Define physical changes based on property alterations without new substance formation, and evaluate their reversibility.
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Hook on the concept of reversing a change.
Hook introducing physical change using paper.
Imagine you have a blank piece of paper. If you fold it into a delicate origami crane, it looks completely different. But if you were to carefully unfold it, you'd still have that exact same piece of paper.
However, if you set that same paper on fire, it turns into ash and smoke. You can't get the paper back.
Folding the paper is a change in disguise—the appearance changes, but the material itself remains exactly the same!
Explanation of physical properties and changes.
Before we define a physical change, we need to know what a physical property is. These are the characteristics of a substance that you can easily observe or measure, such as its shape, size, and state (solid, liquid, or gas).
Visual examples of physical changes.
Crushing, inflating, and melting alter size, shape, and state—but create no new substances.
Identify which scenario represents a physical change.
Which of the following processes is an example of a physical change?
Explanation of reversible and irreversible changes.
Once something has undergone a change, can we get it back to its original form? Physical changes can be grouped into two main categories based on this simple question: reversible and irreversible.
Visual comparison of reversible and irreversible physical changes.
Melting can be reversed by freezing. Chopping cannot be undone.