Investigating Inertia

Jackie Sibenaller
Fergus Falls Senior High School
Fergus Falls, MN 56537
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Summary

In this inquiry, students will determine what inertia is and recognize how inertia affects objects. Students will first try to determine a definition of inertia based on a simple ordering activity and demonstration. They will also relate inertia to mass. In a separate series of activities, students will recognize how inertia affects a variety of objects.

Learning Goals

Goals: Students will compare and contrast the masses of objects to predict the relationship between inertia and mass. They will classify objects by their masses and illustrate the relationship between mass and change in motion. Students will synthesize their ideas to develop a definition of inertia based on manipulation of objects. They will design a model of inertia and test their models in other situations.
Concepts: Students will be able to organize objects based on their masses and interpret the relationship between mass and ease of movement. Students will use evidence from manipulating objects to determine a definition of inertia. Students will analyze their results to develop an experiment to demonstrate their understanding of inertia.
Vocabulary Words: inertia, mass, and force.

Context for Use

This activity is ideal for a ninth grade physical science course. Ideally, a class size of 24 would be great; allowing for six groups of four for the six stations. It is best to have stations set up at lab tables around the room so groups can move from one station to another easily. I use this activity during the physics portion of my curriculum. Students must have a background in mass and force before doing this activity. I think if could easily be adjusted or adapted for other grade levels and numbers of students.

Subject: Physics:Classical Mechanics:Newton's First Law
Resource Type: Activities:Lab Activity
Grade Level: High School (9-12)

Description and Teaching Materials

Day 1:
On each lab table have a variety of objects (a bowling ball, a large rock, a tennis ball, and a ping pong ball). Have students place them in order of hardest to lift to easiest to lift. In lab groups have students discuss why they placed them in this order and give reasoning for the order they placed them in. Have students draw the order in their notebook and give reasoning for the order below their drawings.

Demonstration with hanger and rubber balls: Place the middle of the hanger on a student's head and have him/her turn around quickly keeping his/her feet in approximately the same area. Ask the class what they notice about the movement of the rubber balls (they don't move much even though the student is moving quickly around). Tell students that this demonstrates inertia. Have students determine a definition of inertia in their lab group based on their observations.

As a class, decide what it is that makes some objects easier to lift rather than other objects. (mass is a measure of inertia)(inertia is the resistance to change motion)

Day 2:
Lab Stations:
1. A glass beaker half filled with water, a nickel, a penny, and a notecard. Drop the nickel/ penny into the beaker without tipping the paper. Try until you are able to get the nickel/penny into the beaker by moving the paper. Record your observations.
2. Raw egg and hard boiled egg in Petri dishes. Try to get the eggs to spin around quickly. Which one is easier to spin? Why? Try to stop the eggs by touching your finger to the top of the spinning egg. Which egg stops quicker? Why? Record your observations.
3. Empty 20 oz plastic bottle and a 20 oz plastic bottle half filled with water. Pull a smooth cloth or large piece of smooth paper out from under each. Which one was easier to pull the cloth out from underneath without moving the object? Record your observations.
4. Try to drop a tennis ball on a target as you run past the target. Mark a piece of paper with an X. Stand about 10 meters away from the target. Run about 10 meters toward the paper as fast as you can and drop the tennis ball on the target. Write observations about where the ball landed when you dropped it.
5. Stack five poker chips in a pile on top of each other. Knock the bottom chip out from underneath the other chips by hitting it with the thin edge of a plastic knife. You will need to do this quickly. You may not be successful in knocking just the bottom chip out on the first try. You may need to practice several times before you get it. (Explanation: The bottom chip will move because the force of the knife acts on it. Inertia will keep the other chips in the stack above it from moving with the bottom chip. The other chips will drop straight down to form a stack of four.)
6. Hang a large weighted object (1000 g weight) from a string. Tie a piece of thread around the weighted object. Slowly pull the thread toward you. Record what happens. Now pull the thread quickly toward you. Record what happens. (The thread should break and the weight should hardly move.)

Teaching Notes and Tips

This activity is a little time consuming to set up due to having a large number of stations with different items at each station. I have the stations set up in totes, ready to be used from year to year. In the past I have always given students the definition of inertia before they try to show how inertia works. By doing the stations now, students develop their own definition of inertia.

Assessment

Students will be assessed both informally and formally. Informal assessment is used to see if students are understanding concepts and procedures in their lab groups. Formal assessment is done through a series of individual questions listed below.

Questions:
1. What was the outside force acting in this activity?
2. At station 2, why was one egg easier to get started spinning and stop spinning? Explain your results in terms of inertia.
3. What would happen if you pulled the cloth/paper slowly at station 3?
4. Why did the tennis ball land where it did at station 4? What two forces are acting on the tennis ball? Draw a diagram of the path of the tennis ball as you dropped it while running by the target. Draw a diagram of how you would have to throw the tennis ball to hit the target if you were standing 10 meters away from the target.
5. What type of coin would work best for the activity at station 5 (dime, penny, nickel, or quarter)? Why do you think this type of coin would work best? Test your prediction.
6. Compare your results for pulling the thread slowly versus pulling the thread quickly at station 6. Explain your results.
7. In your own words write a definition of inertia based on the results of these activities.

Standards

MN Standard
9-12 Physical Science
2. Motion
2. Forces and object mass determine the motion of an object.
9.2.2.2.1 Recognize that the inertia of an object causes it to resist changes in motion.

References and Resources