MEASUREMENT OF MASS, WEIGHT, LENGTH & TIME

TECHNIQUES AND MEASUREMENT

Measurement is an important aspect of physics or other sciences. No fact in science is accepted, no law is established, unless it can be exactly measured and quantified. As physics is based on exact measurements, every such measurement requires two things; first a number or quantity, secondly a unit, e.g. 20 metres as the length of a table tennis’s board.

MEASUREMENT OF LENGTH

THE METRE RULE: The metre rule is often used to measure distances of a few centimetres to some metres, for example, the dimensions of a table or room. When longer distances are involved, tape rule can be used. 0.1 cm or 1mm is the smallest graduation on a metre rule.

CALLIPERS:

Callipers are used to measure distances on solid objects where an ordinary metre rule cannot be applied directly. They are made of hinged steel jaws which are closed (in the case of external callipers) until they touch the desired part of the object being measured. The distance between the jaws is then measured on a graduated scale such as the metre rule.

THE VERNIER CALLIPERS

These can measure length more accurately than the metre rule. To measure small lengths, to the nearest 0.1mm, e.g the thickness of a metre rule, the internal and external diameters of a tube, or the diameter of a rod, we use the vernier callipers. The instrument has two sets of jaws and two scales, the main and the vernier scales

THE MICROMETER SCREW GAUGE

This instrument measures even smaller lengths (e.g diameter of a wire) than the vernier callipers. It has a higher reading accuracy and can read up to 0.01mm or 0.001cm. It can be used to measure the thickness of a piece of paper, the diameter of a small ball (e.g. pendulum bob).

MEASUREMENT OF TIME

The time internal between two events is the difference between the times when the event occurred when the time internal is of the order of minutes or hours, clocks and watches can be used. These are the instruments which indicate the time of the day. For shorter time intervals of the order of seconds, stop clocks or stop watches are used.

EVALUATION

Define (a) length (b) time.
List five instrument for measuring length.

MEASUREMENT OF MASS

The mass of a body is a measure of the quantity of matter it contains. Mass is usually measured by comparing it with standard masses, using a balance.

There are various types e.g. beam or chemical balance, lever balance, a dial spring, direct reading balance etc

WEIGHT: of a body is the force acting on the body due to the earth’s gravitational pull. One instrument used for measuring weight is the spring balance. Weight is measured in Newtons.

Differences between Mass and Weight

	Mass	Weight
1.	Mass is the quantity of matter present in a body.	Weight occurs due to the force of gravity acting upon an object.
2.	Mass is constant.	Weight varies.
3.	Mass is a scalar quantity.	Weight is a vector quantity.
4.	The unit of mass is the kg.	The unit of weight is the Newton (N).
5.	Mass is measured by chemical or beam balance.	Weight is measured by spring balance.
6.	The principles of moment is applied to obtain the mass.	The instruments for measuring weight obeys Hook’s law.

Relationship Between mass & weight

W=mg

Where, W = weight(N) m=mass(kg) g= acceleration due to gravity(m/s²)

MEASUREMENT OF VOLUME

GRADUATED CYLINDER: A graduated cylinder can be used for measurement of volumes of liquids. It is accurate to the nearest 1cm³. It can also be used in measuring the volume of irregular shaped objects e.g stone, with the aid of the displacement or eureka can.

HOW TO READ A VERNIER CALLIPER

In reading a vernier calliper, the whole number (digit before the decimal point) and the first digit after the decimal point are read from the main scale while the second digit after the decimal point is read from the vernier scale (sliding scale). This is the point or mark that coincides with that of the main scale.

Example 3.2 (How to read the micrometer scale)

What is the reading on the micrometer screw gauge shown below?

EVALUATION

Differentiate between mass & weight
The weight of an object of mass 5000g is ……. (take g = 10m/s²)

WEEKEND ASSIGNMENT

Which of the following instrument is suitable for taking the most accurate measurement of the internal diameter of a test-tube? (a) Metre rule (b) A pair of callipers (c) A micrometer screw gauge (d) A tape rule
Which of the following statements about mass and weight of a body is not correct? Its (a) mass is a scalar quantity (b) weight is a function of the gravitational pull on it (c) mass on earth and on the moon is the same (d) weight at the equator and at the poles is the same
The diagram below represents a portion of a micrometer screw guage. What is the reading? (a) 3.72mm (b) 3.50mm (c) 3.30mm (d) 3.25mm
The weight of a body is measured with

(a) spring balance (b) beam balance (c) chemical balance (d) lever balance

Which instrument is best for measuring small quantity of liquid?

(a) Burette (b) Pipette (c) Cylinder (d) Beaker

What is the dimension of force? (a) MLT⁻² (b) ML²T (c) ML2T⁻² (d) MLT⁻³
The diagram below represents a portion of a vernier calliper. What is its reading?

(a) 4.36cm (b) 4.43cm (c) 5.53cm (d) 5.44cm

Which of the following instruments is the best for measuring the diameter of the constantan wire? (a) Callipers (b) Mere rule (c) Micrometer screw guage (d) watt meter
Hydrometer is an instrument used for measuring

(a) relative humidity (b) dew point (c) relative density (d) attitude

What is the reading on the instrument? (a) 5.25mm (b) 10.16mm (C) 10.15mm

(d) 5.10mm

THEORY

Mention the instrument that is suitable to measure the following quantities;

(a) The weight of a body (b) The internal diametre of a test tube

(e) The length of a table (f) The diameter of a wire