Energy Changes

Energy Changes “Nothing endures but change” -Hercaclitus Energy is defined as the ability to cause a change. This simple definition was quite difficult for scientists to develop because energy comes in so many different forms. Energy is also intangible, meaning that it cannot be touched or calculated directly. You can see the many effects of energy such as a leaf blowing in the wind, the moving of a car or production of glucose by a plant cell. Energy is measured in joules (j). The amount of energy possessed by an object is dependent upon the object’s composition, position and velocity. Energy is conserved. You cannot create ti. You cannot destroy it. All you can do is change it from one form to another. We do not make electrical energy – we burn coal and turn its chemical energy into electrical energy. The motion of your car came from the chemical energy in the gasoline that powers it. All energy forms ultimately come from the sun, in the form of radiant energy. This radiant energy’s source was the nuclear energy that fuels the sun. Because energy is conserved, the amount of energy existing today in our universe is the same as the day when our universe began. When folks talk about the world “running out of energy”, what it really means is running out of one kind of energy. Most of the work of the modern world is done by converting chemical energy in coal and oil into kinetic energy (of vehicles), other forms of chemical energy (of fertilizers), heat energy (of buildings and dwellings), and radiant energy (light). We lack the technology to turn kinetic energy back into the chemical energy of coal and oil. Here is a partial list of the different kinds of energy: Kinetic Potential – elastic (a stretched spring) Gravitational (water piled up behind a dam) Heat (related to, but not the same as temperature) Chemical (gasoline) Radiant (light) Nuclear (typically from the breaking up of atoms – atomic power) Electrical (what is running my computer at I type this) Sound (screaming children give off a lot) All forms of energy can be categorized into one of two major forms: kinetic energy or potential energy. Kinetic energy is energy of motion. Sound energy involves the compression and rarefaction of air molecules (think of an opera singer shattering crystal glass), electrical energy involves the moving of electrons, nuclear energy involves the moving of atom parts, light energy involves the moving of photons, and heat energy involves the moving particles of matter. The amount of kinetic energy possessed by an object depends on its mass and velocity. Potential energy is stored energy. Objects with potential energy could cause a change if certain conditions are met. Chemical energy (think of a match and a

burning match), gravitational energy (think of water piled up behind a dam), and elastic energy (think of what happens when a stretched rubber band is released) are all types of potential energy. Use the definitions of kinetic energy and potential energy to decide what kind of energy each example listed below has. Write KE for kinetic energy and PE for potential energy. _____A moving skateboard _____A rock at the edge of a cliff _____A glass of milk _____Gasoline _____A basketball passing through the hoop _____A dry cell of a battery _____An acorn hanging from an oak tree _____A person climbing a ladder _____A piece of celery _____Blowing wind _____The springs of a sofa with someone sitting on it Now that you are finished, go back through the list. Of the examples that you labeled PE, decide if it is an example of gravitational, chemical, or elastic potential energy. Write a G for gravitational energy, a C for chemical energy and an E for elastic energy. The following set of experiments will allow you to explore several key concepts discussed in this handout.

Renewable Energy VS Non-Renewable Energy Materials needed: magnifying glass, 1 piece of black paper, wooden matches, aluminum pan, internet (optional) How is the electricity that is running your home produced?

How does this process demonstrate the conservation of energy?

What is renewable energy? Name a renewable energy? Light your match. Use caution so that you will not get burnt. Place the match on the aluminum pan and allow it to burn out. Before the match was lit, what type of energy did the match possess? Trace the energy conversions that were made after the match was lit.

Just like fossil fuels, we get heat and some pollution. What is the main form of pollution that was emitted from your match? Now light your match again. Just kidding. Of course, you can’t. Just like fossil fuels, once it its used it cannot be used again. If your home needs more heat, more fossil fuels must be burnt. Now let us look at renewable energy. Go outside; hold the magnifying glass perpendicular to the sun. Place the black paper underneath the magnifying glass. Move the paper toward the glass until the magnified sunlight is a small dot on the paper. The paper will begin to smoke and a hole should burn through.

Could you do the above experiment again? Of course! You could do the above experiment approximately 5 billion more years (that is the approximate time that the sun has left.) Compare and contrast the match experiment and the sun experiment.

Work Materials: household objects, meter stick/ ruler, scale, calculator, internet (optional) Define work. List 3 examples of work being done.

List 3 examples of work not being done.

Work can be calculated using the formula, W=F x d. Force as you may recall (or at least you should) is measured in Newtons (N) and distance is measured in meters (m). When these two quantities are multiplied…you end up with Nm (pronounced as Newton-meter). James Prescott Joule is the scientist that developed the work formula and ever so humbly equaled 1 Nm to 1 joule (J) after himself. So you may use either unit as you wish. 1. Use a scale and a meter stick to determine the amount of work you do in moving 3 different objects. Object

Force

Distance

Explain why another definition of energy is the “ability to do work”?

