Potential Energy Exercises

Saturday November 7, 2009

Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.
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1. What is potential energy?


2. What is gravitational potential energy?


3. Where is the potential energy greatest?


4. Where is potential energy lowest?


5. Give an example of where potential energy decreases.


6. What is work?


7. What does a Newton measure?


8. What does a Joule measure?


Need answers?


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Answers to Potential Energy Exercises

Saturday November 7, 2009

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!


Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for K-8 and here for K-12.


Answers:
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1. Potential energy is the energy that something has that can be released.


2. Gravitational potential energy is the energy something has due to gravity. Gravitational Potential Energy = mgh


3. Potential energy is greatest when a heavy object is up high, like a bowling ball falling from an airplane.


4. Potential energy is lowest at the surface of the Earth. The object is as low as it can get.


5. Potential energy decreases as an object falls to the Earth.


6. Work is defined as moving an object over a distance against a force. Work = force x distance


7. A Newton is a unit of force. How much force it takes to push or pull something. It takes about one Newton of force to lift an apple.


8. A Joule is a unit of energy. It takes one Joule to exert one Newton of force over a distance of one meter.


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Mystery Toy

Saturday November 7, 2009

Note: Do the pendulum experiment first, and when you’re done with the heavy nut from that activity, just use it in this experiment.


You can easily create one of these mystery toys out of an old baking powder can, a heavy rock, two paper clips, and a rubber band (at least 3″ x 1/4″).  It will keep small kids and cats busy for hours.


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Here’s what you get:


  • can with a lid
  • heavy rock or large nut
  • two paper clips
  • rubber band

You’ll need two holds punched through your container  – one in the lid and the bottom. Thread your rubber band through the heavy washer and tie it off (this is important!).  Poke the ends of the rubber band through one of the holes and catch it on the other side with a paper clip.  (Just push a paper clip partway through so the rubber band doesn’t slip back through the hole.)  Do this for both sides, and make sure that your rubber band is a pulled mildly-tight inside the can.  You want the hexnut to dangle in the center of the can without touching the sides of the container.



 
Download Student Worksheet & Exercises


Now for the fun part… gently roll the can on a smooth floor away from you.  The can should roll, slow down, stop, and return to  you!  If it doesn’t, check the rubber band tightness inside the can.


The hexnut is a weight that twists up the rubber band as the can rolls around it.  The kinetic energy (the rolling motion of the can) transforms into potential (elastic) energy stored in the rubber band the free side twists around. The can stops (this is the point of highest potential energy) and returns to you (potential energy is being transformed into kinetic). The farther the toy is rolled the more elastic potential energy it stores.


Exercises


  1. Explain in your own words two types of energy transfer:
  2. True or false: All energy in a system is lost to heat.
    1. True
    2. False

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Unit 5: Energy (Potential) Video

Saturday November 7, 2009

This lesson we’re going to talk about the two main categories of energy: potential and kinetic. We will talk about transfer of energy and we will also discuss conservation of energy and energy efficiency. This video gets you started on the right foot. We’ll outline what’s coming up for this week and how to get the most out of our lesson together. Enjoy!



Whackapow!

Saturday November 7, 2009

In this experiment, you’re looking for two different things:  first you’ll be dropping objects and making craters in a bowl of flour to see how energy is transformed from potential to kinetic, but you’ll also note that no matter how carefully you do the experiment, you’ll never get the same exact impact location twice.


To get started, you’ll need to gather your materials for this experiment. Here’s what you need:


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  • several balls of different weights no bigger then the size of a baseball (golf ball, racket ball, ping pong ball, marble etc. are good choices)
  • fill a good size container or mixing bowl with flour or corn starch (or any kind of light powder)
  • If you’re measuring your results, you’ll also need a tape measure (or yard stick) and a spring scale (or kitchen scale).

Are you ready?


1. Fill the container about 2 inches or so deep with the flour.


2. Weigh one of the balls (If you can, weigh it in grams).


3. Hold the ball about 3 feet (one meter) above the container with the flour.


4. Drop the ball.


5. Whackapow! Now take a look at how deep the ball went and how far the flour spread. (If all your balls are the same size but different weights it’s worth it to measure the size of the splash and the depth the ball went. If they are not, don’t worry about it. The different sizes will effect the splash and depth erratically.


6. Try it with different balls. Be sure to record the mass of each ball and calculate the potential energy for each ball.



Each one of the balls you dropped had a certain amount of potential energy that depended on the mass of the ball and the height it was dropped from. As the ball dropped the potential energy changed to kinetic energy until, “whackapow”, the kinetic energy of the ball collided with and scattered the flour. The kinetic energy of the ball transferred kinetic energy and heat energy to the flour.


