Enduring Understandings

• We do not observe energy, we observe the effects of energy.
• Energy is transformed from one form to another during changes in matter.
• The amount of energy before a transformation is equal to the amount of energy after the transformation.
• An object's momentum accounts for both mass and velocity.
• An object's momentum will be changed when a force is applied. The amount of change will depend on (1) the magnitude of the force and (2) the amount of time over which the force is applied.
• Electric charges can either be positive or negative. Like charges repel each while opposite charges attract each other.
• The flow of electricity involves three key measurements: Voltage causes the charges to move from one location to another, current describes the rate at which the charges move, and resistance characterizes the degree to which a material opposes the flow of the charges.
• Waves carry energy from one place to another.
• Sound energy is transported by a mechanical wave that requires a physical medium (i.e air).
• Light energy is transported by an electromagnetic wave that can travel through a vacuum.
• The electrons that surround a nucleus gain and lose energy by absorbing or releasing photons of specific wavelengths.
• Radioactive particles and waves can also be absorbed or released by the nucleus of an atom. These processes, however, involve much more energy than those involving electrons.