PHYSICS SEMESTER ONE

AIR TRACK LAB

Conservation of Momentum and Energy

Lab format: this lab is a remote lab activity

Relationship to theory:This activity involves the study conservation of energy and momentum in collision

Instructions for Instructors: This protocol is written under an open source CC BY license. You may use the procedure as is or modify as necessary for your class. Be sure to let your students know if they should complete optional exercises in this lab procedure as lab technicians will not know if you want your students to complete optional exercise.

Remote Resources: Primary - Airtrack, Secondary - None.

Instructions for Students: Read the complete laboratory procedure before coming to lab. Under the experimental sections, complete all pre-lab materials before logging on to the remote lab, complete data collection sections during your on-line period, and answer questions in analysis sections after your on-line period. Your instructor will let you know if you are required to complete any optional exercises in this lab.

Contents

Learning Objectives

Background Information

Equipment

Preparing to Use the Remote Web-based Science Lab (RWSL)

Introduction to the Remote Equipment and Control Panel

Pre-Lab Questions:

Experimental Procedure:

Exercise 1 – Kinetic Energy and Momentum in an Inelastic Collision

(Optional) Exercise 2 – Statistical Analysis

Learning Objectives

  • Measure the velocity of an object before and after a collision.
  • Determine the relationship between the momentum and kinetic energy of an object before and after an inelastic collision.
  • Determine whether kinetic energy and/or momentum is conserved during an inelastic collision

Background Information

Our goal is to determine the relationship between the kinetic energy and momentum of two objects before and after an inelastic collision. To remove friction you will use an airtrack, which is a linear track that has many holes through which air blows, suspending a sliding cart or sled. The sled moves along on a layer of air and does not actually touch the underlying track. The air-track is a one-dimensional version of the common air-hockey table, so the sled can only move in one dimension.

You will be using the Remote Web-based Science Lab (RWSL) facility in Denver, CO to perform this experiment. It is a real lab that you will access through the Internet using your computer. You will access the experiment through the RWSL Lab Scheduler in your D2L course.

Theory:

Conservation of linear momentum and energy are examined in this lab. Conservation laws are among the most important parts of physics. By definition, the value of a conserved quantity before a physical process begins is the same as the value of the conserved quantity after the process has occurred. Any physical process brings something from an initial state to a final state, and the final state can be quite different from the initial. The conservation laws give us a way of comparing these two states. That is the root of their importance inphysics.

The conservation of linear momentum of an isolated system is a core law of physics. The total momentum of a system before a collision is always equal to the final total momentum, since the system of colliding objects can be considered as isolated during the collision. External influences are negligible compared to the strength of the interaction between the colliding bodies during the collision, and the short duration of the collision.

You will examine inelastic collisions in this lab activity. Elastic collisions conserve the kinetic energy of the system as well as momentum. A completely (or perfectly) inelastic collision, in which the two objects stick together, is a special case that will be considered. The kinetic energy of the system is not conserved during an inelastic collision.

Equipment

  • Paper
  • Pencil/pen
  • Computer (access to remote laboratory)

Preparing to Use the Remote Web-based Science Lab (RWSL)

Click on this link to access the Installguide for the RWSL:

Follow all the directions on this webpage to get your computer ready for connecting to the remote lab.

Introduction to the Remote Equipment and Control Panel

Watch this short tutorial video to see how to use the RWSL control panel:

There are appendices at the end of this document that you can refer to during your lab if you need to remind yourself how to accomplish some of the tasks using the RWSL control panel.

Pre-Lab Questions:

  1. The combined sleds after the collision will have a velocity that is ______than the single moving sled before the collision. Explain why this is so.
  1. The combined sleds after the collision will have a momentum that is ______than the single moving sled before the collision. Explain why this is so.
  1. The combined sleds after the collision will have a kinetic energy that is ______than the single moving sled before the collision. Explain why this is so.
  1. A more massive sled combination(after the collision) will have a ______(faster/slower) final velocity than a less massive sled combination.Explain why this is so.
  1. A more massive sled combination (after the collision) will have a ______(higher/lower) final kinetic eneryg than a less massive sled combination. Explain why this is so.

