Name:____________________
Date Submitted:__________
PHYS 1000 Activity:
Energy and Power
Background:
(Reference: Chapter 6, Physics, Concepts and Connections by Art Hobson)
Objective:
The objective of this activity is to measure the energy and power output of a person, and to
witness the exchange of energy.
Equipment and Supplies:
Part 1: Staircase with 8 or more steps, stopwatch, tape measure or meter stick and a scale.
Part 2: At least two different kinds of balls to bounce (tennis ball, basketball, golf ball, etc).
Procedure for Part 1: Power output when running up stairs
1. Measure the height of the staircase you will be running up. We will call this Δh. If you use
feet or inches you will need to convert the height to meters (1 ft = 12 in, 1 in = 0.0254 m).
Measured height
in m (Δh):
2. Start from rest at the bottom of the staircase and run to the top, timing yourself as you go.
Record the time to the nearest 0.1 seconds.
Time 1:
________
Time 2:
Time 3:
________
Time 4:
________
________
Time 5:
________
Average time
in s (Δt):
3. Measure your weight in pounds and then convert this to newtons (1 lb = 4.45 N).
Measured weight
in lbs:
________
Measured weight
in N:
4. Find your mass in kg from your weight in newtons. Recall that (weight) = mg, where g = 9.8
m/s2.
Mass
in kg (m):
1
5. Calculate the change in gravitational energy you experience as you ascend the stairs:
Eg = mg h .
The unit of energy is the joule (J), where 1 J = 1 N m = 1 kg m2/s2.
Change in GravE
in J (ΔEg):
6. Finally, power is the rate at which energy is converted from one form to another, or the
work done per unit time. For this process,
P = Eg t .
Calculate the average power output you had for your five trials. The unit for power is the
watt (W), where 1 W = 1 J/s.
Power output
in W (P):
7. Suppose the power output you found in Question 6 is the same power you could produce
on a stationary bike, and suppose we hooked up a mechanical generator to the bike, and we
hooked up lightbulbs to the output of the generator. How many 60 W lightbulbs could you
power (simultaneously) by riding the bike as hard as you can? Would you be able to keep
them running for very long? Explain your reasoning.
8. In terms of energy, why is it important to start from rest at the bottom of the staircase,
instead of giving yourself a running start?
2
Procedure for Part 2: Comparison of elasticity
In this part you will measure the elasticity of balls. Elasticity measures how much energy is
“lost” in a collision, meaning how much kinetic energy gets transformed into thermal energy
and does not show up as kinetic energy after the collision.
Specifically you will explore whether the elasticity is affected by the height of the drop as well
as compare elasticity between two different types of balls.
Choose two different types of ball and for each one, drop it from a known height and measure
the height it rebounds to. Record the initial and final heights in the tables. Repeat this process
for ten different heights over as wide a range as you can.
Next analyze the data you collected by calculating the fraction of the initial gravitational energy
that was retrieved when the ball reached its final height. Calculate the fraction of the initial
gravitational energy that was lost to the thermal energy somewhere in the process. Record
these both in the data tables as either decimals (such as 0.56) or percents (56%). Lastly,
calculate the averages of the two fractions.
Once you have completed the data tables, answer these two questions:
9. Consider both balls. Does the fraction of gravitational energy retrieved change
systematically for different heights or is the variation just random?
10. How do the average fractions of energy retrieved/lost compare between the two balls you
used? Discuss this in a few sentences.
3
Type of ball______________
Trial
Initial height
Final height
Fraction of GravE retrieved
after bounce
Fraction of GravE “lost” to
thermal energy
Fraction of GravE retrieved
after bounce
Fraction of GravE “lost” to
thermal energy
1
2
3
4
5
6
7
8
9
10
Average of 10 trials
Type of ball______________
Trial
Initial height
Final height
1
2
3
4
5
6
7
8
9
10
Average of 10 trials
4
5
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