Work (include units)

Energy of a Pendulum Materials: Ruler, 2 pieces of string (20cm and 30cm), 2 different weights, watch with second hand. 1. Locate something to tie your mass to so that it can freely swing and tie one end of the short string. 2. Tie the other end to your smaller weight. 3. Hold the weight above the table to form an angle. 4. Release the pendulum and allow it to swing for 30 seconds. Count the number of full swings (back and forth) during the 30 seconds. Record this information in the chart below. 5. Run another trial and record. 6. Replace the small weight with the heavier one and repeat. 7. Repeat again using the longer string. PENDULUM String length Weight Size 15 cm Small 15 cm Large 25 cm Small 25 cm Large

NUMBER OF SWINGS IN 30 SECONDS Trial One Trial Two Average

1. Calculate the average number of swings for each trial. Record in the chart. 2. What type of energy does the pendulum have when it is hanging straight down? 3. What type of energy does the resting pendulum have if it is held at a right angle to the table? 4. What force acted on the pendulum when it was released from its raised position? 5. Which string length caused the pendulum to swing more times? 6. Which weight caused the pendulum the swing more times? 7. Describe the best method for increasing the number of swings of a pendulum during a set time period? 8. The diagram below represents a pendulum in motion. Look at the diagram and label it as indicated. a. Identify the maximum potential energy by writing the letter P on the diagram

b. Identify the position of maximum kinetic energy by writing the letter K on the diagram c. Identify the position where the kinetic energy increases by writing the letter I on the diagram d. Identify the position where the kinetic energy decreases by writing the letter D on the diagram

9. How does demonstrate the conservation of energy?

the pendulum experiment

Alka Seltzer Poppers Materials: old film canister, water, two Alka Seltzer tablets, paper towels, safety goggles Alka Seltzer tablets give off gas when they are placed in water. The chemical reaction that makes the bubbles is the same one that happens when you mix baking soda and vinegar. Vinegar is an acid, and that’s what makes it react wit baking soda. Alka Seltzer tablets have citric acid and baking soda already in them. All they need is water in order for the reaction to take place. **This activity will make a mess. You could do this outside to minimize clean-up** 1. Put your safety goggles on. 2. Fill the film canister about half full with water. 3. Drop about half a tablet in the water and quickly cap the container and stand back. 4. What did you observe? What happened to the cap of the film canister? 5. What kind of energy was contained within the tablet? 6. What kind of energy was it converted to ultimately?

7. Do you think that the reaction would proceed faster, slower, or at the same rate in water with a high temperature? What is the reasoning behind your answer? 8. How could you test this? Design an experiment to determine whether the reaction happens faster in hot or cold water.

9. What are the independent variable, dependent variable and constants of your experiment? 10.Perform your experiment. What did you find?

Making Electricity with Friction Materials: fluorescent bulb (tube), balloon Some books talk about the two kinds of electricity: static electricity and current electricity. But they are really the same thing! We can show this, and illustrate the conversion of energy into radiant energy. Turn off the light. Take the balloon and rub it in your hair or on your shirt to accumulate extra electrons on the balloon. Touch the balloon to the end of the light bulb. Did you see it flicker? Trace the energy changes that have occurred from rubbing the balloon to lighting the bulb. Why didn’t the bulb remain lit? Where did the energy go?

Splitting water

Materials: Film canister, 2 iron nails, Alka seltzer tablets, 9-volt battery or 6-volt, two plastic covered wires with alligator clips on the ends, matches, bubble solution, safety goggles. In this last experiment, we are going to convert electrical energy into chemical energy: we are going to make some fuel! The kind of fuel we are going to make is hydrogen gas. Water is made up of hydrogen and oxygen. If your break up water (which you can do by passing an electrical current through it) you can get hydrogen gas and oxygen gas. 1. Push a nail through the side of the film canister. Push the other nail through the opposite side. Yif you look into the canister, you should be able to see the tips of the nails. The nails should not be touching. 2. Fill the canister with sold water so that it covers the nails. 3. Add about a quarter of an alka seltzer tablet to the water and give it time to stop bubbling. 4. Now add electricity: Clip one alligator clip onto a nail and the other end to a battery terminal. 5. Take the second wire and clip one end to the other nail and the other clip to the other battery terminal. 6. Look inside your film canister. 7. You should see fizzing at both nail , but more fizzing at one nail. The nail with less fizzing is producing bubbles filled with oxygen gas. The nail that is fizzing faster is producing bubbles with hydrogen gas. Hydrogen gas burns; in fact you can use it to run a car! We are going to collect some of this fuel. What do you think would happen if you switched the wires at the battery terminals? Try it and find out. 1. Disconnect the battery. Take the lid of the film canister and use a nail to make a small hold in the center. Put the lid on the canister. 2. Now connect the battery again and let it run for a minute of two. 3. Touch the sides of the film canister; what do you notice? 4. Get a little bubble solution and put it over the hole in the top of the canister lid. 5. You should see bubbles. 6. Let a large bubble or several small ones form. Light a match and put it down close to the bubbles. Depending on the amount of hydrogen collected in the bubbles, you should hear / see a “pop” to a loud “explosion”. The longer you let bubbles collect, the bigger the explosion.

What kinds of energy did you start with and what kinds of energy do you end up with in this experiment. How might hydrogen gas be used to fuel a car? Do a little research on hydrogen cars and find out!