Summary
In this lesson, students will explore the conservation of mechanical energy and how it relates to work during collisions. They will activate prior knowledge using the How I Know It strategy to review key vocabulary such as potential energy, kinetic energy, and work. In groups, students will follow a guided investigation using marbles and toy cars to test their hypotheses. They will graph their data and apply their understanding to a real-world collision scenario.
Essential Question(s)
What effect does increasing the potential energy of an object have on the work it does on another object during a collision?
Snapshot
Engage
Students are challenged to list as many things that they already know about potential energy, kinetic energy, and work.
Explore
Students make a hypothesis based on the essential question and carry out a structured investigation to test it.
Explain
Students state their hypotheses, explain the investigation, and state their conclusions.
Extend
Students calculate the amount of force applied to the car and create graphs that shows the effect of increasing potential energy on the force applied to the car and the distance it traveled.
Evaluate
Students are given a scenario of a car involved in a rear collision. Students will figure out how far the car will travel and if a nearby pedestrian is in danger.
Materials
Lesson slides (attached)
Lab Investigation handout (attached; stapled; one per student)
Toy car (one per group)
Ruler (one per group)
Meter stick (one per group)
Marbles (five marbles per group)
Books for stacking
Electronic scale(s)
Graph paper (one per student)
Calculator (one per student or group)
Sticky notes (one per student)
Preparation
Exploration Prep
To ensure the challenge works properly, make sure the ruler has a groove or track for the marbles to roll down smoothly. Also, check that the toy cars are in good condition and roll straight without veering off course.
Prior Knowledge
They will need a prior knowledge of the three equations:
PE = mgh
KE = 1/2 mv²
W=Fd
Consider unhiding slide 6 if students need a review.
Engage
10 Minute(s)
Use the attached Lesson Slides to guide the lesson. Introduce the lesson using slide 2.
Display slide 3 and have students work in pairs. Point out the terms on the slide: potential energy, kinetic energy, and work. Explain that they will use the How I Know It instructional strategy to write everything they know about these terms and how they know it. Pass out the Lab Investigation handout to each student. Direct them to the first page. Encourage them to think back to previous science classes, activities, and experiments for their response.
The How I Know It strategy requires the students to think deeply about how they know the terms. If students can't really think how they know or remember these terms, lead a class discussion and start drawing those experiences and knowledge out as a group.
Explore
50 Minute(s)
Display slide 4 and share the essential question: “What effect does increasing the potential energy of an object have on the work that is done on another object during a collision?”
Instruct groups to collaborate for a few minutes and write a one-sentence hypothesis on their handouts. Allow groups to share their hypotheses.
Display slide 5 and go over the lesson objectives with the class.
Show students the following materials: five marbles, a toy car, a ruler, a meter stick, books for stacking, and an electronic scale.
Display slide 7. Inform the students that they will use the materials to complete an investigation that will test their hypotheses and answer the essential question. Make sure the students know to gather quantitative data. Put students into groups of 2–4 students.
Display slide 8 and have students refer to the next section of their handout. Instruct each group to make a list of all the variables that can be measured when potential energy, kinetic energy, and work are involved. Also encourage them to make a list of variables they should keep constant.
Display slide 9. Inform students they will be creating a ramp from the ruler and rolling marbles down the ramp to collide with the toy car. They will repeat this investigation with 1, 2, 3, 4, and 5 marbles. Have students follow the steps for Procedure A on their handout and record the results in the data table. Students will need to answer the questions on the handout after they have completed the investigation.
Explain
25 Minute(s)
Display slide 10 and introduce the 3-2-1 instructional strategy and have each group record three things they learned from their investigation, two questions they have, and one thing they found interesting on their handout. Have volunteers share with the class what they recorded.
Direct students to the next section on their handout. Explain any sources of error for the experiment and address parts of the procedure that could be refined.
Display slide 11 and discuss the following question as a class: “In this investigation, how does potential energy eventually become the work that is applied to the second car?”
Call on volunteers to answer and explain their reasoning to the question.
Extend
30 Minute(s)
Display slide 12 and instruct students to calculate the potential energy of each of their trials. Direct students to the first analysis of their handout. Pass out a calculator to each student or each group.
Display slide 13, ask the students the following question: “Assuming that all the potential energy is gone at the bottom of the ramp, what is the kinetic energy the car possesses?” (The answer is equal to the initial potential energy.) Pause and allow students to respond.
Next ask the students the next question: “Assuming that all of the kinetic energy becomes work done on the second car, what force was placed on the second car?” Pause and let students respond.
Instruct students to calculate the force of the car as the potential energy increases.
Display slide 14. Now students are ready to create the graphs. Have them graph the increasing potential energy vs. the force applied on the car and the distance the car traveled. Students will need two y-axis (one on left and one on right, labeled force and distance respectively), and the potential energy will be on the x-axis. Provide students time to work on their graphs.
Once the students have finished their graphs, discuss the trends they notice in the graph. Consider reviewing independent and dependent variables.
Ask students to separate from their groups so they can work individually for the Evaluate section of the lesson.
Evaluate
10 Minute(s)
Display slide 15. Read the students the following scenario: “You are sitting at a stoplight at the bottom of a hill. A car at the top of the hill has brake failure. It is freely rolling down the hill and will collide with the rear of your car. The car is 1245 kg (similar to yours), the height of the hill is 155 m and it collides with your car applying 3255 N of force. A woman is pushing a stroller 600 m in front of you. When your car lurches forward, will it strike the woman and the stroller?”
Have students complete an Exit Ticket. Give students a sticky note and instruct them to write yes or no (indicating “yes, it will hit her” or “no, it will not”), followed by the distance their car will travel. Have them stick the note to your door on the way out. Make sure they put their name on the note.
Resources
The Physics Classroom. (2009). Marble energy lab: teacher’s guide. https://www.physicsclassroom.com/getattachment/lab/energy/e4tg.pdf
K20 Center. (n.d.). 3-2-1. Strategies. https://learn.k20center.ou.edu/strategy/117
K20 Center. (n.d.). Bell ringers and exit tickets. Strategies. https://learn.k20center.ou.edu/strategy/125
K20 Center. (n.d.). How I know it. Strategies. https://learn.k20center.ou.edu/strategy/144