Investigating How Forces Transfer Energy Investigation #1 Getting To Work With Energy Investigating How Forces Transfer Energy

ENERGY What is ENERGY? What do you think of when you hear the word ENERGY? Why is energy so important to us? What types of energy do you encounter most often? How does energy get from one place to another?

ENERGY defined … Energy is a term that is used often, yet is very difficult to define. Energy is typically defined by the CHANGE that is caused when energy changes form or moves form one object to another object. The concept of energy flow is one of the most fundamental ideas in all of science.

Dropping Golf Balls ... You will drop the golf ball from four different heights looking for evidence of energy by a change that is produced.

Investigation Reflection: Question #1: Does the golf ball have energy while it is sitting on the top of the sand? (Assume that the sand represents the ground) Pick up the golf ball and hold it about 25 cm above the pan. Question #2: What type of energy does the golf ball have while the ball is being held at a height of 25cm above the pan? Question #3: How did the golf ball get its energy? Where did this energy come from? Release the ball and discuss the crater produced by the golf ball.

Repeat the process from 50 cm, 75 cm, and 100 cm (1m) Repeat the process from 50 cm, 75 cm, and 100 cm (1m). Discuss why the craters are larger as the height increases; what we see is a greater CHANGE. Drop each trial’s ball in a different spot in the sand so that they can be compared in the end. Question #4: Which trial created the most change in the sand (the largest crater)? Introduce a hollow practice golf ball into the investigation. Repeat the same process as was done with the solid golf ball. Question #5: What variable was changed in this part of the investigation? What effect did this change have on the crater in the sand? Question #6: Did the hollow ball and the solid ball impact the sand with the same speed? In other words, did gravity speed them up both golf balls at the same rate? Question #7: What can you conclude from our investigation?

Review of Energy Forms

Mechanical Energy Kinetic Energy (KE) - the energy of motion. The energy associated with moving objects is called kinetic energy (KE), and is often referred to as the most fundamental form of energy. The size of the KE is determined by an object’s speed and its mass. A moving baseball has kinetic energy. If you have ever been hit by a pitched ball, you are aware of the energy a moving object can have. Give three examples of other objects that may have kinetic energy. Gravitational Potential Energy (GPE) - the energy of position. This is energy that an object possesses due to its position. The size of the GPE is determined by the object’s mass and its height above the ground. A person climbing a ladder increases her height above the ground, she increases her GPE. Give three examples of objects with gravitational potential energy.

Heat Energy (HE) - the random kinetic energy of particles Heat Energy (HE) - the random kinetic energy of particles. Heat energy is the random, and very disorganized, kinetic energy of the particles in a substance. Thermal energy is another term often used as a synonym for heat energy. In most cases the distinction between the exact definitions of heat energy and thermal energy is not made. Due to the random nature of this form of energy, it is difficult to make heat energy a useful form of energy. For this reason it is usually the form of energy that appears at the end of energy chains. It happens so often that scientists refer to heat energy as the “graveyard of energy”. For example, if you pound a nail into a piece of wood, the nail gets hot due to the energy transferred to it by the hammer and the force of friction with the wood. Give three examples of objects that have thermal energy.

Chemical Potential Energy (CPE) - the energy of bonds Chemical Potential Energy (CPE) - the energy of bonds. Chemical potential energy, sometimes just called chemical energy, is the energy stored in the bonds that hold the particles in a substance together. When these bonds are formed, or are broken, energy transfers and/or transformations take place. In many cases, the energy stored in the bonds of substances is transformed into other forms of energy. Food is a source of chemical energy for our bodies, so we sometimes use ‘food energy’ in place of chemical energy in energy chains that involve people. In most cases this chemical potential energy is later transformed into heat energy Give three other examples of chemical potential energy.

Electromagnetic Energy - the energy of waves Electromagnetic Energy - the energy of waves. This form of energy is often referred to as solar energy and light energy as well. Electromagnetic energy is the energy that is carried by electromagnetic waves. The most common form of electromagnetic energy is “light”. Light energy is a term that can be used to describe the energy ranges that our human eyes are sensitive to and it may include some forms of ‘light’ that we can not see with our eyes, such as infrared and ultraviolet. The sun is the most important source of electromagnetic energy, supplying the vast majority of our planet’s energy. In some cases, chemical potential energy can be transformed into electromagnetic energy. This form of energy is very important in the scientific field of astronomy. Electrical energy is a subset of electromagnetic energy, characterized by moving charges. It is used to run appliances and make artificial light. When the charged particles vibrate, they transfer energy by electromagnetic waves. Give three other examples of electromagnetic energy.

