Energy is what it takes to make things happen: to set things moving, to lift them, to light them up, to warm them, to make them sound. Nothing goes, glows, or grows without energy being spent on it — and whatever is doing the spending must first have energy to spend.
Examples
Example 29.5 (Forms of energy)
Energy shows itself in different forms: motion energy in the rolling ball and the blowing wind; light energy pouring from lamp and Sun; heat energy in everything warm; electrical energy traveling through wires; stored energy waiting quietly in food, fuel, springs and lifted things. Same something, many forms.
Example 29.8 (Chains everywhere)
Your morning ride, traced: breakfast (store) your muscles (converter) motion of the bicycle warmth (you feel it — you glow). The wind farm: moving air turning blades electrical energy in the wires light in your lamp tonight. The dam: high water falling water spins the turbines electrical energy. Long chains are just short ones linked: form after form after form.