Energy is one of those units that looks easy on paper and then quietly falls apart in week two. Students can recite "energy cannot be created or destroyed" on day one, but ask them where the kinetic energy of a skidding cart went and you get blank stares. The definition is not the hard part. The accounting is.
This post lays out the 3.5-week energy unit we use in our full-year physics curriculum, where energy sits sixth in the sequence: Motion, Forces, Momentum, Gravity, Electrostatics, Energy, Circuits, Waves. That placement matters. By the time students hit energy, they are comfortable with velocity, forces, and momentum, which means you can connect energy back to earlier units instead of teaching it in a vacuum. The unit targets NGSS HS-PS3-1, HS-PS3-2, and HS-PS3-3.
Why Energy Comes Sixth, Not First
Some curricula front-load energy because it feels foundational. In practice, energy is an abstraction built on top of other abstractions. Work is force times displacement, so students need a solid grasp of forces. Kinetic energy depends on velocity squared, so they need kinematics. And the best capstone problem in the unit, the ballistic pendulum, requires conservation of momentum, so momentum has to come first.
Sequencing energy after momentum also lets you attack the single most persistent confusion in mechanics: the difference between momentum and kinetic energy. More on that below.
The 3.5-Week Sequence at a Glance
Here is the day-by-day skeleton. Adjust for your bell schedule, but the ordering is the important part.
Week 1: Work and Energy
- Days 1 and 2: What work means in physics, and why carrying a backpack across the room at constant height is not work. Work as force times displacement, positive and negative work.
- Days 3 and 4: Kinetic energy, and the work-energy relationship. Students calculate work done on an object and connect it to the change in kinetic energy.
- Day 5: Practice day with the GUESS method (Given, Unknown, Equation, Substitute, Solve). Every quantitative problem in this unit runs through the same five steps, which keeps struggling students from freezing at the "where do I start" stage.
Week 2: Potential Energy and Conservation
- Days 1 and 2: Gravitational potential energy. Height is relative, so spend real time on choosing a reference point. This is where a lot of quiet errors are born.
- Days 3 and 4: Conservation of energy. Introduce energy bar charts here (see the next section) before any equations. Then formalize: total energy before equals total energy after, with thermal energy as the ledger line that catches what friction takes.
- Day 5: Quiz on work, kinetic energy, and potential energy, followed by a conservation exploration with household materials (details below).
Week 3: Thermal Energy and Velocity Equations
- Days 1 and 2: Kinetic and thermal energy together. Friction does not destroy energy; it converts it. Students should be able to say where the energy went, not just that "some was lost."
- Days 3 and 4: Velocity equations from conservation of energy. Solving for final speed at the bottom of a ramp or the top of an arc. This is where scientific notation, which students have had since around week 10 of the year, starts earning its keep on larger numbers.
- Day 5: Mixed practice. Warm-ups from our physics warm-ups collection work well here as spiral review of earlier weeks.
Week 4 (Half Week): The Ballistic Pendulum Capstone
- Days 1 and 2: The ballistic pendulum, the problem that fuses this unit with the momentum unit. A projectile embeds in a hanging block: momentum is conserved during the collision, then energy is conserved during the swing. Students have to know which principle applies to which phase, and why kinetic energy is not conserved in the collision itself.
- Day 3: Review and unit test.
Why Energy Bar Charts Beat Formula-First Teaching
The temptation with energy is to hand students the conservation equation on day one and start plugging in numbers. Resist it.
Energy is fundamentally an accounting problem. Before students touch an equation, they should be able to draw a bar chart of a system's energy at two moments in time: this much kinetic, this much potential, this much thermal, and the totals match. When the bars balance, the equation writes itself. When students skip the bars and go straight to formulas, they produce answers like a cart gaining speed while also gaining height with no energy input, and they do not notice anything is wrong because the algebra worked.
The bar chart forces the conceptual question first: where is the energy now, and where does it go. The formula then becomes a translation of a picture the student already believes, rather than a string of symbols to be satisfied. It also makes thermal energy visible. Friction stops being a mysterious subtraction and becomes a bar that has to appear somewhere for the books to balance.
Formula-first students can pass a quiz. Bar-chart-first students can catch their own mistakes. That is the difference you are buying with two extra days of conceptual work.
The Two Misconceptions That Will Eat Your Unit
"Energy gets used up"
Students arrive with an everyday meaning of energy: it runs out, like a phone battery. So when a block slides to a stop, they will tell you its energy is gone. The fix is relentless accounting. Every time something slows down, ask where the energy went, and do not accept "it was lost." It went to thermal energy in the surfaces. The bar chart makes this concrete: the kinetic bar shrinks, the thermal bar grows, the total never changes.
Kinetic energy versus momentum
This is the big one, and it is exactly why the ballistic pendulum belongs at the end of this unit. Both quantities depend on mass and velocity, so students treat them as interchangeable. They are not. Momentum is conserved in every collision; kinetic energy is only conserved in elastic ones. A hypothetical worth posing to your class: two objects with equal momentum can have wildly different kinetic energies if their masses differ, since kinetic energy depends on velocity squared. Working that comparison as a GUESS problem, side by side, does more than any lecture on the distinction.
The ballistic pendulum forces students to hold both ideas at once. Use momentum for the embedding collision, then energy for the swing. Students who try to use energy conservation across the collision get the wrong answer, and the wrongness is the lesson.
A Conservation Exploration With Household Materials
You do not need a track system to make conservation visible. A pendulum built from string and a washer, taped to a doorframe or lab stand, is enough. Have students release the washer from a measured height and observe that it returns to nearly, but never quite, the same height. That "never quite" is the entry point for thermal energy and air resistance, framed as an accounting question: the books have to balance, so where did the missing height go.
Extend it with a marble and a homemade ramp of foam pipe insulation cut lengthwise. Students predict the marble's speed at the bottom using conservation of energy, then check it by measuring horizontal launch distance off a table. The gap between prediction and measurement is not a failure; it is the friction term, measured. If you want fully structured versions of investigations like these with data tables and analysis questions built in, our labs collection has ready-to-run options.
Assessment Cadence
Spread assessment across the unit rather than betting everything on the test:
- Daily warm-ups as spiral review, two to five minutes at the bell.
- A quiz at the end of week two covering work, kinetic energy, and potential energy, before conservation problems get layered on top.
- A review day before the unit test. A structured review game beats a worksheet packet here, because it surfaces misconceptions out loud where you can address them. Our review games collection covers this format.
- The unit test, with the ballistic pendulum as the culminating multi-step problem.
Every quantitative item, from warm-up to test, uses the same GUESS structure, so the method itself is never the obstacle.
Get the Full Unit, Ready to Teach
Everything above is the plan. Building the daily materials, the notes, practice sets, labs, quizzes, review game, and test, is the part that consumes a teacher's weekend. If you would rather spend that time teaching, the complete energy unit has every day of this sequence ready to print, and it slots directly into the full-year curriculum if you want the whole sequence from Motion through Waves.