1.1.1Motion, Forces and Energy
Measurement — Cambridge IGCSE Co-ordinated Sciences 0654 - Physics Revision Notes & Topical Questions
5 min read 9 parts Lesson 2 of 36
Part 1 of 7Measuring length
Ruler
- Ruler it measures small distances of a few centimetres to the nearest millimetre, in cm or mm
Tape measure
- Tape measure it measures lengths of tens of centimetres and more
Reading a scale
- Reading a scale look straight at the mark to avoid parallax error
Extended instruments
- Extended instruments vernier calipers read to 0.1 mm and a micrometer screw gauge reads to 0.01 mm
- They suit small objects such as the diameter of a wire.
Part 2 of 7Measuring volume
Measuring cylinder
- Measuring cylinder it measures the volume of a liquid in cm³ (1 cm³ = 1 mL)
Reading
- Reading read the bottom of the meniscus with the eye level with the liquid
Irregular solid
- Irregular solid put it in water and find the change in volume reading
Regular solid
- Regular solid calculate the volume from its dimensions, for example length × width × height for a cuboid
Part 3 of 7Measuring time
Clocks
- Clocks they usually measure long time intervals
Digital timers
- Digital timers stopwatches measure short time intervals
Reaction time
- Reaction time an alert person has a human reaction time of about 0.2 to 0.3 s
Effect
- Effect reaction time matters most when the time measured is very short
Part 4 of 7Multiple readings
Purpose
- Purpose taking multiple readings reduces the effect of measurement errors and improves precision
Small measurements
- Small measurements if the measurement is small, the percentage uncertainty is large
Thin objects
- Thin objects measure many identical items and divide
- The thickness of 100 sheets of paper divided by 100 gives the thickness of one sheet.
- The total length of four ball bearings divided by four gives the diameter of one.
Oscillations
- Oscillations time many swings and divide
- Timing 10 oscillations and dividing by 10 reduces the reaction-time error for the time of one oscillation.
Reference marker
Reference marker a line or dot at the equilibrium position that makes it easier to see when the pendulum passes,
- reducing the starting and stopping error
Part 5 of 7Time interval from a stopwatch
1
Read the start and finish times from the stopwatch display in minutes, seconds and hundredths.
2
Convert both readings to seconds.
3
Subtract the start time from the finish time.
4
Give the answer in seconds.
Part 6 of 7Prefixes and units
SI units
- SI units the metre for length, the kilogram for mass, the second for time and the kelvin for temperature
Large prefixes
- Large prefixes kilo (k) = 10³, mega (M) = 10⁶, giga (G) = 10⁹
Small prefixes
- Small prefixes centi (c) = 10⁻², milli (m) = 10⁻³, micro (µ) = 10⁻⁶, nano (n) = 10⁻⁹
Conversion
- 2.5 km = 2500 m and 340 ms = 0.34 s
Part 7 of 7More from the specification
More from the specification
Scalars and vectors
- Scalars and vectors scalars have only magnitude, vectors have magnitude and direction.
Vector examples
- Vector examples displacement, velocity, force and acceleration are vectors; mass, speed and time are scalars.
Resultant
- Resultant the single vector with the same effect as several, found by scale drawing or Pythagoras.
Measurement quantity
- Measurement quantity every quantity is a numerical value with a unit, and readings should be taken carefully.
Force vectors
- Force vectors force direction matters, so forces in opposite directions subtract.
Vector diagram
- Arrow diagram of vectors.
Vector
- Quantity with magnitude and direction.
Scalar
- Quantity with magnitude only.
Resultant
- Vector sum of two or more vectors.
Force
- A push or pull measured in newtons.
Displacement
- Change in position.
Velocity
- Rate of change of displacement.
Component
- Part of a vector along one axis.
Resultant vector
- Single vector equivalent to a combination of vectors.
Key terms
| Term | Meaning |
|---|---|
| Meniscus | Curved surface of a liquid in a measuring cylinder. |
| Reaction time | Delay of about 0.2 to 0.3 s in starting and stopping a timer by hand. |
| Oscillation | One complete swing of a pendulum. |
| Parallax error | Error from reading a scale from the wrong angle. |
| Reference marker | Mark at the equilibrium position of an oscillation. |
| SI unit | Standard internationally agreed unit. |
Avoid these mistakes
1
Measuring one thin sheet or one swing directly — measure many and divide.
2
Reading a scale at an angle — parallax error makes the reading wrong.
3
Reading the top of the meniscus — read the bottom of the curve.
4
Forgetting the unit or not converting it — write the unit and convert to SI before substituting.
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