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Home Concept Builders 1D Kinematics Motion Diagrams Help Help 2

Motion Diagrams - Questions 2 Help

Force diagrams like the one shown depict the direction and strength of forces by vector arrows. Longer arrows mean stronger forces. One can determine if the forces are balanced by looking at the arrow size. Equal length arrows in opposite directions mean that the forces are balanced. Such situations are consistent with constant speed. Unequal-length arrows in opposite directions mean the forces are unbalanced and the object will accelerate.

In Activity 1 and Activity 2, you will have to construct a motion diagram for six different verbal descriptions. The second question involves the following verbal description.
 

Question 2:

A bicycle is moving with a constant, leftward velocity.

Dot Spacing

This verbal description is of a constant velocity (or constant speed) motion. An object that moves at a constant speed covers the same distance each second. One would expect the distance between adjacent dots to be constant.
 

Velocity Vectors

There are two important questions to answer when selecting the set of velocity vectors. First, which direction do the vectors point? And second, is the length staying constant, increasing, or decreasing? The first question is easiest to answer. Velocity can be thought of as speed with a direction. The direction of the velocity is simply the direction that the object is moving. The second question pertains to the length of the vector arrow and that is where the speed comes in. A constant speed motion will be represented by velocity vectors with constant length.
 

Acceleration Vectors

The first question to ask is: Is the object accelerating? Accelerating objects are either changing their speed or their direction. None of the objects in this Concept Builder are changing direction. But there are some speed changes among the six descriptions. If the speed is constant, then the acceleration is zero and there is only one choice of vectors that fits this description. Select it and you'll be successful.

The following pages from The Physics Classroom Tutorial provide additional information related to this topic:

Velocity versus Speed

Acceleration

Dot Diagrams (or Ticker Tape Diagrams)

Vector Diagrams

Concept Builder Teacher Notes Directions