Sound Energy - the energy of vibrating particles Sound Energy - the energy of vibrating particles. This form of energy is transferred by mechanical waves. The particles that make up a substance vibrate in a highly organized manner and transfer energy through the substance. The particles in the substance vibrate, but do not change their location. In most cases, sound energy is classified into three categories; infrasonic is the sound that is below our human hearing level, sonic is the sound that our human ears are sensitive to, and ultrasonic is the sound that is above our human hearing level. Have you ever made a tin can telephone? If so, you have already experimented with sound waves and how vibrations are involved in the energy transfer process. A good example of the use of sound waves is sonar. Humans have created devices that enable us to send out a sound wave and listen for the echo so that we can determine how far away something is to the source. Seismic waves or “earthquake” waves also fit into this category because they involve the transfer of energy through vibrating matter in the form of mechanical waves. Ultrasounds in the medical field are used for a variety of purposes. Perhaps you have seen an ultrasound image of a baby. In most energy chains, the sound energy is transformed into heat energy (the disorganized and random KE of particles). Give three other examples of sound energy.

Elastic Potential Energy (EPE) - energy of deformed materials Elastic Potential Energy (EPE) - energy of deformed materials. This form of energy comes from the stretching or compressing of elastic materials. When an elastic material is deformed (by stretching or compressing), it exerts a force, called the elastic force, to return to its original shape. In many cases, the elastic material is held temporarily in this deformed position and the material has a stored amount of energy. Bow hunters make use of EPE to shoot their arrows. The EPE of the bow string is converted to the KE of the arrow. Catapults and slingshots also operate in this manner. Tennis players rely on the elastic properties of their tennis racquets and the tennis ball. Pole vaulters depend on the stored energy in the bent pole to help them get over the bar. The science behind the design of the pole relies on knowledge of how material store EPE. Surprisingly, certain types of rock can have elastic properties. They can be stretched or compressed under huge forces. Give three other examples of elastic potential energy.

Energy Transfer vs. Energy Transformation Energy TRANSFER is the passing of energy from one object to another object. Energy TRANSFORMATION is the changing of energy from one form of energy to another form of energy.

Energy can not be created nor destroyed Energy can not be created nor destroyed. Energy can be transferred from one object to another and can be transformed from one form to another, but the total amount of energy never changes.

Energy Chains Energy chains are graphical representations of the flow of energy in a system. They typically contain words, phrases, and images.

Forces That Transfer Energy Making Crash Barriers

Investigating How Forces Transfer Energy Part A: Creating a Barrier Focus Question: What barrier design will stop the car in the shortest distance? Your task is to create a stopping barrier out of dominoes that will stop the car in the shortest distance possible.

Pre-Investigation Questions Question #1: What form of energy is present when the car is sitting at the top of the ramp? How do you know this? Question #2: What will happen to the energy of the car as it moves down the ramp? What evidence could you collect to justify your answer? Question #3: When the car strikes the barrier what will happen to the energy of the car? How do you know this? Question #4: Let’s assume we release the car from rest at the top of your ramp. What can you do to be sure that the car strikes your barrier with the same KE in each trial? Explain.

Conduct your Investigation Record your results carefully and be prepared to report to the class the design of your barrier that stopped the car in the shortest distance by exerting the largest stopping force and the answers to the questions asked below. Question #5: What forces are causing the car to stop? Question #6: Why is the stopping distance shorter for some arrangements of blocks than for other arrangements?

Stopping Distances:

Investigating How Forces Transfer Energy Part B: Creating a Safe Stopping Barrier Focus Question: What is the shortest distance that your car needs to safely stop the moving car? Your task is to create a stopping barrier out of dominoes that will stop the car safely (the domino passenger can not fall over or out of the car) in the shortest distance possible.

Stopping Distances:

Investigation Reflection: Question #7: How did the smallest “safe” stopping distance from Part B compare to the stopping distance in Part A? Question #8: Can you think of other materials that would make safer barriers than the ones you made out of blocks? Explain why you think these other materials would make safer barriers?

WORK The Transfer of Energy How does the previous investigation help us to understand how forces transfer energy?

(Fs) x (D ) = (Fs) x (D ) = ( KE )

SAFER Crash Barriers An excellent application of these concepts is the “soft walls” used by major racing facilities across the nation (Dover International Speedway being one of these). The new SAFER (Steel And Foam Energy Reduction) barriers have revolutionized the sport of automobile racing and made it much safer for both the drivers and the fans.

So how do SAFER barriers absorb energy? The barriers move upon impact so that the KE of the car is transferred to a very large area of the wall (a large portion of the wall flexes upon impact). The key idea is that no one portion of the wall receives a large amount of the car’s KE. The KE of the flexing soft wall is then transferred to the outer permanent wall and support structure. The materials that make up the wall are not elastic. Imagine what the collision would be like if the wall was elastic! Still other portions of the car’s initial KE are transformed into heat energy and sound energy.