Measurement of Length and Motion · Lesson 4 of 5
Patterns and Types of Motion
“Classify motion by the path an object follows and explore linear, circular, oscillatory and periodic motion through everyday examples.”
• Identify linear, circular and oscillatory motion from the path of an object. • Explain the defining feature of each type of motion. • Use observations from simple investigations to classify motion. • Distinguish a circular path from a to-and-fro path. • Explain how repeated circular and oscillatory motions can be periodic.
The Path Tells Us About Motion
Once we know that an object is moving, we can ask a second question: what kind of path does it follow? A falling object may move approximately along a straight line, a point on a merry-go-round traces a circle, and a swing moves repeatedly to and fro. These different paths help us classify motion.
Linear Motion
When an object moves along a straight-line path, its motion is called linear motion. A dropped eraser, a fruit falling vertically, students marching along a straight path, or a box pushed straight across a floor can all illustrate linear motion.
Motion of an object along a straight-line path.
Problem
An eraser is released from rest and falls straight downward. What type of motion is this?
- 1.Observe the path followed by the eraser.
- 2.Its path is approximately a straight vertical line.
- 3.Motion along a straight line is linear motion.
- 4.Therefore, the falling eraser shows linear motion.
Circular Motion
A different pattern appears when an object moves around a fixed centre and follows a circular path. You can observe this by tying an eraser or potato to a thread and whirling it carefully. The moving object repeatedly traces a circle around your hand.
Motion of an object along a circular path.
Problem
A child sits on a moving merry-go-round. What type of path does the child follow around the centre?
- 1.The child moves around the central axis of the ride.
- 2.The path loops around the centre and is circular.
- 3.Therefore, the motion is circular motion.
Oscillatory Motion
A swing does not keep travelling around a circle or continue endlessly in one straight direction. Instead, it moves to one side, returns through a central region, moves to the other side and repeats. Motion of this kind is called oscillatory motion.
To-and-fro motion of an object about a fixed position.
You can investigate oscillation with a hanging eraser. Pull it slightly to one side and release it; the eraser moves repeatedly to and fro. A thin metal strip fixed at one end also oscillates if its free end is bent slightly and released.
Problem
A playground swing moves back and forth, and the free end of a bent metal strip moves up and down after release. What do these motions have in common?
- 1.Both move repeatedly on opposite sides of a fixed or central position.
- 2.Neither simply continues in one direction.
- 3.Both are examples of oscillatory motion.
When Motion Repeats
Some motions repeat the same path after equal intervals of time. Such repeated motion is called periodic motion. A steadily rotating object can repeat its circular path, and an oscillating object can repeat its to-and-fro path. For this reason, circular and oscillatory motions can be periodic when the repetition occurs regularly.
Motion that repeats its path after a fixed interval of time.
Circular motion and oscillatory motion are not the same. Circular motion follows a circular path around a centre, while oscillatory motion moves to and fro about a fixed position.
Classifying Motion in a Playground
A children's park contains several motion patterns at once. A child sliding down a straight slide can show linear motion, a merry-go-round shows circular motion, and a swing or seesaw shows oscillatory motion. The important skill is to justify the classification by describing the path.
| Object or situation | Type of motion | Reason |
|---|---|---|
| Child moving down a straight slide | Linear | Path is approximately straight |
| Merry-go-round | Circular | Moves around a centre |
| Swing | Oscillatory | Moves to and fro about a fixed position |
| Seesaw end | Oscillatory | Moves repeatedly up and down |
Quiz
What defines linear motion?
Which is the best example of circular motion?
Which statement best describes oscillatory motion?
What makes a motion periodic?
A thin metal strip fixed at one end moves repeatedly up and down after being released. What type of motion is it showing?
Practice Problems
- Give two everyday examples of linear motion and explain why each is linear.
- Give two everyday examples of circular motion and explain the path in each case.
- Give two everyday examples of oscillatory motion.
- Describe an investigation using a hanging eraser that demonstrates oscillatory motion.
- Explain how the motion of a merry-go-round differs from the motion of a swing.
- A ball moves through a track containing straight and looped sections. How would you classify its motion in each section?
- Find three moving objects in a playground and classify each as linear, circular or oscillatory with a reason.
Key Takeaways
• Linear motion follows a straight-line path. • Circular motion follows a circular path around a centre. • Oscillatory motion moves to and fro about a fixed position. • A motion is periodic when it repeats after a fixed interval of time. • Classify motion by observing and explaining the path followed by the object.