of the coins on the X-axis).
1. Place the object in the canister. Be sure to add the cotton or what ever you used inside the canister when you calibrated the balance.
2. As before, pull the balance to one side and count its swings in 10 seconds. Divide the number of swings by 10.
3. Use the calibration graph to decide the mass of your object. Use the following instructions as well as the graph in the diagram.
Find the number of swings per second on the vertical scale, follow a straight line from the swings the line graph. Then, follow a vertical line down to the horizontal mass scale.
More Resources for Inertia Balances:
|Janice VanCleave’s Engineering for Every Kid: Easy Activities That Make Learning Science Fun|