By considering the playground swing, looking in ~ diagrams, and also using real-world pendulums, student understand exactly how kinetic and also potential energy relate in ~ a system.

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LEARNING OBJECTIVES

Students understand how kinetic and potential power relate within a system. Students know the influence of friction ~ above the energy within a system.

Students construct and interpret graphical displays of data to define the relationships of kinetic energy to the mass of an item and come the speed of an object.

Students construct, use, and present debates to assistance the insurance claim that once the kinetic energy of an object changes, energy is transferred to or indigenous the object.

Teacher Tips

If you take place to teach near a waver set, part 1 that this activity is a an excellent opportunity to take it a mini ar trip, either to watch younger kids swinging or to suffer the swing of a pendulum kinesthetically.

Materials

tiny metal washer (or similar) string

Teacher Tune-ups


This illustration is intended to expand the ide that an item can have both kinetic and potential energy. Three kids are swinging and also each is in a different position. Students space asked to take into consideration which child has the many potential energy and which has the many kinetic energy.

You may ask students to think for a moment, write down a response, and then to comment on within a team or v a partner. In any type of case, enable sufficient time because that students to justify their responses.

It isn’t necessary that students recognize all principles at this point.

Continue come elicit responses until many of this points are mentioned:

son #1 shows up to be just sitting on the swing. So this boy has little or no kinetic or potential energy. Son #3 is at the top of the arc the his swing. If that is specifically at the top of the swing, the is not relocating up or relocating down (zero kinetic energy). The is motionless for just a split second before relocating down. In this situation he has no kinetic energy yet plenty that potential energy. In one more split 2nd he will certainly plummet down and also have kinetic energy. The is improbable the a child is totally stationary, so even if in ~ the precise top the the swing, he has actually both kinetic and potential energies. Boy #2 is moving backwards. She now has the biggest amount that kinetic energy of the three children. Her velocity is biggest of the three. She also appears to it is in the largest child, so her mass is the highest. Her momentum is likewise the greatest. Child #1 has the the very least potential energy, zero. Child #3 has much more potential power than boy #2 (even though child #2 appears to have an ext mass), because the facility of fixed of boy #3 is about four times further over the bottom that the arcs than that of boy #2.
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Sometimes objects have actually both kinetic and potential energy. Let’s say that child #1 is simply sitting on the swing and not relocating at all. Kid #2 is moving backward. Her place moments earlier was as with Child #3. Speaking of boy #3, that is at the very highest suggest of his swing.

TURN and also TALK:

Of the three children swinging, i beg your pardon is displaying the many kinetic energy? The most potential energy?

Explain your thinking:

Is over there another suggest at which son #2 or #3 will have much more kinetic energy? more potential energy?


Making a Pendulum: have actually students do a pendulum come investigate how potential power becomes kinetic energy and how kinetic power becomes potential energy.

Any thin cotton string or strong thread will perform for this demonstration. A thick string won’t swing well. Washers are basic to tie and heavy, but other objects will work. The washer should be at least ½ inch in diameter. (Smaller people aren’t heavy enough.)

Paraphrase:

One student holds the finish of the string if the second holds the washer so the the wire is taut and then publication the washer. The human holding the wire shouldn’t relocate his or her hand – no same swinging the washer!

Ask students come think about what type of power the pendulum has actually when the washer is in various positions: as soon as it is at the peak of the swing, halfway come the bottom, in ~ the bottom, and halfway come the top.

Students should talk about the concerns with your partners and then write their conclusions. Take into consideration having students existing their responses come the totality class.

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Additional questions for college student to discover with a pendulum:

walk the length of the string impact the period? The mass of the washer? allude of release?
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This illustration and also graph describe how and when energy transfers on a an easy pendulum.

Paraphrase:

As the washer swings down, potential power is transformed right into kinetic energy. At the bottom that the waver all power is kinetic energy. Together the washer move up, kinetic energy is transformed right into potential energy. In ~ its highest point in the arc of the swing, as soon as again the power is every potential energy.

Discuss these points through the class:

When your partner moved the washer to the left or appropriate from its resting position, that or she provided the pendulum potential energy. It to be potential energy due to the fact that the washer might swing as result of its loved one position and gravity. This sort of potential power is well-known as gravitational potential energy.

What’s interesting around a pendulum, though, is that when you let walk of it, the potential energy gradually transforms right into kinetic energy. And then it gets faster and also faster until it reaches the lowest suggest of the swing. In ~ that allude the kinetic power starts transforming earlier into potential power on the other finish of the swing. Then, the pendulum actually involves a stop! It involves a avoid for a really short time at the finish of each swing. Once it is “at rest” the energy is when again potential energy.

With this an excellent system going, you might think the pendulum would never stop. Yet as you observed, it does certainly stop swinging after a while. Yet why? whereby did all that power go?


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Paraphrase:

The transfer repeats together the washer ferris wheel to the right and left. Friction eventually slows and also stops the motion. Friction is the force that holds back a moving object. Friction is current where her fingers fulfill the string and also where the string touches the washer.

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In a system with no friction, the pendulum would proceed to totter forever.

Ask:

Why go the swinging slow-moving over time?

Answer:

(Many will offer gravity together the cause, however that is not the case.)

The washer (and the string) is actually banging right into something together it swings. Yet what? wait MOLECULES, of course! Swing her hand earlier and forth and also feel them because that yourself! yet an even more far-reaching reason because that the pendulum slowing down is the friction in between the string and also your fingers and the friction of the different parts the the wire itself.