SelfPaced Physics Cover Sheet
Activity 3 - Energy and Power
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PHYS 1000
Self Paced
Activity 3: Energy and Power
Objective: To measure the energy and power of a student, and to witness the
exchange of energy.
Background: Physics, Concepts and Connections, Hobson, Chapter 6
Equipment and Supplies : Staircase, stopwatch, tape measure, scale, various types
of balls (tennis, racquetball, basketball, etc.)
Procedure:
(Part 1)
1) Measure the height !h of a staircase. If you used British units (feet, inches),
convert the height to meters (1 ft = 12 in, 1 in = 0.0254 m).
2) Starting from rest at the bottom of the staircase, run to the top, timing yourself.
Do this five times and find the average time. Use a precision of 1/10th of a
second.
3) Measure your weight in pounds.
4) Convert your weight in pounds to your mass in kg using the conversion
1 kg weighs 2.2 lbs.
5) Find your weight in Newtons using
w = mg
and assuming that g = 9.8 m/s2. One Newton = 1 kg m/s2.
6) Calculate the change in gravitational potential energy you experience as you
ascend the stairs: !U = mg!h. The unit of energy is the Joule (J).
1 J = 1 N m = 1 kg m2/s2.
7) Power is the rate of energy expenditure, or the work per time. For this
experiment, P = !U/ !t. Calculate your average power for your trials. The unit for
power is the Watt (W), where 1 W = 1 J/s.
8) How many 100 W light bulbs could you light?
Procedure:
(Part 2)
Measure a tennis ball’s elasticity by dropping it and measuring the height of rebound as
a fraction of the initial height. Repeat this for ten different heights. What fraction of the
initial height was transformed into thermal energy? What fraction was retrieved as
gravitational energy? Do these fractions change as a function of height? Repeat this
experiment for a different ball. Discuss your findings.
Worksheet for Activity 3: Energy and Power
1)
2)
3)
4)
5)
6)
7)
8)
9)
Height of the staircase (m)
_________.
Times:
Trial 1_____ Trial 2 ______ Trial 3_____ Trial 4 _____ Trial 5 _____
Average time (s)
_________.
Weight (lbs.)
_________.
Mass (kg)
_________.
Weight (N)
_________.
Potential energy (J)
_________.
Average power (W)
_________.
Number of light bulbs
_________.
Questions:
1) Why is it important to start from rest at the bottom of the staircase, instead of
giving yourself a running start?
Part 2)
Type of ball______________
Trial
Initial height
Final height
Fraction
retrieved as
gravitational
energy
Fraction lost
to thermal
energy
1
2
3
4
5
6
7
8
9
10
Average Fraction retrieved as Gravitational Energy __________________________
Average Fraction lost to Thermal Energy __________________________________
Type of ball______________
Trial
Initial height
Final height
Fraction
retrieved as
gravitational
energy
Fraction lost
to thermal
energy
1
2
3
4
5
6
7
8
9
10
Average Fraction retrieved as Gravitational Energy __________________________
Average Fraction lost to Thermal Energy __________________________________
Discussion: