Physics Study Guide • Chapter 5 Quick Review
In ancient times, people used inconsistent body parts to measure:
The Problem:
Body dimensions vary per person! This created massive confusion, necessitating a universal standard.
The worldwide standard system is the International System of Units (SI Units).
SI Unit of Length = Metre (m)
Placement:
Place the scale parallel and in complete contact with the object along its entire length.
Eye Alignment:
Your eye position must be directly vertically above the target point. Looking from angles causes parallax error!
Eye (A) ← WRONG | Eye (B) ↓ CORRECT | Eye (C) → WRONG
Broken Scales:
If the zero end is worn/broken, measure from another mark (e.g., 1.0 cm):
True Length = End Value − Start Value
Example: 10.4 cm − 1.0 cm = 9.4 cm
Measuring Curved Lines:
You cannot use a straight wooden ruler directly!
The Thread Trick:
What is a Reference Point?
A fixed, stationary location used to state the position or observe the motion of an object.
Example: A bus stand, milestone, or gate post from which distances are measured.
Motion:
An object is said to be in motion if its position changes with respect to a fixed reference point over time.
Rest:
An object is said to be at rest if its position remains unchanged relative to a fixed reference point over time.
Relative Nature of Motion:
A passenger inside a moving bus is at rest relative to other passengers inside, but in motion relative to trees outside!
Linear Motion
Movement along a perfectly straight line path.
e.g., Falling apple, marching troops, sliding box
Circular Motion
Movement of an object along a circular trajectory path.
e.g., Hands of a clock, merry-go-round, spinning top
Oscillatory Motion
Continuous to-and-fro movement about a fixed, stable position.
e.g., Simple pendulum, swing, vibrating ruler
Periodic Motion
Any motion that repeats its path after exact, fixed intervals of time.
Note: Circular & Oscillatory motions are often periodic.