Science Praxis: Energy

In everyday life, people think of heat and thermal energy as the same thing, however in science, ..... is the energy transferred from a hot object to a cooler object.

heat

The process of ......, or the movement of thermal energy from one material to another, can be exothermic or endothermic for a given substance.

heat transfer

Substances at higher temperatures transfer heat to substances at lower temperatures. This transfer only occurs in one direction: from .......... . The hotter substance always loses thermal energy and the colder substance always gains thermal energy.

hot to cold

More massive and faster objects have more ........ energy than less massive and slower objects. For example, the ....... energy of a semi-truck moving is greater than that of a sports car moving the same speed, but the kinetic energy of a flying bullet is greater than a man resting in a hammock.

kinetic

Conservation of energy is one of the most fundamental principles of science. Energy is "....." as heat, but it wasn't destroyed.

lost

Fossil fuel use is very prevalent because fossil fuels are cheap, easy to access, and have a high energy density. However, they are ......, meaning they will eventually run out.

non-renewable resources

may be classified as kinetic ... potential energy. This includes solar, wind, magnetic, nuclear, sound, heat, light, electrical, and electromagnetic.

or

The discussion of an exothermic or an endothermic process refers to what happens to the thermal energy of a given substance. In ...., the substance loses. In ..., the substance gains.

exo endo

People have been using fossil fuels in the United States as a source of energy for many, many years. Why are scientists now searching for alternative fuel sources? Select all answers that apply. A Fossil fuels are a non-renewable resource. B Alternative fuel sources create less pollution than burning fossil fuels. C Alternative fuel plants are less expensive to build than coal plants. D Fossil fuels are only found in the United States.

A, B

A wind turbine converts: A kinetic energy into electrical energy. B radiation into electrical energy. C chemical energy into potential energy. D potential energy into kinetic energy.

A, Wind supplies kinetic energy, which is converted to mechanical energy within a wind turbineand then to electrical energy by the wind turbine's generator.

The table lists the three ways thermal energy can be transferred. Which phrase would best replace the letter Z, which represents an example of radiation? A you can feel the heat coming from the light bulb in a lamp B the handle of an iron skillet gets hot while the skillet sits on a hot stove C the air is warmer on the top bunk bed than it is on the bottom one D the end of a metal spoon gets hot while sitting in a bowl of hot soup

A.

When a panel absorbs energy from the sun to power a yard light, which of the following best describes the transfer of energy? A solar energy to light energy B nuclear energy to light energy C geothermal energy to light energy D hydroelectric energy to light energy

A.

Compared with the thermal energy and temperature of a baked potato just out of the oven, an olympic-sized swimming pool has: A a greater thermal energy but a lower temperature. B a greater thermal energy and a higher temperature. C a lower thermal energy but a higher temperature. D a lower thermal energy and a lower temperature.

A. A swimming pool has many moving molecules that contribute to its thermal energy, but the average kinetic energy (temperature) of the molecules in the pool is less than the average kinetic energy of the molecules in the potato right out of an oven.

Jennifer moves her wheelchair up a ramp to enter a building. The ramp she is using is an example of which simple machine? A an inclined plane B a pulley C a wheel D a lever

A. All the answers listed are simple machines. An inclined plane, or ramp, is the example of a simple machine which increases the distance of travel but decreases the force needed.

A girl is sledding down a hill. At which point would she have the least potential energy? A at the top of the hill B as she is sledding down the hill C as she is walking up the hill, carrying the sled D at the bottom of the

A. An object's potential energy increases with height. The girl would have the most potential energy at the top of the hill and the least at the bottom of the hill.

Which of the following best summarizes the energy transformations that occur in a car engine while the engine is running? A chemical energy to mechanical energy B electrical energy to chemical energy C chemical energy to potential energy D thermal energy to chemical energy

A. Chemical energy stored in the fuel is converted to thermal energy when the fuel is burned. The thermal energy, in turn, is converted to mechanical energy.

Which of the following is the principal type of energy stored behind a hydroelectric dam? A gravitational potential energy B chemical potential energy C heat D mechanical

A. Gravitational potential energy is energy stored due to the position of an object. The water held behind the dam has gravitational potential energy and can be converted as it flows through the dam to the river below.