For Advanced Students:

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Calculate the gravitational potential energy of the ball. Take the mass of the ball, multiply it by 10 m/s2 and multiply that by 1 meter. For example, if your ball had a mass of 70 grams (you need to convert that to kilograms so divide it by 1000 so that would be .07 grams) your calculation would be


PE=.07 x 10 x 1 = .7 Joules of potential energy.


So, how much kinetic energy did the ball in the example have the moment it impacted the flour? Well, if all the potential energy of the ball transfers to kinetic energy, the ball has .7 Joules of kinetic energy.


Create a table in your science journal or use ours. (You’ll need Microsoft Excel to use this file.)


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Ball Bounce

Saturday November 7, 2009

When you toss down a ball, gravity pulls on the ball as it falls (creating kinetic energy) until it smacks the pavement, converting it back to potential energy as it bounces up again. This cycles between kinetic and potential energy as long as the ball continues to bounce.


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But note that when you drop the ball, it doesn’t rise up to the same height again. If the ball did return to the same height, this means you recovered all the kinetic energy into potential energy and you have a 100% efficient machine at work. But that’s not what happens, is it? Where did the rest of the energy go? Some of the energy was lost as heat and sound. (Did you hear something when the ball hit the floor?)



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Elastic Potential Energy

Saturday November 7, 2009

There are many different kinds of potential energy.  We’ve already worked with gravitational potential energy, so let’s take a look at elastic potential energy.


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Materials: a rubber band


A simple way to demonstrate elastic energy is to stretch a rubber band without releasing it.  The stretch in the rubber band is your potential energy. When you let go of the rubber band, you are releasing the potential energy, and when you aim it toward a wall, it’s converted into motion (kinetic energy).



Here’s another fun example:  the rubber band can also show how every is converted from one form to another.  If you place the rubber band against a part of you that is sensitive to temperature changes (like a cheek or upper lip), you can sense when the band heats up.  Simply stretch and release the rubber band over and over, testing the temperature as you go. Does it feel warmer in certain spots, or in just one location?


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Pendulums

Saturday November 7, 2009

This is a very simple yet powerful demonstration that shows how potential energy and kinetic energy transfer from one to the other and back again, over and over.  Once you wrap your head around this concept, you'll be well on your way to designing world-class roller coasters.

For these experiments, find your materials:

  • some string
  • a bit of tape
  • a washer or a weight of some kind
  • set of magnets (at least 6, but more is better)

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Here's what you do:

1. Make the string into a 2 foot or so length.

2. Tie the string to the washer, or weight.

3. Tape the other end of the string to a table.

4. Lift the weight and let go, causing the weight to swing back and forth at the end of the pendulum.

Download Student Worksheet & Exercises

Watch the pendulum for a bit and describe what it’s doing as far as energy goes. Some questions to think about include:

  • Where is the potential energy greatest?
  • Where is the kinetic energy greatest?
  • Where is potential energy lowest?
  • Where is kinetic energy lowest?
  • Where is KE increasing, and PE is decreasing?
  • Where is PE increasing and KE decreasing?
  • Where did the energy come from in the first place?

Remember, potential energy is highest where the weight is the highest.

Kinetic energy is highest were the weight is moving the fastest. So potential energy is highest at the ends of the swings. Here’s a coincidence, that’s also where kinetic energy is the lowest since the weight is moving the least.

Where’s potential energy the lowest? At the middle or lowest part of the swing. Another coincidence, this is where kinetic energy is the highest! Now, wait a minute...coincidence or physics? It’s physics right?

In fact, it’s conservation of energy. No energy is created or destroyed, so as PE gets lower KE must get higher. As KE gets higher PE must get lower. It’s the law...the law of conservation of energy! Lastly, where did the energy come from in the first place? It came from you. You added energy (increased PE) when you lifted the weight.

(By the way, you did work on the weight by lifting it the distance you lifted it. You put a certain amount of Joules of energy into the pendulum system. Where did you get that energy? From your morning Wheaties!)

Chaos Pendulum

For this next experiment, we'll be using magnets to add energy into the system by having a magnetic pendulum interact with magnets carefully spaced around the pendulum. Watch the video to learn how to set this one up.  You'll need a set of magnets (at least one of them is a ring magnet so you can easily thread a string through it), tape, string, and a table or chair. Are you ready?

Exercises

  1. Why can we never make a machine that powers itself over and over again?
    1. Energy is mostly lost to heat.
    2. Energy is completely used up.
    3. Energy is unlimited, but is absorbed by neighboring air molecules.
    4. None of these
  2. In the pendulum, as kinetic energy increases, potential energy ______________.
    1. Increases
    2. Decreases
  3. As potential energy decreases, kinetic energy _________________.
    1. Increases
    2. Decreases

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