“CRASH COURSE” ACTIVITY

Momentum Bashing II

Crash Course
Definitions
speed: how fast something moves, calculated by dividing distance traveled by time of travel
velocity: the speed of an object and its direction of motion
variable:any factor that can be controlled, changed, or measuredin an experiment

Key question(s)

  • Does increasing an object’s velocity increase its momentum?
  • What determines if one vehicle has more momentum than another in a

two-vehicle collision?

Grade levels:6-12

Time required: 40 -50 minutes

Objectives

Students will:

  • conduct an investigation to provide evidence that increasing an object's velocity increases its momentum.
  • organize investigation data to complete a data table.
  • construct and interpret graphical displays of data to describe the relationship of the velocity of an object to its momentum.
  • evaluate the investigation’s design to provide evidence that a revised procedure produced more reliable results.
  • explain what determines if one vehicle has more momentum than another in a two-vehicle collision.

Next Generation Science Standards

Disciplinary Core Ideas

  • HS-PS2 Motion and Stability: Forces and Interactions
  • MS-PS2 Motion and Stability: Forces and Interactions

Science and Engineering Practices

  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Background information

See Activities #2 and #4 for background information on momentum. In this activity, students are challenged to revise Student Activity#2 Momentum Bashing to investigate how an object’s speed affects its momentum. They are also challenged to think like scientists and engineers as they revise the procedure to address design flaws they identified in Activity 2’s Analysis Questions 2, 3, and 4. In this guided-inquiry lesson, students are given bullet points to help them write their procedure, construct a data table, and plot a graph. Students are also asked to identify the investigation’s independent, dependent, and controlled variables. An independent variable is a variable that is deliberately changed by the experimenter (i.e., increasing the starting height of the ruler thereby increasing the speed of marble). The dependent variable is the variable that changes in response to the independent variable (i.e., distance the cup moves after it is hit by the marble). Controlled variables are other variables that could potentially affect the dependent variable but are kept from doing so by the investigator (i.e., size of the marble, length of the ramp, and/or size of the cup).

Speed and velocity are often used interchangeably. However, scientists and engineers distinguish between the two. Velocity is the speed of the object and the direction it is traveling (i.e., 30 km/hr, east). This distinction only becomes important when the direction of motion is a concern or changes.

Materials needed

For each group:

  • ruler with center groove (1)
  • marble (1)
  • 5-ounce (148 ml) paper cup (1)
  • scissors (1)
  • meter sticks, metric measuring tapes, or rulers (2)
  • books or papers to support track (from 1-4 cm height)
  • notebook paper (3-4 sheets)
  • graph paper

Procedure

These mental habits encourage the practice of critical and creative thinking as well as ethical behavior.
  1. Ask for volunteers to describe unexpected problems or unusual events that possibly occurred during their previous investigation on momentum (Activity 2 – Momentum Bashing). For example: when using multiple marbles to investigate how increased mass affected an object’s momentum many students discovered several of the marbles spun out of the cup during impact thereby decreasing the overall momentum transferred to the cup. Ask students to describe how the marbles spinning out of the cup effected their data (i.e., Even though the overall distance the cup moved increased with each marble added, the distance gained when adding the fourth marble was not as much as the previous trials with two or three marbles).
  1. Encourage students to think like scientists and engineers (see sidebar) as they redesign their new and improved procedure. Scientists and engineers try to develop and maintain these mental attitudes as they apply their process skills to investigate real-world questions. In the prior activity, the momentum was increased in each trial by adding another marble. Although it worked, some of the marbles spun out of the cup during their collision with the cup thereby reducing the overall momenta transferred to the cup. Ask students to propose other methods that may possibly increase the marble’s momentum other than by increasing its mass. Without giving away the answer, help students realize increasing the marble’s velocity is a viable option to try in the next investigation.
  1. Writing a procedure:Using the Procedure’s bullet points on the Act 5 Student Activity sheet, guide students through the process of redesigning the Act 2 – Momentum Bashing procedure to investigate if increasing a marble’s velocity increases its momentum. Raising the starting height of the ruler increases the marble’s velocity. Students should raise the ruler in equal increments (i.e., increase the height in 2.0 cm increments). Help students identify and operationally define (how they intend to directly or indirectly measure) the variables in the investigation:
  2. Independent variable – marble’s starting height, measured in centimeters (cm)
  3. Dependent variable – distance cup moves, measured in centimeters (cm)
  4. Controlled variables – for each trial: increase ruler height in equal increments; use same size marble, cup, and ruler; conduct on same surface
  1. Completing a data table:When recording a table of data, the measurements of the independent variable should be listed in the left-handed column and ordered from either smallest to largest or largest to smallest. See table below with sample data included.

