Lab 9: Human Power

Purpose:         To determine the power output of a person.

Equipment:    Two meter meter-sticks, stopwatch, and kilogram bathroom scale.

Introduction: Power is defined to be the rate at which work is done or equivalently, the rate at which energy is converted from one form to another. In this experiment you will do some work by climbing from the first floor of the science building to the second floor. By measuring the vertical height climbed and knowing you mass, the change in your gravitational potential energy can be found:

 △PE = mgh

        Where m is the mass, g the acceleration of gravity, and h is the vertical height gained.

         Your power output can be determined by

Power = △PE / △t   where △t is the time to climb the vertical height h.

Procedure:  We started this lab by recording our weight, which we then multiplied by g (9.8) to calculate for N. We measured the vertical distance between the ground floor and the second floor of the science building. The person keeping the time record for the class would time each persons running, or walking up the stairs. We did two trials. We then calculated our personal power output in watts using the data collected. We then determined our average power output in units of horsepower. Finally we added our average power on the board to calculate the average power of the entire class.

Data: 

 h = 4.26 m

mg = 860 N

t1= 8.25 s

t2= 8.16 s

Avg t = 8.21 s

△PE = mgh 

(860 kg*m/s^2) (4.26 m)

= 3,663. 6 kg*m^2/s^2

Power = △PE / △t

(3,663. 6 kg*m^2/s^2) / 8.21 s

= 446.24 W (1 Hp/ 746 W)

= .60 Hp

Questions: 1. Is it okay to use your hands and arms on the hand railing to assist you in your  

                       climb up the stairs? Explain why or why not.

                                 - Using the hand railing to assist is in going up the stairs is fine since it does not affect or change either your mass, the force of gravity or the height.

                   2. Discuss some of the problems with the accuracy of this experiment.

                              - A problem with accuracy might come from our measurements in height since it might be hard to get an accurate reading using only meter-sticks to measure. Our measurements for our weight and time might also not be as accurate as we might have wanted them to be.

  Conclusion: In this lab we learned about potential energy and power, and how potential energy could be defined as the energy that is within an object. Gravity gives the object its potential energy, which could be used to do work. Which is shown in our equation of PE = mgh. Power on the other hand is the rate at which the energy is used. Our equation for power shows us that while the same amount of work might be performed, if the change in time decreases more power is used, if the time increases then less power is used.