Model two objects interacting through a gravitational, electric, or magnetic field, and describe how the energy stored in the field changes as the objects move closer or farther apart (MA STE Introductory Physics, Energy, HS-PS3-5).

What this topic is asking

The Massachusetts framework asks you to think about energy not just for single objects but for two objects interacting through a field. Standard HS-PS3-5 wants you to model two objects interacting through a gravitational, electric, or magnetic field and describe how the energy stored in the field changes as they move closer or farther apart. The crosscutting idea is energy and matter together with cause and effect: a field both exerts a force and stores energy, and moving the objects changes how much energy the field holds.

A field stores energy

Modules 2 and 6 treat fields as the source of forces (gravity, the electric force, the magnetic force). This topic adds the energy side: those same fields store energy. The MCAS wants you to model a pair of objects and reason about how the stored energy rises and falls as they move, using bar charts, diagrams, or words rather than heavy formulas.

Moving against the force stores energy

The pattern is the same in all three fields:

• Gravitational. Lifting an object higher does work against gravity and stores gravitational potential energy. The reference-sheet formula $PE = mgh$ captures this: more height means more stored energy.
• Electric. Pulling two opposite charges apart (they attract) does work against the attraction and stores electric potential energy. Pushing two like charges together (they repel) also stores energy.
• Magnetic. Pushing two like poles together against their repulsion stores energy in the magnetic field.

Moving with the force releases energy

This is the release side of the same idea, and it ties straight back to conservation of energy. When a dropped object falls, the gravitational field energy of the object-Earth system decreases and the object's kinetic energy increases by the same amount. When two repelling magnets are released, the magnetic field energy decreases and the magnets gain kinetic energy. The field is the store; motion is the payout.

Worked example

Reference-sheet note

The reference sheet prints gravitational potential energy as $PE = mgh$, the one field-energy formula you calculate with on this test. The electric and magnetic field-energy changes are handled qualitatively: you describe whether the stored energy increases or decreases as the objects move, and where the released energy goes. What you recall is the rule, working against the force stores energy, moving with the force releases it, and the total is conserved.

Try this

Q1. State what happens to the energy stored in the gravitational field when an object is lifted higher. [1]

• Cue. It increases, because lifting does work against gravity; this stored energy is the gravitational potential energy $mgh$.

Q2. Two like magnetic poles are pushed together and held, then released. Describe the energy changes. [2]

• Cue. Pushing them together stores energy in the magnetic field; on release, that stored energy is transformed into kinetic energy as the magnets fly apart.