Year 9 Science · Unit 3 · Lesson 5
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Learning Goals
Real-world context
In January 2020, lightning strikes ignited hundreds of fires across New South Wales and Victoria during the Black Summer bushfires. A single lightning bolt strikes a gum tree in the Blue Mountains: the electrical energy in the bolt discharges in milliseconds, splitting the tree and igniting the dry bark. Flames spread outward through the surrounding bush, releasing enormous quantities of energy in multiple forms at once.
(a) When the lightning bolt strikes the tree, it releases energy as light, sound, and thermal energy. What was the original form of energy in the lightning bolt, and where did it come from before the strike?
(b) Once the gum tree ignites, chemical energy stored in the wood is released. List three forms of energy that are produced as the tree burns, and describe what evidence you would observe for each one.
Read the graph
The bar chart below shows the approximate percentage of the body's daily energy budget used by each major organ in an adult human at rest.
Data: Adapted from Mink et al. (1981) Journal of Neurological Sciences; Rolfe & Brown (1997) Physiological Reviews
(a) Which organ uses the most energy, and which uses the least? What is the difference in percentage between them?
(b) The heart and kidneys both use 7% of the body's energy. Predict which would increase its energy use more during vigorous exercise, and explain why using the concept of energy transformation.
(c) The brain uses 20% of the body's energy even at rest, far more than its mass would suggest. Using lesson content, explain why the brain demands so much chemical energy even when you are not doing anything active.
Wrap Up
In one sentence, what was the main idea of this lesson?