Free Fall on Planet Newtonia
Lesson 9 of 14
Objective: Students will be able to state the value of the acceleration due to gravity in meters per second squared and use it in mathematical models of free fall.
The goal of this lesson is to give students more experience and practice with free fall problems not only on Earth, with an acceleration of gravity of 9.8 meters per second squared, but also on other planets. Most of this lesson focuses on how to calculate different values, like acceleration, time, velocity or displacement, of an object in free fall using acceleration due to gravity.
To start off class, I have students self-assess on the Career and College Readiness Skill standards that we created Looks Like, Sounds Like charts for at the beginning of the year. My school is beginning to assess all students on College and Career Readiness Standards. These include: Respect, Collaboration, Time Management and Habits of Success. Teachers are expected to evaluate students on these standards every 4 weeks. I decided that it would also be good for students to do a self-assessment every 2 weeks.
I give students a form where they rate themselves on a scale of 1-4, 1 being concerned and 4 meaning great work. I also have them write about their strengths and what they can do to improve in the future. Students have 5 minutes to read through the criteria and assess themselves. After they turn this in, I make my own rating for each student on their charts for each skill. On Monday students see how their self-assessment compares to mine. I do this activity to make students aware of and reflect on their own behaviors in the classroom.
Free Fall on Planet Newtonia
After students have finished assessing their behavior in class, I ask them to take out their packets and turn to Free Fall on Planet Newtonia. I use this worksheet because it helps students see another way to find the acceleration due to gravity. When I do this worksheet, I help students to go through it so we do this worksheet more as guided notes than a worksheet on their own.
To start out this worksheet, I read through the instructions and direct students to the picture on the back of the worksheet that shows the ball falling. Then we start going through the questions on the worksheet starting with the average velocity between points A and E. I ask students if they remember the equation for velocity from the previous unit and at least one student will volunteer the equation velocity = change in position/time. So I walk students through the first calculation to find that the average velocity is 0.05 m/s, first finding the distance between A and E measuring with a ruler. Then, I allow students to find the average velocity between points A and C on their own.
After students have found the average velocity between points A and C to be 0.04 m/s, I ask them what the difference between average velocity and instantaneous velocity is. Instantaneous velocity is velocity at one point in time, so we look at the next question that asks what the instantaneous velocity is at point B. Since we did not focus on this point much in Unit 1, I explain that the instantaneous velocity at a midpoint (point B) is equal to the average velocity of the entire section (between points A and C). So the answer that they got for #2 is also the answer to #3.
Since students have had a little more exposure and practice with the average vs. instantaneous velocity concept, I let them find the next two problems as a Think-Pair-Share. To complete a Think-Pair-Share, I ask students to try to complete the questions on their own for about 2 minutes. Then, I ask them to compare with a partner and eventually students share out their answer with the class. Once we have made sure that each student has the same answer, we move on to calculate the acceleration on planet Newtonia. I ask students to remind me of the acceleration equation which is acceleration = change in velocity/time. I ask them how we can find the change in velocity and they determine that we can use the change in the instantaneous velocities at B and D divided by the time that elapsed to get an acceleration of 0.01 meters per second squared. One student's work is shown in Planet Newtonia Student Work.
After we have finished the worksheet, I ask my students how this compares to Earth. I want students to understand that planet Newtonia has less acceleration due to gravity so that means that there is not as great of a pull toward the planet as on Earth. I also want students to look closely at the picture and I ask them how they know it is accelerating. Most students are able to see that the distances get greater each second so the ball must be accelerating. I tell them that this is important when we talk about free fall that they understand that each second an object falls in falls a greater distance.
Free Fall Worksheet
After we have finished completing the Planet Newtonia worksheet, I ask students to turn to Worksheet #4 Free Fall Worksheet in their packets. At the top of the page, I go over and write the equations that they could possibly use by asking students what we could be looking for (ex. how long?, how far?, etc.). After students have finished listing all of the possible equations to use, I remind them that in the free fall equations unless otherwise stated the acceleration due to gravity is 10 meters per second squared because the problems are occurring on the Earth.
I allow students to have some structured work time where they get to work with their groups to answer the 8 problems that are on the worksheet. As students are working, I walk around the room to assist and to make sure that students are on task. I ask students to ask their group members to help them first before asking me because I think that it is better for their peers to learn more by helping other students solve problems. I give students the rest of the period to work on the worksheet.
To end class, I remind students that whatever they did not finish is homework and we will go over it with WS #4 KEY in the next class. Then, I ask students to give me a thumbs up or thumbs down of how they feel about solving problems concerning free fall so that I can get a feel of where my students are at going into the next class.