Module: Conservation of Momentum
DCI: PS2.A (C) If a system interacts with objects outside itself,
the total momentum of the system can change; however, any such change is
balanced by changes in the momentum of objects outside the system.
PE: HS-PS2-2 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.
HS-PS2-3 Apply scientific and engineering ideas to design,
evaluate, and refine a device that minimizes the force on a macroscopic object
during a collision.
[Clarification
Statement: Emphasis is on the quantitative conservation of momentum in
interactions and the qualitative meaning of this principle.] [Assessment
Boundary: Assessment is limited to systems of two macroscopic bodies moving in
one dimension.]
[Clarification
Statement: Examples of evaluation and refinement could include determining the
success of the device at protecting an object from damage and modifying the
design to improve it. Examples of a device could include a football helmet or a
parachute.] [Assessment Boundary: Assessment is limited to qualitative
evaluations and/or algebraic manipulations.]
The ideas here are:
- in a system interacting with objects outside itself, the total momentum of the system can change
- any changes to the momentum of the system are balanced by changes in the momentum outside the system
Again, we are using the formula for momentum to prove that momentum is conserved when there is no net force acting on the system. We covered this in a previous batch, so only one or two questions of this nature are necessary here. The rest of this batch should focus on the second PE. In order to do that, we might describe a device (football helmet, parachute) that is designed to minimize the force acting on an object, as well as provide some data about how that device functions. Then, we can ask students to propose a modification to the design, or we can describe a problem and ask them to 'design' a solution.
I found this interesting thing from the FAA in 1960 - scroll down to page 5. Maybe we could recreate this somehow.
Possible Question Starters:
**This is from the FAA. We would need to simplify it and clean it up.
The table below shows the impact force to the head during a a high speed crash. Impacts that would result in a concussion are to the left of the double line, and those that would be fatal to a human are to the right of the double line.
When engineers design the padding which surrounds people in the cabin of an airplane, they look for a thickness that will be sufficiently protective to humans, but they don't want something that will be too heavy. Based on this information, when designing the cabin of an airplane with a top speed of 35 ft/sec and a peak g-force of ?, padding with a thickness of which of the following will provide the maximum protection at the minimum weight?
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