The Arizona STEM Acceleration Project
Elevators
Elevators!
A 9-12 grade STEM lesson
Dave Wirth
Fall 2023
Notes for teachers
The purpose of this lesson is to give students an additional real life experience with Newton’s Second Law of Motion. Students will stand in an elevator and use an app on their cell phones to measure the elevator’s acceleration. They will use this acceleration in turn to find the normal force acting upon them.
List of Materials
** Would suggest that you limit the number of students in the elevator at one time to prevent expensive elevator damage.
Standards
HS.P3U1.6
Collect, analyze, and interpret data regarding the change in motion of an object or system in one dimension, to construct an explanation using Newton’s Laws. ● Newton's second law accurately predicts changes in the motion of macroscopic objects.
Standards
Creating Equations (A-CED)
A1.A-CED.A Create equations that describe numbers or relationships.
9-12.5.b. Students collect data or identify relevant data sets, use digital tools to analyze them, and represent data in various ways to facilitate problem solving and decision making.
Objective:
The students will collect data using a cell phone app and apply Newton’s Second Law of Motion to determine the normal force acting upon a person in an elevator.
Agenda
30 minutes - give example problems
5 minutes - introduce the activity
30 minutes - trip to the elevator for data collection
10 minutes - Processing time. Compare data and discuss results
Intro/Driving Question/Opening
Why does riding in an elevator feel weird sometimes? Do you sometimes feel lighter? Do you sometimes feel heavier? When do you feel heavier? Lightest? Are you actually heavier? Why?
A 60 kg person stands on a scale in an elevator at rest. Draw a force diagram for this person. What would the scale read?
Person at rest - solution
600 N
FN
FN - 600 N = 0
FN - 600 N = 0
FN = 600 N
The scale would read 600 N. This is also called the person's apparent weight. The normal force also gives the apparent weight. The normal force is how heavy you “feel”.
The same person now stands on a scale in the same elevator and accelerates upward at 3 m/s2. Draw a force diagram and find this person’s apparent weight.
Notice that since this person is accelerating
upward, this requires that the upward force is bigger
than the downward force. Notice the length of the vectors
in the force diagram.
600 N
FN
FN - 600 N = (60 kg)(3 m/s2)
FN = 780 N
The scale would read 780 N. The person’s apparent weight is 780 N and the person would feel heavier.
3 m/s2
Solution:
The same 60 kg person now accelerates downward in an elevator with acceleration -2 m/s2. Determine her apparent weight.
Solution:
600 N
FN
Since the person is accelerating downward, the downward force is greater than the upward force. Notice the magnitude of the force vectors.
FN - 600 N = ma
FN - 600 N = (60 kg)(-2 m/s2)
FN = 480 N
2 m/s2
** This person will feel lighter.
Hands-on Activity Instructions
Now it’s time to go and experience this in an elevator. You goal is to find your apparent weight in an elevator. You will be using the Phyphox app on your cell phone.
This app measures all kinds of things: sound, magnetic field, acceleration, pressure, etc.. You will be using the “Acceleration (without g)” function. You goal will be to stand in an elevator, and hold your cell phone at the correct orientation to determine the acceleration of you and the elevator.
You may want to experiment with the app for a little while before going to the elevator to determine the correct orientation of the cell phone. The cell phone measures acceleration is 3 different axes.
Once you get to the elevator, one group at a time will get in, hold the cell phone at the correct orientation, press the play button on your cell phone, and then press the elevator button. Once you get your data, press pause.
Here’s some sample data:
Lab Procedure
To collection acceleration:
1.) Get in the elevator (3-4 people)
2.) Hold the cell phone with the
correct orientation.
3.) Press the “play” button on the app.
4.) Press the elevator button.
5.) After data is collected, probably
shortly after the elevator starts
moving, press the pause button.
6.) Collect your data.
Play button
Pause button
Press “pick data” to get the acceleration at any point on the
graph.
Calculations
Once you find your acceleration, calculate your apparent weight in the elevator.
Make sure and draw a beautiful force diagram and show all work.
Explain in your own words why you feel heavier or lighter.
Assessment
1.) An 70 kg student accelerates upward in an elevator at 4 m/s2. Find her apparent weight. Draw the correct force diagram and show all work. What is the apparent weight also called?
2.) A 70 kg student stands on a scale in an elevator. He wants the scale to read 600 N in order to “meet weight” for a wrestling match. Find the acceleration of the elevator required to make this happen. Draw the correct force diagram and show all work.
Differentiation
You could have students watch this Youtube video as a review.
This is a great tutorial/activity on The Physics Classroom
Remediation
Extension/Enrichment
Have students measure their normal forces in others ways. For example, they could use their cell phone to measure their acceleration as they jump upward. They could use this acceleration and Newton’s Second Law of Motion to determine their normal force.
Ask the students to explain what happens to their apparent weight if the elevator were to accelerate downward at the acceleration of gravity. (-10 m/s2)
Solve using physics and explain conceptually.