A system has 45 J of kinetic energy and 15 J of potential energy. What is the mechanical energy of the system? A 60 J B 15 J C 45 J D 30 J

A. Mechanical energy equals kinetic energy plus potential energy. In this case, 45 J + 15 J = 60 J.

Mr. Montana and Mr. Perry both purchase the same model of refrigerator. Mr. Montana pushes his refrigerator up a frictionless ramp and into his truck. Mr. Perry picks his refrigerator up and directly lifts it into his truck. Who does more work? A They do the same amount of work. B Mr. Perry does more work. C Mr. Montana does more work. D It is impossible to tell with the information given.

A. Simple machines do not change the amount of work that is done. Since work = force x distance, they can only change the force and the distance over which the force is applied. The amount of force needed to lift the refrigerator is greater than the amount of force needed to push the refrigerator up the ramp. When the refrigerator is pushed up a ramp, the ramp holds some of the refrigerator's weight, requiring less force to move the refrigerator up the ramp. However, Mr. Montana must push over a greater distance.

Mr. Montana and Mr. Perry both purchase the same model of refrigerator. Mr. Montana pushes his refrigerator up a frictionless ramp and into his truck. Mr. Perry picks his refrigerator up and directly lifts it into his truck. Who applied more force in moving the refrigerator and why? A Mr. Perry because he had to lift the entire weight. Mr. Montana did not need to apply as much force, but had to push the refrigerator a greater distance (up the ramp). Both did the same amount of work. B Mr. Montana because the amount of force to push the refrigerator up the ramp must exceed the force of gravity pulling the refrigerator down the ramp. C Mr. Perry because more work is needed to lift the refrigerator straight up than to walk up a ramp. D They applied equal forces because both refrigerators have the same weight.

A. The amount of force needed to lift the refrigerator is greater than the amount of force needed to push the refrigerator up the ramp. When the refrigerator is pushed up a ramp, the ramp holds some of the refrigerator's weight, requiring less force to move the refrigerator up the ramp. However, Mr. Montana must push over a greater distance.

Which of the following is an example of thermal energy? A The motion or vibration of particles of matter. B Frictional forces that occur when a person quickly rubs her hands together. C Solar radiation. D The change in temperature of a person sitting in a hot bath.

A. Thermal energy is stored in the vibrations of atoms and molecules in matter.

Why does a simple machine (pulley, inclined plane, lever) make work easier? Select all answers that apply. A It can increase the distance an object travels. B It can decrease the amount of work needed to move an object. C It can change the mass of the object. D It can decrease the amount of force needed to move an object.

A. Work is the product of force times distance. A simple machine can increase the distance the object travels or decrease the amount of force needed. D. Work is the product of force times distance. A simple machine can increase the distance the object travels or decrease the amount of force needed.

How does heat from the sun travel to the Earth? A by the process of photosynthesis B by the process of conduction C by the process of radiation D by the process of convection

C. Heat from the sun reaches Earth by the process of radiation.

Which of the following must be present in large quantities in order for fossil fuels to be created? A carbon dioxide B organic matter C coal D pollutants

B. Fossil fuels form from organic matter: the remains of dead organisms.

Jason was holding a ball and then threw it to Tommy, who caught the ball and held it in his glove before throwing it back. Which of the following is the most accurate statement about energy as the boys played catch? A The ball had kinetic energy while moving, but the energy disappeared when the ball was caught. B The ball had kinetic energy while moving, which transformed into heat and sound when caught. C The ball had potential energy while in the boys' gloves, which transformed into kinetic energy after the ball was moving. D The ball had potential energy while in the boys' gloves, but only kinetic energy while moving.

B. In this situation, the ball's kinetic energy is due to its motion and the ball's potential energy is due to its height above the ground. Assuming the two gloves are at the same height, the kinetic energy does not transform into potential energy, but into sound and heat (or thermal energy in the glove and ball) each time the ball is caught.

Metal cooking utensils often have wooden handles. Which property of wood makes it a good material for the handle on a cooking tool? A Wood and metal create a chemical reaction. B Wood is a poor conductor of heat. C Wood is a renewable resource. D Wood absorbs more bacteria than metal.

B. The electrons of wood, glass, plastic, and air are examples of materials that have electrons which stay close to the nucleus of the atom making them poor conductors of heat and electricity. These poor conductors of heat and electricity are used as insulators. Insulation is the positive factor that makes wood a good tool for cooking.

