Content Reviewed: yes
AIG Reviewed: 7/31/12
Need Revisions (Y/N): Y
Content-no
Complete: content-yes
NCDPI -- AIG Instructional Resource: Background Information
Date Submitted: 7/7/12
Great science!
Resource Title: Human Power
Subject Area/Grade Level (s):
Physics/ 9-12
Common Core/Essential Standard Addressed:
Phy.2.1.3 Explain the relationship among work, power, and energy.
Time Frame 1 hour
Additional Standards Addressed:
(integration across topics, within or across disciplines)
Phy.2.1.1 Interpret data on work and energy presented graphically and numerically.
Phy.2.1.2 Compare the concepts of potential and kinetic energy and conservation of total mechanical energy in the description of
the motion of objects.
Brief Description of Lesson/Task/Activity:
(include how this lesson/task/activity fits with a larger context)
AIGs use their knowledge of work and energy to measure the power output of the human body climbing stairs. They select a flight of stairs on
the school campus and measure the power expended to climb the stairs. To successfully complete the activity, they must have knowledge of the
Work-Energy Theorem, Potential Energy, and Kinetic Energy as well as an introduction to the concept of Power. They must also recall how
forces act on the body to do work.
Type of Differentiation for AIGs (include all that apply)
 Enrichment
 Extension
 Acceleration
Adaptations for AIGs
 Content
 Process
 Product
Explanation of How Resource is Appropriate for AIGs.
The biophysics of this activity can be intriguing to AIGs. It integrates concepts of physical conditioning, biology of muscular forces, and physics of
power. Fix this sentence: It can help think ways that physics occurs in all motion and all machines even human ones. They also like the
competition to see who has the best power production.
Needed Resources/Materials
Meter stick, stopwatch, stairs
Sources (all sources must be cited)
The idea comes from John Kolena’s Handbook for APB Physics (form the early 1990’s).
TEACHER NOTES
AIGs must dress appropriately to ensure safety. Shoes with traction are a necessity. Remind students that the rules are simple: You must start
at rest at the bottom of the stairs and end at rest at the top of the stairs.
NCDPI AIG Curriculum Resource Outline
Describe processes, steps, and materials needed at each stage of the lesson/activity.
STAGE ONE: Engage
 Hook
 Prior knowledge
 Instructional input
 Modeling
Description:
Lead a brief discussion about the forces involved in walking. Review at this point the application of Newton’s Third Law of Force. Emphasizing
the fact that Action-Reaction Pairs of forces act on different objects and do not ever cancel each other figures prominently in the movement of
objects. It is an important idea that even AIGs must be reminded of throughout the study of physics. After developing a student-generated list
of possible forces acting on a person climbing the stairs (friction, normal force, gravity or weight), ask students to draw the free body diagram
and to share with each other their results.
STAGE TWO: ELABORATE
 Guided and independent practice
 Guiding questions
Description: Use the pre-lab questions in the activity to set the stage for the activity. Allow students to compare answers and discuss
conclusions. Possible answers are given below. After discussion, complete the activity.
1. In the space at the right, construct a free-body diagram showing all the forces acting upon you as you climb up stairs at a constant speed.
Please label all forces.
Legend: Red is Normal Force
Blue is Static Friction
Green is Force of Gravity or Weight
2. Write an equation for the work done on your own body by gravity as you climb the stairs (2.2 pounds of weight is equivalent to 1.0 kg of mass
or 9.8 Newtons of Weight). Work by Gravity = Mg h = (Weight in lbs/2.2) x 9.8 x total height to climb
3. If you start at rest and finish at rest, then the work-energy theorem states that the net work done by all forces equals __Zero__________
Note: net work = change in Kinetic Energy = 0-0 (Start at rest and end at rest)
STAGE THREE: EVALUATE
Assessment
Description: Use the Post Lab Questions to assess understanding. Also discuss, what professions/specialties/hobbies need to be able to use
this information? Why?
1. A ski lift delivers two skiers to the top of a 400-meter tall hill every 10 s. The mass of a skier plus equipment is 90 kg. Assuming
dissipative force is negligible (no kinetic friction), determine the power output of the chair lift motor.
Answer: {(90 x 2) x 9.8 x 400} Joules/ 10 sec = 7056 Watts
2. A rock climber elevates her 55-kg body a height of 20 meters in 8 minutes. Determine her power output in Watts.
Answer: (55 x 9.8 x 20 Joules)/ (8 x 60 sec) = 22.5 W
3. An elevator motor produces 1000 W. How fast (in m/s) can it lift a 500-kg load?
Answer: Power = Force x Velocity so velocity = Power/ Force= 1000 W/ (500 x 9.8 N)= 0.204 m/s
4. The rate at which a person can do work is dependent upon a number of different physiological properties. But it is true that there is a
connection between body mass and power (up to a certain point). For example, a person does work at of 10.0 Watts/kg during sustained
activity. Given this value, how fast (in m/s) can he run up stairs at a constant speed?
Answer: Power = mgh/t so that Power/mass = g x h/t = g x speed. That means that that speed = (Power/mass)/g = 1.02 m/s
5. A car must do work at a rate of 5 kW to maintain a constant speed of 10 m/s on flat ground. How large are the forces opposing its
motion?
Answer: Power = Work / time = (Force x distance) time = Force x (distance/ time) = Force x speed. Solve for force: 5000= F x 10 so that F= 500 N.
TEACHER NOTES:
Once again, make sure that students start at rest at the bottom of the steps and end at rest at the top of the steps. If they do not then disqualify
that result. If outdoor stairs are available then that is a perfect place for this activity. Anyone without closed toed shoes should not take part in
this activity. That is a safety precaution.