published by
the Public Broadcasting Service
technical implementer:
the Show of Force Productions

This video-based resource examines centripetal force through the motion of circus animals running around a ring. Objects moving in a circle (even at constant speed) are experiencing acceleration because the center-seeking force causes a change in velocity. The video can serve to help students understand that an unbalanced force can change the direction of the velocity vector but not its magnitude. It includes tips on how to incorporate the video into instruction, discussion questions, and accompanying classroom activities.

This resource was developed in conjunction with the PBS series Circus. See Related Materials for a link to the full set of 8 Circus Physics video-based lessons.

6-8: 4F/M3b. If a force acts towards a single center, the object's path may curve into an orbit around the center.

9-12: 4F/H1. The change in motion (direction or speed) of an object is proportional to the applied force and inversely proportional to the mass.

9-12: 4F/H4. Whenever one thing exerts a force on another, an equal amount of force is exerted back on it.

9-12: 4F/H8. Any object maintains a constant speed and direction of motion unless an unbalanced outside force acts on it.

11. Common Themes

11C. Constancy and Change

9-12: 11C/H4. Graphs and equations are useful (and often equivalent) ways for depicting and analyzing patterns of change.

Next Generation Science Standards

Motion and Stability: Forces and Interactions (HS-PS2)

Students who demonstrate understanding can: (9-12)

Analyze data to support the claim that Newton's second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration. (HS-PS2-1)

Disciplinary Core Ideas (K-12)

Forces and Motion (PS2.A)

The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion. (6-8)

Newton's second law accurately predicts changes in the motion of macroscopic objects. (9-12)

Relationship Between Energy and Forces (PS3.C)

When two objects interact, each one exerts a force on the other that can cause energy to be transferred to or from the object. (6-8)

NGSS Science and Engineering Practices (K-12)

Using Mathematics and Computational Thinking (5-12)

Mathematical and computational thinking at the 9â12 level builds on Kâ8 and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions. (9-12)

Use mathematical representations of phenomena or design solutions to support and revise explanations. (9-12)

Common Core State Standards for Mathematics Alignments

High School â Algebra (9-12)

Seeing Structure in Expressions (9-12)

A-SSE.1.a Interpret parts of an expression, such as terms, factors, and coefficients.

High School â Geometry (9-12)

Circles (9-12)

G-C.2 Identify and describe relationships among inscribed angles, radii, and chords.

<a href="http://www.thephysicsfront.org/items/detail.cfm?ID=13043">Show of Force Productions. Circus Physics: Centripetal Acceleration. Arlington: Public Broadcasting Service, 2010.</a>

Circus Physics: Centripetal Acceleration. (2010). Retrieved January 20, 2017, from Public Broadcasting Service: http://www.pbslearningmedia.org/resource/6b92cb91-72bb-4d87-a8ea-8171506bde35/6b92cb91-72bb-4d87-a8ea-8171506bde35/

Show of Force Productions. Circus Physics: Centripetal Acceleration. Arlington: Public Broadcasting Service, 2010. http://www.pbslearningmedia.org/resource/6b92cb91-72bb-4d87-a8ea-8171506bde35/6b92cb91-72bb-4d87-a8ea-8171506bde35/ (accessed 20 January 2017).

Circus Physics: Centripetal Acceleration. Arlington: Public Broadcasting Service, 2010. Show of Force Productions. 20 Jan. 2017 <http://www.pbslearningmedia.org/resource/6b92cb91-72bb-4d87-a8ea-8171506bde35/6b92cb91-72bb-4d87-a8ea-8171506bde35/>.

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