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Content Teaching Academy 2014
James Madison University
Intermediate Physics-Graduate Credit
Lesson Plan 1
Lesson Plan
Teacher Name: Ms. Kristen Roscoe
Unit: 5-Net Force
Lesson Title: Elevator Lab/Introduction to Net Force
Instructional Goals:
The amount by which the forces acting on an object are unbalanced is called the
net force.
When the forces acting on an object are unbalanced, the object will accelerate.
Because acceleration is a change in velocity, and velocity includes both speed and
direction, a net force will change the speed and/or the direction of an object's
motion.
Newton's 2nd Law:
The acceleration of an object is directly proportional to the net force acting on it
F
and inversely proportional to its mass, a µ . For convenience, this is usually
m
expressed as Fnet = ma.
Force is measured in units of Newtons. One Newton of net force on a onekilogram object produces an acceleration of 1 m/s2. Therefore, a Newton is the
same as a kilogram*meter/second2. (N = kgm/s2)
Solve quantitative problems involving forces, mass and acceleration using
Newton's 2nd Law.
a. use force diagram analysis to find the net (unbalanced) amount of force.
b. list known and unknown force and motion variables
Virginia Standards of Learning:
PH.5
The student will investigate and understand the interrelationships among mass, distance,
force, and time through mathematical and experimental processes. Key concepts include
a) linear motion;
b) uniform circular motion;
c) projectile motion;
d) Newton’s laws of motion;
e) gravitation;
f) planetary motion; and
g) work, power, and energy.
Objectives: SWBAT
Draw the force diagram for a person on a scale in an elevator
Label the direction of the net force and the acceleration on an object under
different scenarios
Calculate the net force and the acceleration on a person while the elevator moves
upward
Calculate the net force and the acceleration on a person while the elevator moves
downward
Calculate the net force and the acceleration on a person while the elevator is at
rest.
Evaluation: Elevator Lab and Worksheet 2
Materials:
Scale
Elevator
Lab Handout
Whiteboards
Markers
Erasers
SMART Notebook
Worksheet 2
Procedures:
Hand out elevator lab sheet and complete: Students will complete an
introductory lab on Newton’s second law concepts and problems. Students will
analyze changes to the force of gravity on an object as an elevator travels up and
down. Students will answer preliminary lab questions then in small groups
complete the lab.
Whiteboard elevator lab: Once a group has completed the lab, they will answer
all of the questions and then whiteboard their results. Once all groups are finished,
we will have a whiteboard discussion as a class.
Notes Newton’s Second Law: Students will complete notes on Newton’s second
law, which states that net force on an object is equal to the mass of the object
multiplied by the acceleration of the object. The net force comes from the sum of
all of the forces acting on the object in all directions. In the last unit, the students
focused on balanced forces, where the net force on the object was zero meaning
that the object was either moving at a constant speed or was at rest. Now, the
students will focus on objects that are experiencing unbalanced forces. We will
use the results from the elevator lab
Homework-Worksheet 2: For homework, students will complete worksheet 2 on
Newton’s 2nd Law problems.
Assignments: Worksheet 2
Name
Date
Pd
Net Force Particle Model:
Elevator Lab
In today's activity you will look at how the forces change on you as you ride in an
elevator.
Prep: Read the following questions before going over to the elevator, and note the
observations you need to make:
1. At what times in the motion of the elevator does the bathroom scale show your weight
(or the weight of the person standing on the scale)?
Make a mental note of the scale reading.
2. At what times in the motion does the scale show a value greater than your weight?
Make a mental note of the scale reading.
3. At what times in the motion does the scale show a value less than your weight?
Make a mental note of the scale reading.
Experiment: Take the bathroom scales with you and take a ride in the elevator. Have
someone stand on the bathroom scale that doesn't mind revealing his or her weight to
others. Observe and remember the forces for numbers 1, 2 and 3 above.
Data/Observations: When you return to the classroom record your observations.
Force in pounds
Force in Newtons (1 pound = 4.5
Newtons)
Scale reading at rest:
_______________
_______________
Maximum scale reading:
_______________
_______________
Minimum scale reading:
_______________
_______________
Label the following as equal to, greater than, or less than the scale reading at rest.
_____________ At rest at the bottom
_____________ Starting to go up
_____________ Going up at constant speed
_____________ Slowing to stop at the top
_____________ Stopped at the top
_____________ Starting to go down
_____________ Going down at constant speed.
_____________ Slowing to stop at the bottom.
Calculate the mass of the person on the scale in kilograms: _____________________
Force Analysis: Draw a quantitative force diagram for the passenger in each of the
following situations during the elevator ride. Label the forces in Newtons. To the right of
each diagram draw a velocity and acceleration vector that describes the motion of person
in the elevator. Calculate the net force and the acceleration of the person.
1. At rest at the bottom
Quantitative force diagram
2. Starting to go up
Quantitative force diagram
velocity vector:
velocity vector:
acceleration vector:
acceleration vector:
net force =
net force =
acceleration =
acceleration =
3. Going up at constant speed
Quantitative force diagram
4. Slowing to stop at the top
Quantitative force diagram
velocity vector:
velocity vector:
acceleration vector:
acceleration vector:
net force =
net force =
acceleration =
acceleration =
5. Stopped at the top
Quantitative force diagram
6. Starting to go down
Quantitative force diagram
velocity vector:
velocity vector:
acceleration vector:
acceleration vector:
net force =
net force =
acceleration =
acceleration =
7. Going down at constant speed.
Quantitative force diagram
8. Slowing to stop at the bottom.
Quantitative force diagram
velocity vector:
velocity vector:
acceleration vector:
acceleration vector:
net force =
net force =
acceleration =
acceleration =
9. How do the upward accelerations compare to the downward accelerations?
Explain why.
Name
Date
Pd
Net Force Particle Model Worksheet 2:
Newton's 2nd Law
1. A 4600 kg helicopter accelerates upward at 2.0 m/s2. Determine the lift force exerted
on the propellers by the air. Make a quantitative force diagram. Write a net force
equation for the axis along which forces are not balanced.
2. The maximum force that a grocery bag can withstand without ripping is 250 N.
Suppose that the bag is filled with 20 kg of groceries and lifted with an acceleration
of 5.0 m/s2. Do the groceries stay in the bag? Make a quantitative force diagram.
Write a net force equation for the axis along which forces are not balanced.
3. A student, standing on a scale in an elevator at rest, sees that his weight is 840 N.
As the elevator rises, the scale reading increases to 1050 N, then returns to normal.
When the elevator slows to a stop at the 10th floor, the scale reading drops to 588 N,
then returns to normal. Draw a motion map for the student during his elevator ride.
Determine the acceleration at the beginning and end of the trip. Make quantitative
force diagrams. Write a net force equation for the axis along which forces are
not balanced.
4. A sign in an elevator states that the maximum occupancy is 20 persons. Suppose that
the safety engineers assume the mass of the average rider is 75 kg. The elevator itself
has a mass of 500 kg. The cable supporting the elevator can tolerate a maximum force
of 30, 000 N. What is the greatest acceleration that the elevator's motor can produce
without snapping the cable? Make a quantitative force diagram. Write a net force
equation for the axis along which forces are not balanced.