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110-Lab06-EnergyII.docx

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PHYS 110 Lab #8: Energy II

The big idea:

Applying energy models

In this lab you will be practicing creating and applying energy models for several different scenarios.

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 until the highest point it reaches after one bounce. We’ll also investigate the moment of impact with the table.

Sketch the scenario identifying the system, the zero reference point, and initial and final points of interest:

As the ball falls, does the gravitational potential energy increase, decrease or stay the same?

As the ball falls, does the kinetic energy increase, decrease or stay the same?

On the way up (after the bounce), does the potential energy increase, decrease or stay the same?

On the way up (after the bounce), does the kinetic energy increase, decrease or stay the same?

What is the kinetic energy at the moment of impact with the table?

What is the gravitational potential energy at the moment of impact with the table?

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 (initial drop and impact with table):

Energy Model (equation) (for the initial drop and impact with the table):

Will energy be conserved? (i.e., does ΔEsys =0?)

Now you’ll repeat the analysis with the initial drop and the final height that the ball reaches.

LOL diagram (initial drop and final height):

Energy Model (equation) (for initial drop and final height):

Will energy be conserved? (i.e., does ΔEsys =0?)

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 until it lands in your partner’s hand.

Sketch the scenario identifying the system, the zero reference point, and initial and final points of interest:

After impact on the hand, when the ball has landed on the hand, is the kinetic energy zero (Yes/No)?

If yes, where did the ball’s energy go?

Is the gravitational potential energy greater, smaller or the same when it is held at a higher location?

LOL diagram:

Energy Model (equation):

Will energy be conserved? (i.e., does ΔEsys =0?)

Picture 4

QUESTION 1: When dropped from a higher location, is the kinetic energy (right before hitting the hand) bigger or smaller than when dropped from the original height? Explain.

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 until impact with the table.

Sketch the scenario, identifying the system, the zero reference point, and initial and final points of interest:

What is the kinetic energy at the moment of impact with the table?

What is the gravitational potential energy at the moment of impact with the table?

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.

LOL diagram:

Energy Model (eqn):

Will energy be conserved? (i.e., does ΔEsys =0?)

Picture 4

QUESTION 2: What’s the difference between the happy and sad balls, in terms of how they store or release potential energy?

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 until the moment just before its impact on the floor. (You can ignore the any bouncing or rolling.)

Sketch the scenario, identifying the system, the zero reference point, and initial and final points of interest:

Before the throw, is the kinetic energy zero? (Yes/No)

After the throw, is the kinetic energy zero? (Yes/No)

During the horizontal throw, does the gravitational potential energy increase, decrease or stay the same?

Picture 4

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.

LOL diagram:

Energy Model (eqn):

Will energy be conserved? (i.e., does ΔEsys =0?)

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 attention 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.

Sketch the scenario, identifying the system, the zero reference point, and initial and final points of interest:

Before the throw, is the kinetic energy zero? (Yes/No)

After the catch, is the kinetic 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:

Energy Model (eqn):

Will energy be conserved? (i.e., does ΔEsys =0?)

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.

Sketch the scenario, identifying the system, the zero reference point, and initial and final points of interest:

When the mass hangs from the spring but hasn’t been pulled on, does it have potential energy? (Yes/No)

When you pull down on the mass, is its gravitational potential energy positive or negative?

As the mass moves upwards towards its original position, does the gravitational potential energy get more positive, get more negative, or stay the same?

As the mass moves upwards towards its original position, does the spring potential energy increase, decrease or stay the same?

As the mass moves upwards towards its original position, does the kinetic energy increase, decrease or stay the same?

LOL diagram (from initial stretch to highest point the mass moves to):

Energy Model (eqn):

Will energy be conserved? (i.e., does ΔEsys =0?)

LOL diagram (from initial stretch to where the mass moves the fastest):

Energy Model (eqn):

Will energy be conserved? (i.e., does ΔEsys =0?)

Picture 4

QUESTION 4: At what point in the mass’s motion is it moving the fastest? Explain.

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