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2.1 Picturing Motion

● Draw motion diagrams to describe motion.

● Develop a particle model to represent a moving object.

In this section you will:

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2.1 Picturing Motion

Perceiving motion is instinctive—your eyes pay more attention to moving objects than to stationary ones. Movement is all around you.

Movement travels in many directions, such as the straight-line path of a bowling ball in a lane’s gutter, the curved path of a tether ball, the spiral of a falling kite, and the swirls of water circling a drain.

All Kinds of Motion

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2.1 Picturing Motion

When an object is in motion, its position changes. Its position can change along the path of a straight line, a circle, an arc, or a back-and-forth vibration.

All Kinds of Motion

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2.1 Picturing Motion

A description of motion relates to place and time. You must be able to answer the questions of where and when an object is positioned to describe its motion.

Movement Along a Straight Line

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2.1 Picturing Motion

In the figure below, the car has moved from point A to point B in a specific time period.

Movement Along a Straight Line

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2.1 Picturing Motion

Motion Diagrams

Click image to view movie.

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2.1 Section Check

Explain how applying the particle model produces a simplified version of a motion diagram?

Question 1

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2.1 Section Check

Answer 1

Answer: Keeping track of the motion of the runner is easier if we disregard the movements of the arms and the legs, and instead concentrate on a single point at the center of the body. In effect, we can disregard the fact that the runner has some size and imagine that the runner is a very small object located precisely at that central point. A particle model is a simplified version of a motion diagram in which the object in motion is replaced by a series of single points.

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2.1 Section Check

Which statement describes best the motion diagram of an object in motion?

Question 2

A. a graph of the time data on a horizontal axis and the position on a vertical axis

B. a series of images showing the positions of a moving object at equal time intervals

C. a diagram in which the object in motion is replaced by a series of single points

D. a diagram that tells us the location of the zero point of the object in motion and the direction in which the object is moving

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2.1 Section Check

Reason: A series of images showing the positions of a moving object at equal time intervals is called a motion diagram.

Answer 2

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2.1 Section Check

What is the purpose of drawing a motion diagram or a particle model?

Question 3

A. to calculate the speed of the object in motion

B. to calculate the distance covered by the object in a particular time

C. to check whether an object is in motion

D. to calculate the instantaneous velocity of the object in motion

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2.1 Section Check

Reason: In a motion diagram or a particle model, we relate the motion of the object with the background, which indicates that relative to the background, only the object is in motion.

Answer 3

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2.2 Where and When?