Lesson 1 Energy Flow in Technological Systems
Evidence for the Presence of Energy
It is important to be able to recognize that energy is present. How can you do this?
C1.17 Campfire
What evidence can we look for to determine if energy is around us?
We looked at the common forms of potential and kinetic energy at the start of this lesson. Some forms of energy can be seen or felt directly.
We looked at the common forms of potential and kinetic energy at the start of this lesson. Some forms of energy can be seen or felt directly.
A physical change
is a change to a substance that may either require energy or release energy. When a physical change occurs, the energy involved is usually in the form of thermal energy (heat). The energy changes involved in physical changes can be difficult
to detect.
C1.18 Boiling water in a kettle
Melting a solid, boiling a liquid, and the evaporation of a liquid to gas are physical changes that require energy. You may feel the thermal energy from the sun that evaporates water off of a lake or the thermal heat from a stove element
that is needed to boil a pot of water to cook pasta. Perhaps you see the steam coming from a kitchen kettle as you boil water for tea.
Condensing gas to a liquid and freezing a liquid to a solid are physical changes that release energy. You may feel the thermal energy in the back coils of your refridgerator that is from the cooling of the interior of the appliance
or see the condensation droplets of water on the glass of a cold drink left outside in the sun.
C1.19 Condensation of water on a cold glass
A chemical change is a change to a substance that may either require
energy or release energy. When a chemical change occurs, the energy involved can be in a number of different forms and there are many common indicators that a chemical change has occurred.
C1.20 Matchstick burning
Has a gas been given off? You can usually tell this by bubbles forming or vapour being produced.
A colour change may occur. Is the new substance a different colour?
A colour change may occur. Is the new substance a different colour?
Heat may be absorbed or released. Is the new substance that is produced warmer or colder?
Has light been given off? This one is an easy one to detect!
Has a solid, called a precipitate, been formed as a new substance?
Has light been given off? This one is an easy one to detect!
Has a solid, called a precipitate, been formed as a new substance?
Changes other than chemical and physical changes are also important to recognize as evidence for the presence of energy.
Has the object changed shape? Has it expanded, contracted, or deformed?
Has the object increased or decreased in temperature?
Has the object sped up, slowed down, changed direction, started to move, or come to a stop? These questions in particular will lead us into the next lesson.
Has the object changed shape? Has it expanded, contracted, or deformed?
Has the object increased or decreased in temperature?
Has the object sped up, slowed down, changed direction, started to move, or come to a stop? These questions in particular will lead us into the next lesson.
C1.22 Blurred motion of a train
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned about. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your
responses (where necessary) to study from.
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Why is it important to recognize that energy is present?
When you can identify that energy is present, you can gain a better understanding of the system you are looking at and identify whether any changes in energy are occurring.
- What are the ways to recognize that energy is involved due to a physical change?
Physical changes may require energy (where thermal, electrical, solar energy is provided) or may release energy (in the form of thermal energy usually). It is just a change in state of matter.
- What are the ways to recognize that energy is involved due to a chemical change?
Chemical changes may require energy (where thermal, electrical, solar energy is provided) or may release energy (in the form of thermal energy or light). Look for the common indicators of a chemical reaction, such as a gas being produced,
a colour change, temperature increases or decreases, light given off, or a precipitate produced.