• Energy cannot be directly seen or measured.
• All moving objects have motion energy.
• Speed is the indicator of how much motion energy an object has. If an object’s speed increases or decreases, its motion energy has increased or decreased.

Colliding balls

Quick Check

• Energy can move from one object to another object; this is called energy transfer.
• Motion energy can be transferred between objects through pushes, pulls, hits, or collisions. Stronger interactions (e.g., bigger hits) transfer more motion energy.
• Energy changes take place in multiples; whenever there is a loss of energy somewhere, there must be a gain in energy somewhere else (and vice versa).
• A drawing or representation (such as energy bars) can show changes in the amount of energy an object has.

• An elastic object is any object that returns to its original shape after being deformed (bent, twisted, stretched, squeezed, etc.)
• Deformation of an elastic object is the indicator of the object’s elastic energy. If an elastic object’s deformation increases or decreases, its elastic energy has increased or decreased.
• When energy changes from one form to another, this is called energy transformation.
• Motion energy can be transformed into elastic energy (and vice versa).

• Energy cubes can be used to reason about energy flows and forms.

Rubber band and propeller

Wrap Up Probe

• The Energy Tracking Lens questions, “Where does the energy come from?” and, “Where does the energy go?” provide a useful way of thinking about energy flow in any scenario.
• Drawings and representations help reason about energy flow and transformation in a scenario.