Free Fall Lesson

Content Area: Physics (11-12)
Topic: Kinematics
Sub-Topic: Free Fall

Computer requirements: Vensim, STELLATM, Interactive Physics or Excel

Prior content covered: Linear velocity and acceleration

Estimated time for computer portion of lesson: 45 min

Essential Questions or Ideas to address:

• What does free fall look like in various worlds?
• How does free fall affect the motion of objects that are thrown upward or downward compared to those that are just dropped?

The lesson (90-min block): After investigating free fall in the laboratory, students can build or use a Vensim/STELLA model, Excel spreadsheet or an Interactive Physics simulation to further investigate free fall.  In one activity, they use the model to compare free fall on earth, the moon, and another planet. In a second activity, they compare the motion of three objects on earth: one is dropped, one is thrown downward and one is thrown upward.  For an example of a model and companion activities see the Free Fall Activity Packet.

• When an object is thrown upward, at the top of the flight path, the acceleration is zero.
• Objects thrown upward and downward retain some "extra" acceleration that is observable in the velocity-time graph.

Evaluation of lesson effectiveness: Students find the first activity interesting for its novelty.  This is easier to do in STELLA or Excel where comparative graphs can be maintained while the acceleration is changed. The second activity can be accomplished in any of the modeling environments. The position-time and velocity-time graphs for these three motions provide rich opportunities to assess student understanding of graphs of these variables and the meaning of slope and y-intercept, especially on the velocity - time graph.

Alternate presentation:  There are many applets available on the web.

Math topics: Linear and quadratic equations, graph interpretation for those equations

Extensions:  The falling filters and parachute models presented under the sub-topic of drag are natural extensions of this model.

Standards:

MSDE (from the website as of 9/05):

 Physics/Core Learning Goals Science Indicator 5.1.2 The student will use algebraic and geometric concepts to describe an object's motion. Assessment Limits direction, position, distance/displacement, speed/velocity, motion with a constant acceleration, one and two dimensional motion, frames of reference Goal 5 Concepts Of Physics The student will demonstrate the ability to use scientific skills and processes (Core Learning Goal 1) to explain and predict the outcome of certain interactions which occur between matter and energy. Expectation 5.1 The student will know and apply the laws of mechanics to explain the behavior of the physical world.

The standards do not directly address kinematics, but an understanding of motion is necessary before students can address the standards as they appear here.

National Science Standards:

Physical Science: Motion and Forces:
Objects change their motion only when a net force is applied. Laws of motion are used to calculate precisely the effects of forces on the motion of objects. The magnitude of the change in motion can be calculated using the relationship F = ma, which is independent of the nature of the force.  Whenever one object exerts a force on another, a force equal in magnitude and opposite in direction is exerted on the first object.

AAAS Benchmarks:

The Physical Setting: Forces of Nature:

• The change in motion of an object is is proportional to the applied force and inversely proportional to the mass.
• All motion is relative to whatever frame of reference is chosen, for there is no motionless frame from which to judge all motion.

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