Which of the following energy transformations occurs when wood burns? A mechanical energy into light energy B chemical energy into thermal energy C electrical energy into thermal energy D nuclear energy into mechanical energy

B. When wood burns, chemical energy stored in atomic bonds is converted into heat energy.

Mr. Harris, a second-grade teacher, wants to demonstrate the use of a lever to his students. Which of the following would be the best piece of equipment at his school for Mr. Harris to use? A a beaker B a glass slide C a seesaw D a cafeteria table

C. A lever is a beam resting on pivot point to reduce the force required to move a load. A seesaw is a great example.

A small amount of a substance is added to a solution in a beaker. A reaction occurs when the materials are combined, causing the solution to cool. Which kind of reaction took place? A isobaric B nonspontaneous C endothermic D exothermic

C. A reaction which absorbs heat from the surroundings, in this case from the solution, is endothermic.

Mario watches his friends run the relay at a high school track meet on a warm, Friday afternoon. Jack was at the starting line, ready to take off. The starting gun boomed and Jack took off. Jack ran his part of the relay and handed his wooden baton off to Azrial, who ran and handed the baton to Juan. Roberto finished the last stretch of the race. Which type of energy was least likely to have been a part of the race? A thermal B kinetic C chemical D magnetic

C. Although electromagnetic energy from the sun and heat were a part of the afternoon, magnets were not involved in the race.

Which of the following is the principal type of energy is stored in a AA battery? A heat energy B gravitational potential energy C chemical potential energy D mechanical energy

C. Chemical energy is energy stored in the bonds of a chemical compound. The breaking of the chemical bonds releases energy. In a battery, energy in the chemical bonds becomes electric potential energy.

A teacher is teaching a unit on weather to the class. As a demonstration, the teacher heats a beaker on a hot plate and adds blue food coloring to the water. The students observe the movement of coloring in the water. Which of the following processes is best demonstrated by the movement of the food coloring? A evaporation B conduction C convection D radiation

C. Convection is the process of heat transfer by currents in fluids, which is observed in the teacher's experiment.

Marta holds a cup of hot chocolate in her hands. Select the true statement about Marta and the coffee. A The cup of hot chocolate delivers thermal energy to Marta's hands. B The cup of hot chocolate delivers nothing to Marta's hands, it just warms them. C The cup of hot chocolate delivers heat to Marta's hands. D The cup of hot chocolate delivers its temperature to Marta's hands.

C. Heat is the energy transferred from a hot object to a cooler object.

Heat is NOT a form of energy present in a pot of hot coffee. Which statement best explains why not? A Nonsense! Heat IS a form of energy in the coffee because the coffee is hot. B The coffee is made from boiling water, so the water contains the heat. C Heat refers to the transfer of energy, so it is not in the coffee itself. D Heat transforms into chemical energy while the coffee is brewing.

C. Heat refers only to the energy that is transferred from a hot object to a cold object. Thermal energy is the name for the energy in an object because of its temperature.

A swimming pool heats up during the day and cools off at night. Which is the primary type of heat transfer that warms the pool? A conduction B thermal energy C radiation D convection

C. Radiation from the sun is the primary type of heat transfer that heats the pool.

What is the formula for work? A work = energy x force B work = density + force C work = force x distance D work = force x density

C. The formula for work = force x distance.

Which of the following factors most affects an object's capacity for thermal energy? A color B surface area C mass D reflected light

C. Thermal energy capacity is dependent upon qualities like the object's mass, water content, and temperature.

Energy can be transformed from one type to another. What type of energy transformation is most likely occurring when you turn on a light switch? A potential to chemical B chemical to kinetic C electrical to light D heat to mechanical

C. When you turn on a light switch, you are completing a circuit which is transferring electrical energy into light energy.

There are a few common ways energy can be stored: ........ energy is stored in chemical bonds. For example, ....... potential energy is stored in every carbon-carbon bond of carbohydrates.

Chemical

.......burn fuel, transforming chemical energy into heat and then into mechanical energy. For example, the motor in a car uses fuel to heat and expand air, which moves the pistons in the engine up and down. The pistons turn the crankshaft and eventually move the car.

Combustion motors

..... is the transfer of thermal energy through a solid or between two materials that are touching. The heat energy moves from a hotter region to a colder region until the temperature has equalized. Putting the tip of a metal spoon in a flame will eventually make the entire spoon hot.

