Course:
Physics - 0571
Length and time are fundamental physical quantities used in physics to describe the size of objects and the duration of events. These quantities are measured using standard international units known as SI units.
Length is measured in metres (m) and time is measured in seconds (s). Accurate measurement is important in scientific experiments, and different instruments are used depending on the size of the object being measured.
For example, rulers measure larger objects, while Vernier calipers and micrometer screw gauges measure smaller lengths with higher precision. Time is commonly measured using stop clocks or stop watches.
Measurements may contain errors caused by faulty instruments, incorrect reading or human reaction time. Scientists therefore estimate the accuracy of instruments and repeat measurements to reduce errors.
One practical experiment used to study time measurement is the simple pendulum experiment, which helps determine the period of oscillation.
Physical quantities are properties of a system that can be measured.
Length and time are two of the most commonly measured quantities in physics.
Different instruments are used to measure length depending on the required precision.
A ruler is used to measure larger lengths such as:
• the length of a book
• the height of a table
• the length of a laboratory bench
Typical accuracy: ±1 mm
Example in school experiment:
Students may measure the length of a wooden rod using a metre rule.
A Vernier caliper measures smaller lengths more accurately than a ruler.
It is used to measure:
• diameter of a pipe
• thickness of a coin
• internal diameter of a tube
Typical accuracy: ±0.1 mm
A micrometer screw gauge measures very small thicknesses.
It is used to measure:
• thickness of a sheet of paper
• diameter of a thin wire
• thickness of a metal plate
Typical accuracy: ±0.01 mm
Errors may occur during measurement due to:
This happens when the scale is viewed at an angle instead of directly above it.
Example:
When reading a ruler from the side rather than from above.
Occurs when the instrument does not read zero when nothing is being measured.
Example:
A Vernier caliper showing 0.02 mm when closed.
Old rulers may have faded markings or damaged edges.
Time is measured using instruments such as:
• stop clock
• stop watch
• digital timer
These instruments measure the duration of events.
• measuring the time taken for a ball to roll down a ramp
• measuring the period of a pendulum
Typical reaction time of humans is about 0.2 seconds, which can cause small errors.
Errors may occur due to:
Delay when starting or stopping the stopwatch.
Instrument may run too fast or too slow.
When counting repeated movements such as pendulum swings.
Accuracy refers to how close a measured value is to the true value.
The accuracy of an instrument depends on its smallest scale division.
The smaller the scale division, the more accurate the instrument.
A pendulum consists of a mass attached to a string that swings back and forth.
The period (T) is the time taken for one complete oscillation.
• string
• small metal mass
• stand
• stopwatch
Attach the mass to the string.
Fix the string to a stand.
Pull the mass slightly to one side and release it.
Measure the time taken for 10 oscillations.
Calculate the period.
To improve accuracy:
• measure time for many oscillations instead of one
• repeat the experiment several times
• take the average value
Accurate measurement is important because it:
• ensures reliable experimental results
• allows scientists to compare data
• helps identify physical laws
Measurement skills are essential in physics, engineering, medicine and technology.
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