PHYSICS IN EVERYDAY LIFE
PHYS 110 Lab #8: Energy II
In this lab you will be prac?cing crea?ng and applying energy models for several different scenarios.
1. Happy Ball
Drop the happy ball onto the table top. We are interested in the energy of the ball from the instant you
let it go un?l the highest point it reaches aHer one bounce. We’ll also inves?gate the moment of
impact with the table.
The big idea: Applying energy models
Sketch the scenario iden?fying the system, the zero reference point, and ini?al and final points of
interest:
As the ball falls, does the gravita?onal poten?al energy increase, decrease or
stay the same?
As the ball falls, does the kine?c energy increase, decrease or stay the same?
On the way up (aHer the bounce), does the poten?al energy increase,
decrease or stay the same?
On the way up (aHer the bounce), does the kine?c energy increase, decrease
or stay the same?
What is the kine?c energy at the moment of impact with the table?
What is the gravita?onal poten?al energy at the moment of impact with the
table?
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Does the ball have some other energy at the moment of impact with the table? If yes, how do you
know and how is the ball storing the energy? [Hint: is the ball “squishy”?] If no, explain why not.
LOL diagram (ini?al drop and impact with table):
Energy Model (equa?on) (for the ini?al drop and impact with the table):
Will energy be conserved? (i.e., does ΔEsys =0?)
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Name:
Now you’ll repeat the analysis with the ini?al drop and the final height that the ball reaches.
LOL diagram (ini?al drop and final height):
Energy Model (equa?on) (for ini?al drop and final height):
Will energy be conserved? (i.e., does ΔEsys =0?)
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2. Projectile #1: Tennis Ball Drop
Drop a tennis ball onto your partner’s hand from different heights. We are interested in the energy of
the ball from the instant you let it go un?l it lands in your partner’s hand.
Sketch the scenario iden?fying the system, the zero reference point, and ini?al and final points of
interest:
AHer impact on the hand, when the ball has landed on the hand, is the
kine?c energy zero (Yes/No)?
If yes, where did the ball’s energy go?
Is the gravita?onal poten?al energy greater, smaller or the same when it is
held at a higher loca?on?
LOL diagram:
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3. Sad Ball
Drop the sad ball onto the table top from the same height you used for the happy ball. We are
interested in the energy of the ball from the instant you let it go un?l impact with the table.
Energy Model (equa?on):
Will energy be conserved? (i.e., does ΔEsys =0?)
QUESTION 1: When dropped from a higher loca?on, is the kine?c energy (right before
hi^ng the hand) bigger or smaller than when dropped from the original height? Explain.
Sketch the scenario, identifying the system, the zero reference point, and initial and final points
of interest:
What is the kine?c energy at the moment of impact with the table?
What is the gravita?onal poten?al energy at the moment of impact with the table?
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Does the ball have some other energy at the moment of impact with the table? If yes, how do you
know and how is the ball storing the energy? [Hint: is the ball “squishy”?] If no, explain why not.
Does the ball transfer energy to the table? (Yes/No)
If your answer was YES: If your answer was NO:
How do you know energy was transferred to
the table?
How do you know energy was not transferred to
the table?
Did it transfer the energy by doing work?
Explain.
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LOL diagram:
Energy Model (eqn):
Will energy be conserved? (i.e., does ΔEsys =0?)
QUESTION 2: What’s the difference between the happy and sad balls, in terms of how
they store or release poten?al energy?
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4. Projectile #2: Horizontal Throw of Tennis Ball
Throw a tennis ball horizontally & let it hit the floor. We are interested in the energy from the moment
just before you start to throw it un?l the moment just before its impact on the floor. (You can ignore
the any bouncing or rolling.)
Sketch the scenario, iden?fying the system, the zero reference point, and ini?al and final points of
interest:
Before the throw, is the kine?c energy zero? (Yes/No)
AHer the throw, is the kine?c energy zero? (Yes/No)
During the horizontal throw, does the gravita?onal poten?al energy increase,
decrease or stay the same?
QUESTION 3: Did you do work on the ball? If yes, did you give or take energy from the
ball? If no, explain why you did not do work.
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5. Projectile #3: Catching a Ball
Throw a tennis ball to one of your partners. We are interested in the energy from the moment you
start to throw it to the moment the ball is at rest in your partner’s hand.
Pay aden?on to the movement of your hand as you throw and the movement of their hand when they
catch the ball; also note the height of your hand and the height of their hand.
LOL diagram:
Energy Model (eqn):
Will energy be conserved? (i.e., does ΔEsys =0?)
Sketch the scenario, identifying the system, the zero reference point, and initial and final points
of interest:
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Before the throw, is the kine?c energy zero? (Yes/No)
AHer the catch, is the kine?c energy zero? (Yes/No)
Did you do work on the ball? If yes, did you give or take energy from the ball? If no, explain why you
did not do work.
Did your partner do work on the ball? If yes, did your partner give or take energy from the ball? If no,
explain why your partner did not do work.
LOL diagram:
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6. Hanging Mass on a Spring
Hang a mass from a spring. We are interested in the moment where you pull the mass down (before
you release it) to the highest point that the mass moves to. We also care about when the mass is
moving its fastest.
In this case, the best place to put the zero reference is where the mass is hanging before you pull on it.
Energy Model (eqn):
Will energy be conserved? (i.e., does ΔEsys =0?)
Sketch the scenario, identifying the system, the zero reference point, and initial and final points
of interest:
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When the mass hangs from the spring but hasn’t been pulled on, does it
have poten?al energy? (Yes/No)
When you pull down on the mass, is its gravita?onal poten?al energy
posi?ve or nega?ve?
As the mass moves upwards towards its original posi?on, does the
gravita?onal poten?al energy get more posiOve, get more negaOve, or stay
the same?
As the mass moves upwards towards its original posi?on, does the spring
poten?al energy increase, decrease or stay the same?
As the mass moves upwards towards its original posi?on, does the kine?c
energy increase, decrease or stay the same?
LOL diagram (from ini?al stretch to highest point the mass moves to):
Energy Model (eqn):
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Will energy be conserved? (i.e., does ΔEsys =0?)
LOL diagram (from ini?al stretch to where the mass moves the fastest):
Energy Model (eqn):
Will energy be conserved? (i.e., does ΔEsys =0?)
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QUESTION 4: At what point in the mass’s mo?on is it moving the fastest? Explain.
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