Conduction

........ of energy states that in a closed system, energy is conserved, so at all times the total amount of energy in a system is constant, even if it changes form or moves from one place to another. In other words, the total amount of energy present before an event equals the total amount of energy present after the event.

Conservation

...... is the transfer of heat by a moving fluid, like air or water. A fluid expands when it is heated. As it expands, it becomes less dense and is forced up by the cooler, more dense fluid surrounding it. The rising fluid carries thermal energy upward. Convection drives wind and water currents. A greenhouse blocks convection. As sunlight streams in and heats the air in the greenhouse, the air rises, but hits the ceiling. The air cannot escape to carry the heat higher into the atmosphere, so the greenhouse continues to get warmer and warmer. Many homes are warmed by convection as warm air is blown into the living spaces from the furnace.

Convection

Casey is playing with her yo-yo. She performs an "around the world" trick, in which the yo-yo travels up and around in a circle before returning to her hand. At which point in its circular path would the yo-yo have the least potential energy? A when the yo-yo is at the rear-most point of its circular path B when the yo-yo is at the top of its circular path C when the yo-yo is at the forward-most point of its circular path D when the yo-yo is at the bottom of its circular path

D. Gravitational potential energy increases as the object gets farther away from the ground. Since the yo-yo is closest to the ground at the bottom of its path, that is the location where it has the least potential energy.

A pendulum swings back and forth in a vertical semicircle pattern. When does the pendulum have its greatest potential energy? A when the pendulum starts to move downward B when the pendulum is at the bottom of the arc C when the pendulum starts to move upward D when the pendulum is at the top of the arc

D. Potential energy is the energy stored in an object by virtue of an object's position relative to other objects. At the top of the arc the pendulum has its maximum height, therefore it has its maximum potential energy.

Compared with the thermal energy and temperature of a the sand on a city beach, very hot cup of hot chocolate has: A a greater thermal energy but a lower temperature. B a greater thermal energy and a higher temperature. C a lower thermal energy and a lower temperature. D a lower thermal energy but a higher temperature.

D. The average kinetic energy (temperature) of the molecules in the cup of hot chocolate is greater than the average kinetic energy of the molecules in the sand, so the hot chocolate has the higher temperature. However, the hot chocolate has far fewer molecules than the sand, so holds less thermal energy.

There are a few common ways energy can be stored: ...... potential energy is the energy stored due to elasticity. For example, a stretched spring has elastic potential energy.

Elastic

....... is the ability to do work or apply a force that moves something through a distance.

Energy

........ were formed from the remains of long-dead plants, which had captured the sun's energy through photosynthesis when they were alive. Under immense pressure and heat in the earth, these remains are slowly cooked into what we call fossil fuels. Coal formed from land plants, while oil formed from marine organisms. Natural gas is found above and around both types because it is a byproduct of coal and oil formation.

Fossil fuels

There are a few common ways energy can be stored: ....... potential energy is the energy an object has because of its height (the ability for gravity to pull it down). For example, a skier on top of a hill has gravitational potential energy.

Gravitational

..... occurs through three different processes: conduction, convection, and radiation.

Heat transfer

........ is collected as gravity pulls water from higher elevations to lower elevations. The falling water turns a turbine that converts the kinetic energy of the water into electrical energy in a generator. In a similar manner, windmills generate electricity by using the wind's kinetic energy to turn the blades, which run a generator to convert the kinetic energy into electricity. Other alternative sources of energy include geothermal energy, tidal energy, energy from biomass, and nuclear energy.

Hydroelectric energy

....... energy is the energy of motion. Anything that is moving has kinetic energy.

Kinetic

.... energy involves moving. ..... energy is stored up.

Kinetic Potential

...... energy is stored energy. ..... energy is associated with the position or distance between objects.

Potential

...... is the transfer of heat by an electromagnetic wave. Electromagnetic waves are a combination of vibrating electric and magnetic fields. The sun radiates electromagnetic waves, many of which are absorbed by matter on the earth. The energy in electromagnetic radiation causes the particles it strikes to vibrate more rapidly.

Radiation

......... take advantage of the relationship between force and distance. They allow a person to do the same amount of work but reduce the force needed by increasing the distance over which the force is applied.

