A2L Item 058

Goal: Perceiving acceleration from description of motion.

Source: UMPERG Core A.4

How many of the objects below are NOT accelerating?
(A) A race car going around a circular track at 150 MPH
(B) A sky diver falling at a constant speed
(C) A heavy box sliding across the floor, after being released
(D) A bowling ball colliding with a pin
(E) A vibrating guitar string
(F) A baseball flying through the air
(G) A child swinging on a swing

1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7

Commentary:

(1) Only the skydiver, who has reached terminal velocity, has zero
acceleration. In each of the other situations either the speed or
direction of motion is changing.

Background

Students may use a variety of factors in deciding whether an object
accelerates.

The goal is to focus students more narrowly on changes in the speed
and/or direction of an object’s motion.

Questions to Reveal Student Reasoning

How do you know whether an object is accelerating? What are some
examples of objects undergoing an acceleration?

Suggestions

Play a “challenge game” with the class where two teams of students take
turns challenging each other with situations in which an object
undergoes some motion, and the other team needs to determine whether or
not the object is accelerating.

Have students write out how they determine whether an object is
accelerating. After listening to the different method students use,
have students vote on which method they think is best.

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