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Physics 2015: Mechanical Energy Conservation Purpose Study energy conservation by looking at the relationship between three different types of energy:

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Presentation on theme: "Physics 2015: Mechanical Energy Conservation Purpose Study energy conservation by looking at the relationship between three different types of energy:"— Presentation transcript:

1 Physics 2015: Mechanical Energy Conservation Purpose Study energy conservation by looking at the relationship between three different types of energy:  Gravitational potential energy (GPE)  Elastic potential energy (EPE)  Kinetic energy (KE)

2 Physics 2015: Mechanical Energy Conservation Energy is “conserved” if we can add up all of the different types of energy present in a closed system and see that the total sum remains constant.  A “closed system” is one where no energy is added to or taken away from the system (in our case, a system with negligible friction)  The types of energy will change depending on the setup. Ours were listed on the previous slide.

3 Physics 2015: Mechanical Energy Conservation Different Energy Types Gravitational Potential Energy (GPE) (relative to a vertical level where h=0) Elastic Potential Energy (EPE) (k=spring constant x=distance stretched) Kinetic Energy (KE) (m=mass v= velocity) Heat Energy (Friction can turn KE into heat energy, for example) Your choice where that is – be smart about it!

4 Physics 2015: Mechanical Energy Conservation Our Setup in the Lab photogate Note as the system is released, the quantity GPE+EPE+KE should stay the same. We will be able to measure all three energies (and thus their sum) at two different points of the cart’s travel and compare.

5 Physics 2015: Mechanical Energy Conservation Activity I - Find the spring constant k Hook’s law: F = - k x  Attach different masses.  Measure the change of length of the spring compared to it’s un-stretched length.  You can plot your data in Excel and use linear regression to find the slope k. mmgx x slope = k measured calculated

6 Physics 2015: Mechanical Energy Conservation Activity II - Conserving Energy. photogate  Decide where you want to make your GPE=0. A good choice will make your calculations a lot easier.  Measure all masses (including the mass of the cart).  Set photogate such that the cart will pass through it (to measure it’s velocity) as the hanging mass accelerates the cart to the left.

7 Physics 2015: Mechanical Energy Conservation Hints If you do find an energy change, ask whether your “system” was totally “closed”. Was some form of energy not accounted for?

8 Physics 2015: Mechanical Energy Conservation Correction There is a mistake in the lab manual on page 75: In the paragraph at the top of the page it says: “…create a scatter plot with Excel that graphs position on the vertical axis and Force on the horizontal axis….” It should be the other way around: You need to plot Force on the vertical axis and position on the horizontal axis. Please correct that in your manual now before you forget….


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