Simple machines

...... is a measure of the average of the kinetic energy of each particle in the substance.

Temperature

While ..... can be transformed or transferred, it is always conserved. You can't destroy energy, but you do "lose" it as work and heat.

energy

Generators and turbines work together to transform energy. ..... first transform energy into kinetic energy. For example, fossil fuels are burned to heat water and the resulting rising steam turns blades, capturing it as kinetic energy. The generator then turns this rotating kinetic energy into electrical energy.

Turbines

In an ..... process, a substance absorbs energy. Evaporation is an endothermic process. As heat is transferred from a person's hot body into the sweat (liquid water) on their skin, their body cools. As the water particles in the sweat absorb energy, they speed up. Some particles move fast enough to evaporate and escape as a gas.

endothermic

In the metric system, the unit for ..... is the joule (J). In US customary units, the unit for energy is the foot-pound (ft⋅lb).

energy

Interestingly, .... occurs at any temperature between the melting point and boiling point. This is because temperature is the average kinetic energy of the particles. Some particles are moving very slowly, others are moving very fast, while most are moving at speeds somewhere in between. The particles moving the quickest have enough energy to escape as a gas, or evaporate.

evaporation

In an ........... process, a substance loses energy. Condensation is an exothermic process. When water vapor (a gas) touches a cold window, some of the thermal energy in the water vapor transfers to the window as heat. The cooling gas particles move closer together and slow down, condensing to liquid water on the window.

exothermic

Burning fossil fuels also causes air pollution, including ....... like carbon dioxide and methane, that contribute to global warming. Other pollutants from fossil fuel are sulfur and nitrogen oxides, which create .......

greenhouse gases acid rain

-For example, consider a girl jumping off a diving board into a pool and stopping deep in the water. This process has two "events". Event 1: Girl jumping off a diving board. Define the girl as the entire system. The girl starts with some gravitational potential energy, say 650 J, high up on the diving board, and 0 J of kinetic energy. When the event ends, just as she starts to hit the water, she is moving fast. She now has 0 J of potential energy and 650 J of kinetic energy. In this event, we ignore any friction from the air. -The girl's total energy high up on the board transforms from potential to kinetic energy as she falls to the water. None of the energy disappears. Event 2: Girl stopping deep in the water. Define the girl and the water surrounding her as the system. Just as the girl hits the water, she has 650 J of kinetic energy. After she enters the water, friction forces in the water stop her. When she stops, she has 0 J of kinetic energy, but she and the water have gained 650 J of thermal energy. All of the kinetic energy of the girl's motion transforms into thermal energy as she stops. None of the energy disappears.

read

Alternative sources of energy are being developed as long-term (............), less polluting solutions to the rapid use of fossil fuels. ......, which is electromagnetic radiation from the sun, is constant and abundant. Solar heaters collect energy from the sun and convert it to heat. These can be as simple as big black pads that heat water passing underneath, or as complex as a set of mirrors that collect and direct sunlight to a central tower that gets heated to over 1000°F. Photovoltaic solar panels collect sunlight and turn it into electricity.

renewable resources Solar energy

Instead, in a mechanical system, the ...... of an object's potential and kinetic energy is often called mechanical energy. KE + PE = ME

sum

For example, a hot tub full of water at 102°F will have more ..... energy than a cup of coffee at 150°F because there are a lot more particles of water in the hot tub

thermal

The total energy of all of the particle motion in a substance is its ..... energy, a form of kinetic energy.

thermal

Energy can also be ........, or moved, from one object to another. For example, when a baseball bat strikes a baseball, some of the bat's kinetic energy is transferred to the ball.

transferred

Examples of energy ..... include: -wind energy (kinetic) transformed into mechanical energy by a turbine and then electrical energy by a generator -solar energy (light) transformed into heat as it strikes black asphalt -electrical energy transformed into kinetic energy by the motor of an electric fan -chemical energy transformed into heat, or vice versa, during a chemical reaction

transformation

Energy can be ........ (converted from one form to another). For example, when a ball rolls down a hill its gravitational potential energy transforms into kinetic energy.

transformed

The term "......." is used to describe the amount of energy it takes to move an object. Since energy is conserved, the force doing the work uses as much energy as is given to the object and its surroundings. Work is calculated by multiplying the force applied to an object times the distance the object moves: work = force ∙ distance

work