Learning to Think About Gravity

Misconceptions

Claudine Kavanagh Esther Zirbel

Tufts University

Thinking about gravity

1. History and Gravity as a Force

2. “Misconceptions”3. Effective instruction

History of gravity

Aristotle: 4 elements, 2 domains. Gravity is not a force.

Newton: Gravity = force across entire universe.

Einstein: Space tells matter how to move. Matter tells space how to curve. Gravity is not a force.

2) “Misconceptions”

Is there gravity in space? (Think/pair/share)

Equivalence PrincipleWhy are these people weightless?(Think/pair/share)

Learning gravity? Easy! Right?!

Viennot (1979): University of ParisTested undergraduates’ conceptual understanding of projectile motion

Most students drew arrows in the direction(s) of motion

Students’ ideas were identical to pre-Newtonian “impetus” taught at the same university 600 years earlier by John Buridan

Misconceptions: Free Fall

1) Things fall if not supported 2) Strength and effort prevent

falling3) Gravity is not a force4) Heavier objects fall faster5) Gravity acts only on heavy,

slow, inactive objects6) Gravity acts upwards on a

falling object

Misconceptions: Projectile Motion1) Motion implies a force in the

direction of motion2) Objects fall straight down if not

supported (inverted L)3) Impetus may wear out/ be overcome4) Living or active things impart

impetus5) Projectiles continue to

accelerate after release

Misconceptions: OrbitsGravity needs airThere is no gravity in spaceObjects in orbit are weightless, so gravity does not affect them

The force of gravity diminishes with increasing altitude

Force is needed to keep an object in orbitPlanets closer to the sun (or with fast spin) have more gravity

Gravitational attraction between objects is not equal and opposite

Misconceptions Summary

Few graduates-including those with top grades- understand the foundational concept of gravity.

What does everyday experience contribute to students’ understanding of gravity?

Chapter 3: Effective instruction

What are students expected to learn? National Science Education Standards K-5: Magnetism (action-at-a-distance).

6-8: Falling motion, projectile motion and orbits. Gravity is “a ubiquitous force that holds the universe together”

9-12: Newton’s laws & calculations of gravitational force. Three theoretical issues:

Universal gravitation Massive structures in the Universe General relativity (historical only)

Teaching: What works? Hynd, Alvermann & Qian (1997) studied 73 pre-service teachers learning about gravity & projectile motion

All participants “non-Newtonian” on pre-test Different intervention methods: what worked?

Only 2 participants converted to Newtonian explanation

Same 2 had been predisposed to scientific “frame of mind”!

“personal motivation” “tendency to view scientific information as useful”

Teaching: What works?

Prescott: two “intervention” teachers & two “control” teachers.

Intervention taught gravity qualitatively first, then quantitatively

“The most significant factor determining whether student misconceptions were eliminated was found to be the teachers’ ability to deal with their own misconceptions” (Prescott, 2004)

Teaching: What works?

How would you answer this question?(Think/pair/share)Smith & Peacock (1992) identified two apparent contradictions in teaching gravity: 1. “Heavier things” experience greater attraction, yet accelerate at the same rate as “lighter things”

2. “Light objects” fall at a constant rate

More research?

No data found: Elliptical orbits Universal applicability of same physical laws

Large scale structure seen in the U today

Einstein’s general theory of relativity

Equivalence principle

Anti-gravity research here at Tufts?

Thank you!Q&A?