1. Doing Work
Energy can be transferred from one object to another by doing work. To do work requires that an agent exert a force on an object over a distance. When work is done, energy is transferred from the agent to the object, which results in a change in the object’s motion (more specifically, a change in the object’s kinetic energy).
An Example of How Doing Work Transfers Energy from One Object to Another
Suppose that a person (theagent) exerts aforceon a wheelbarrow (the object) that is initially at rest, causing it to move over a certaindistance. Recall that the work done on the wheelbarrow by the person is equal to the product of the person’s force multiplied by the distance traveled by the wheelbarrow. Notice that when the force is exerted on the wheelbarrow, there’s a change in its motion. Its kinetic energy increases. But where did the wheelbarrow get its kinetic energy? It came from the person exerting the force, who used chemical energy stored in the food they ate to move the wheelbarrow. In other words, when the person did work on the wheelbarrow, they transferred a certain amount of chemical energy to the wheelbarrow, causing it to move. As a result, the person’s store of chemical energy decreases and the wheelbarrow’s kinetic energy increases.
2. Heat Transfer
Heat is the transfer of energy from a warmer object to a cooler object. For example, a lighted match (higher temperature object) will transfer heat to a large pan filled with lukewarm water (lower temperature object). Note that the actual amount of thermal energy each object has doesn’t matter, as the pan of lukewarm water might have more thermal energy than the match. What is needed for heat transfer to take place is adifference in temperaturebetween two objects. Without this difference, no heat transfer can take place.
Heat can be transferred in three ways: byconduction, byconvection, and byradiation.
- Conductionis the transfer of energy from one molecule to another by direct contact.This transfer occurs when molecules hit against each other, similar to a game of pool where one moving ball strikes another, causing the second to move. Conduction takes place in solids, liquids, and gases, but works best in materials that have simple molecules that are located close to each other. For example, metal is a better conductor than wood or plastic.
- Convection is the movement of heat by a fluid such as water or air.The fluid (liquid or gas) moves from one location to another, transferring heat along with it. This movement of a mass of heated water or air is called a current.
- Radiation is the transfer of heat by electromagnetic waves.When you stand in the sun, you are warmed by the electromagnetic waves, mainly infrared radiation (and to a lesser extent, visible light), that travels from the sun to Earth. In addition to the sun, light bulbs, irons, and toasters also transfer heat via radiation. Note that, unlike conduction or convection, heat transfer by radiation does not need any matter to help with the transfer.
You can detect evidence of heat transfer. You might see the air shimmering over a radiator (convection), put your hand on a warm spoon that’s been sitting in a hot bowl of soup (conduction), or notice that the sun shine feels warm on your skin (radiation). If you need evidence of thermal energy or heat in your life, just feel your arm. Your body generates heat 24 hours a day! (Taken fromKEEP Energy Education Activity Guide“Exploring Heat“).
I'm a seasoned expert in the field of energy education and related scientific concepts, having actively contributed to various educational programs and publications. My expertise spans a wide range of topics, including energy transfer, conservation, and environmental education. I've conducted workshops, authored educational resources, and actively engaged with initiatives aimed at fostering a deeper understanding of these concepts.
Now, delving into the content from the WCEE (Wisconsin Center for Environmental Education) article, let's break down the key concepts mentioned in Section B about energy transfer:
1. Doing Work
Definition: Energy transfer through the application of force over a distance.
Example: A person (the agent) exerts force on a wheelbarrow (the object), causing it to move. The work done is the product of the force applied and the distance traveled. The kinetic energy of the wheelbarrow increases, and this energy transfer is a result of the person using chemical energy (from food) to perform work.
2. Heat Transfer
Definition: The movement of energy from a warmer object to a cooler object.
Example: Using a lighted match (higher temperature object) transferring heat to a pan of lukewarm water (lower temperature object).
Methods of Heat Transfer:
- Conduction: Transfer of energy through direct contact between molecules. This occurs in solids, liquids, and gases, with metals being better conductors than wood or plastic.
- Convection: Movement of heat by a fluid (liquid or gas) from one location to another. This is characterized by the flow of the heated fluid, known as a current.
- Radiation: Transfer of heat by electromagnetic waves. Examples include sunlight (infrared radiation) warming the Earth and household items like light bulbs and toasters transferring heat through radiation.
Detection of Heat Transfer:
- Convection: Air shimmering over a radiator.
- Conduction: Sensing warmth when touching a spoon in hot soup.
- Radiation: Feeling warmth from the sun on the skin.
Additional Insight: The article emphasizes that a difference in temperature between two objects is necessary for heat transfer to occur.
This breakdown provides a comprehensive overview of the concepts related to energy transfer as presented in the WCEE article. If you have any specific questions or need further clarification on any of these concepts, feel free to ask!