Data table – Marble’s starting height vs Distance cup moves

Marble’s starting height
(cm) / Distance cup moves (cm) / Average distance cup moves
(cm)
Trial 1 / Trial 2 / Trial 3
2 / 7.5 / 8.0 / 8.0 / 7.7
4 / 13.5 / 14 / 13.5 / 13.7
6 / 25 / 24 / 23 / 24.0
8 / 30 / 29 / 31 / 30.0
  1. Constructing a graph:Explain that a graph is a special type of “picture” of the data that helps investigators see relationships between the independent and dependent variables. Have students construct their graphs following the four guidelines listed on their sheet. Review the following rules for constructing a best-fit line for a set of data points:
  2. The line should be a straight line or smooth curve.
  3. All points should lie either on the line or near the line.
  4. For the points near the line, there should be approximately equal number of points on either side of the line. A proper best-fit line should average out the points on the graph. In the examples below, the straight-line graph is the better choice since more points lie on the line.

Examples of best-fit lines:

(see next page)

Using a straight line:

Using a smooth curve

Answers to Analysis Questions:

  1. Describe the relationship between the starting height of marble and the distance the cup moved?

Ask students to describe the relationship between the variables on the graph. The general method for describing the relationship between variables on a graph is to state what happens to the dependent variable as the independent variable changes. For the above graphs, a statement of relationship might read: “The distance the cup moves increases as the starting height of the marble increases.”

  1. Do you believe your revised procedure produced more reliable results? Defend your answer with evidence derived from your data table.

Ask students to share their observations and if theirrevised procedure produced more reliable results. Encourage students to defend their answers with evidence derived from their data table. For example, “Trial results were more consistent. At the 4cm marble starting height the trial results had only a 0.5 cm variation with Trial 1 at 13.5 cm, Trial 2 at 14 cm, and Trial 3 at 13.5 cm.”

  1. How is the marble’s starting height related to the marble’s final velocity before impacting the cup?

Increasing the marble’s starting height increases its final velocity. Explain that increasing the marble’s starting height increases it energy of position or potential energy (PE). As the marble rolls down the ruler most of the PE is converted to energy of motion or kinetic energy (KE).

  1. Explain how the marble’s final velocity affects its momentum?

Increasing the marble’s final speed directly increases its momentum. Momentum is the product of an object’s mass multiplied by its velocity. Momentum = mass x velocity

Answer to Crash Question

  1. What determines if one vehicle has more momentum than another in a two-vehicle collision?

Momentum is calculated by multiplying the car’s total mass (including occupants and cargo) times the car’s velocity before impact. The equation is momentum = mass x velocity (p=mv). Given this equation, it is possible for a less massive car that is traveling very fast to have a greater momentum than a more massive car traveling at a slower speed.

Extension(s)

  1. Have students discover the Law of Conservation of Momentum by exploring the results of two colliding objects in Activity #4 – Conservation: It’s the Law.
  2. Ask students to visit the IIHS website (iihs.org) and search “mini-vs.-midsize show weight is key” Have students read the report explain how car size and weight are crucial to protecting people in crashes.

Understanding Car Crashes Video

Momentum Bashing II

Crash test question(s)

  • Does increasing an object’s velocity increase its momentum?
  • What determines if one vehicle has more momentum than another in a two-vehicle collision?

Purpose

  • To determine if increasing velocity increases momentum
  • To conduct a guided-inquiry investigation

Materials needed

For each group:

  • ruler with center groove (1)
  • marble (1)
  • 5-ounce (148 ml) paper cup (1)
  • scissors(1)
  • meter sticks, metric measuring tapes, or rulers (2)
  • books or papers to support track
  • notebook paper (3-4 sheets)
  • graph paper

Discussion

During Activity #2 - Momentum Bashing, you investigated the effect of an object’s mass on its momentum. However during the investigation, you identified flaws in the investigation’s design. When you rolled three or four marbles into the cup they often caused the cup to spin thereby allowing marbles to escape. Now, you will revise the investigation’s design to fix that flaw while also determining if increasing a marble’s velocity increases its momentum.

Procedure

It’s your turn to write the procedure. On a separate sheet of paper, revise the procedure using the materials listed above to investigate if increasing a marble’s velocity increases its momentum. Include the following in your procedure:

  • Number the steps in your procedure.
  • Describe your procedure in enough detail that another group could follow it.
  • Draw pictures to help show important steps in the procedure.
  • Identify your independent and dependent variables.
  • Identify your controlled variables. (Controlled variables are variables that could change the dependent variable but are kept from doing so by you. The more variables you control the more reliable your results. Try to control at least three.)

Data table

Following the three guidelines listed below, organize your data in the table below.

  • Sequentially order your independent variable data.
  • Clearly label each column.
  • Include units of measurement for each variable.

Graph

Following the four guidelines listed below, plot your data on the graph paper provided.

  • Make the graph large.
  • Title the graph and label both axes.
  • Place the independent variable on the x-axis and the dependent variable on the y-axis.
  • Draw a best-fit line using a smooth curve or a straight line.

Analysis

  1. Describe the relationship between the starting height of marble and the distance the cup moved?

______

______

  1. Do you believe your revised procedure produced more reliable results? Defend your answer with evidence derived from your data table.

______

______

  1. How is the marble’s starting height related to the marble’s final velocity before impacting the cup?

______

______

  1. Explain how the marble’s final velocity affects its momentum?

______

______

Crash Question

  1. What determines if one vehicle has more momentum than another in a two-vehicle collision

______

______

Understanding Car Crashes Video