Experimental Procedure:

Read and understand these instructions BEFORE starting the actual lab procedure and collecting data. Feel free to “play around” a little bit and explore the capabilities of the equipment before you start the actual procedure.

Summary of Experimental Procedure:

We will set up the experiment with one sled positioned at rest in the middle of the airtrack and one attached to an electromagnetic launcher device on the left end of the airtrack. The sled on the launcher will have a device with a wax cylinder and the other one will have a device with a needle on it that will cause the two sleds to stick together when they collide, as shown in the two images below.

Photogates 1 and 2 will be used to measure the velocity of the sled that is launched and photogates 3 and 4 will be used to measure the velocity of the two sleds after the collision.

InstantaneousVelocity Values:

The timing data display consists of the eight numerical fields labeled "Photogate 1, 2, 3, 4". The first number is the time value in seconds that has elapsed since the sled was launched and the leading edge of the flag mounted on the sled coincided with the prepositioned photogate. The second value is the time in seconds that has elapsed since the leading edge of the flag initiated the signal and the trailing edge interrupted the signal. Thus, the time between these two values is how long it takes the flag on the sled (length = 10.0 cm) to pass through one photogate. This way, we can measure the instantaneous velocity as the sled passes through each photogate.

Exercise 1 – Kinetic Energy and Momentum in an Inelastic Collision

For all steps involving moving sleds, use the robot arm, if available, or ask the Lab Technician to assist you.

Data Collection

  1. Ask the Lab Technician to ensure that the launcher attachment is installed on the electromagnet.
  2. Using the robot arm (if available), or asking the Lab Technician to assist, place each sled onto the electronic scale and determine the mass.
  3. Ensure that the air pump is turned on, and place the sled with the needle in the middle of the air track.
  4. Click the gray “Click to Capture Sled” button energize the electromagnet.
  5. Place the other sled onto the airtrack and load it onto the launcher.
  6. Make sure Trial Number 1 is selected on the Controls tab, and click the green “Click to Launch Sled” button.
  7. Select the Data tab and make sure the data table fills in for Trial 1. Write down these numbers to analyze at a later time.
  8. Return to the Controls tab and increment the Trial Number so you don’t over-write your previous data.
  9. Repeat steps 3 through 8to get a total of ten runs. Rotate control of the control panel to allow each student in your group to collect at least one set of data. You can collect more data than this if you want to and have time.
  10. Repeat the process to collect 10 runs using a more massive sled.
  11. Record all data in an appropriate table in your notebook or on your computer.

Analysis (can be done after your lab period if you run out of time):

  1. Prepare a data table in Excel and enter all the times from your 10 runs of data.
  2. Remember that photogates 1 and 2 are for the launched sled, and photogates 3 and 4 are for the combined sleds after the inelastic collision.
  3. From your ten data sets, calculate the average velocity of the single sled before the collision, and the average velocity of the combined sleds after the collision.
  4. Use the masses and velocities you determined to calculate the momentum and energy of the sleds before and after the collision.
  5. Record all your data in an appropriate table.

Post Exercise Questions:

  1. How did the velocity of the combined sleds compare with the velocity of the single sled?
  1. Was momentum conserved in the collision?
  2. What evidence supports your conclusion?
  1. Was kinetic energy conserved in the collision?
  2. What evidence supports your conclusion?
  1. Did the results of this experiment agree with your expectations or not? Explain.

(Optional) Exercise 2– Statistical Analysis

Calculate the velocity of the single and combined sleds for each of the 10 data sets.

  1. Was the velocity of the combined sleds statistically the same or different than the velocity of the single sled? (present statistical calculations to support your answer)
  2. Quantify the experimental error in the average velocity for the single sled and for the combined sleds. (present statistical calculations to support your answer)

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