Teacher Key (GI)

For evaluation purposes only 1

Momentum and Impulse

Guided Inquiry (GI)

Problem Statement

You walk into a lab station and you notice the group before yours has performed a lab. They left behind their data from one trial (shown to the right). Their task was to prove that the change in momentum in an object is equal to the impulse for different initial velocity values. Design and conduct an experiment to:

Recreate their lab with similar but not necessarily exact values using three different initial velocity values.

Determine a relationship between the change in momentum and the impulse of a cart rolling down an inclined track and colliding with a barrier.

Time Requirement

Preparation time 10 minutes

Pre-lab discussion and activity 10 minutes

Lab activity 45 minutes

Materials and Equipment

For each student or group:

Data collection system Dynamics track

Force sensor with bumper Dynamics track rod clamp

Motion sensor Discover Collision Bracket

Balance, (1 per class), 1200-g capacity Large base and support rod

Dynamics cart

Force (N)

Time (s)

Time (s)

25 N

Velocity (m/s)

0.75 m/s

0.75 m/s

0.60 s

0.60 s

0.66 s

0.66 s

0 N

Momentum and Impulse

For evaluation purposes only 2

Background

Vehicle airbags and the large yellow barrels full of sand called Fitch barriers near highway exits are credited with saving thousands of lives and reducing injuries to car occupants. Two important physics phenomena that occur during a collision are the change in momentum and the impulse imparted on the vehicle and its occupants.

The change in momentum can be calculated by subtracting the momentum before a collision from the momentum after a collision:

if mvmvp = (1)

Where p is the change in momentum, m is the mass, vf is the final velocity, and vi is the initial velocity.

Impulse is equal to the area under a graph of force versus time showing the force associated with the collision. Impulse I is also related to p through the impulse-momentum equation:

vmpI == (2)

Lab Preparation Although this activity requires no specific lab preparation, allow 10 minutes to assemble the equipment needed to conduct the lab

Safety Refer to the Safety section of the Instructor Information for this lab.

Design and Conduct the Experiment Write a brief outline of the procedure you will use to collect data. Identify the steps in sequence and the points at which each piece of equipment will be used. Use the following questions to guide your experiment design.

Refer to the steps outlined in the Procedure section of the Teacher Key (S) for a description of what the students' experimental design might look like.

1. Using only the equipment provided, describe how you would construct an apparatus that will measure the initial and final velocity and force associated with a cart colliding with a barrier.

Answer provided here.

2. How will you configure your data collection system to display your measured values? What sort of a display (graph, table, et cetera) will you use for each and why?

Answer provided here.

Teacher Key (GI)

For evaluation purposes only 3

3. The force sensor has a zero function that sets the initial measured force to zero whenever it is pressed. Do you think it would be good practice to press this button before each of your trials? Why or why not?

It would be good practice to press this before each trial so that all of our values are consistent.

4. When making measurements, in what order should the following events occur?(Number them in the correct sequence.)

___x___ Release the cart.

___x___ Begin data collection

___x___ Stop data collection.

___x___ The cart collides with the barrier.

5. At what points in your display showing the velocity of the cart should the initial and final velocities be measured?

Answer provided here.

6. What technique will you use to measure the impulse associated with the collision?

Answer provided here.

Diagram of the Experiment

Draw a diagram of the experimental setup you will use. Be sure to label each component and the measurements each component will be used to make. In the diagram, include components that were used but did not make any measurements.

Refer to the Set Up section of the Teacher Key (S) for a diagram that should be similar to the student's diagram of the experiment.

Relevant Equations

List the relevant equations you will use and show how you will use them in conjunction with your measured values to determine the relationship between the change in momentum and the impulse of a cart colliding with a barrier.

Refer to the Relevant Equations subsection of the Background section of the Teacher Key (S).

Collect Data

Students can place their raw data in this section.

Data Analysis Present your data in the form of a table and any other way you find useful to determine the relationship between the change in momentum and the impulse of a cart colliding with a barrier.

Momentum and Impulse

For evaluation purposes only 4

Refer to the Data Analysis section in the Teacher Key (S) for examples of the data formats and data the students may include in this section.

Analysis Questions Refer to the Analysis Questions section of the Teacher Key (S) for answers.

Synthesis Questions Refer to the Synthesis Questions section of the Teacher Key (S) for answers.

Multiple Choice Questions Refer to the Multiple Choice Questions section of the Teacher Key (S) for answers.