NGSS HS-PS2-2
The Standard
Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.
Next Generation Science Standards
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students use mass and signed velocity to calculate momentum for two objects moving along one line. They compare total momentum before and after an interaction, then use the results to support a claim about the system.
What Mastery Looks Like
- Students correctly calculate each object’s signed momentum before and after an interaction. They show equal system totals and explain that momentum transfers between objects when external forces are negligible.
Common Misconceptions
- Students often add speeds without assigning positive and negative directions. They may think each object keeps its own momentum, rather than the two-object system keeping the same total. They may also assume kinetic energy is conserved in every collision.
How to Assess It
- Give this exit ticket: A 2 kg cart moving at +3 m/s hits a 1 kg cart moving at -2 m/s. If the first cart ends at +1 m/s, find the second cart’s final velocity and verify total momentum.
Lesson moves
Ways to Teach It
Measure cart masses, film a one-dimensional collision, record before-and-after velocities, and compare total signed momentum.
Ask students to write: "How can one cart lose momentum while the two-cart system keeps the same total?"
Sort collision cards into matching before-and-after pairs using mass, signed velocity, and total momentum.
Analyze a bumper-car collision by choosing a positive direction and calculating each car’s momentum before and after impact.
Free download
Printable HS-PS2-2 Worksheet
A ready-to-print activity worksheet aligned to HS-PS2-2, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
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Where This Standard Sits
See the whole path on the Physical Science progression map.
Before This Standard
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