CH 1: Physical Quantities, Units and Measurements

• A physical quantity is a unit that can be measured, consisting of magnitude and a unit.
• The modern length of a flat pole is 5.5 meters, which is the magnitude of a physical quantity and meters (m) is the unit.
• SI unit is a standardized unit used worldwide.
• There are two types of physical quantities: base quantities and derived quantities.
• Base quantities are quantities that cannot be derived from other quantities and can only be measured.
• The seven base quantities are length, time, mass, temperature, electric current, amount of substance, and luminous intensity.
• Derived quantities are quantities that are derived from base quantities, and their corresponding units are called derived units.
• Any other quantities not in the seven base quantities are derived quantities.
• Examples of derived quantities include distance divided by time (m/s), volume (m³), and acceleration (m/s²).
• To read the scale of vernier calipers, align the marking on the main scale with the marking on the vernier scale.
• The locking screw of vernier calipers is used to tighten the moving part of the instrument.
• If there is a zero error of negative 0.04 cm, the corrected reading is the measured reading plus 0.04 cm.
• If there is no zero error, the character reading is the measured reading.
• The depth measuring blade of vernier calipers can be used to measure the depth of an object.
• Zero error occurs when measurement does not start from zero, resulting in a reading shown when it should be zero.
• The main scale of vernier calipers is in centimeters (cm), while the vernier scale is in millimeters (mm).
• Vernier calipers have an internal jaw (internet jaws) and an external jaw (external jaws), which can be used to measure internal diameter or internal length of an object and external diameter or external length of an object respectively.
• The diameter of a ball bearing can be measured using vernier calipers, with no zero error, zero error of positive 0.04 cm, and zero error of negative 0.04 cm.
• The period of a simple pendulum is independent of the angle of oscillation θ.
• The mass of the bob m and the length of the pendulum l are parameters that affect the period of a simple pendulum.
• The period of a pendulum is calculated using the formula T = 2π square root of l/g.
• The time taken for a pendulum to swing 20 complete oscillations is 8 seconds.
• The sleeve has the main scale in mm and the scale in the timber is in 0.01 mm divisions.
• A spindle and the non-moving part is the end wheel, which moves when the timber is turned.
• To measure time, use an analog or digital stopwatch.
• The ratchet is used to make sure that the object being measured is not pushed too hard by the spindle.
• If there is a positive zero error, the zero mark on the main scale is same and the marking on the timber scale coincides with the bottom line, meaning the correct reading will be the measured reading minus zero error.
• The period of a simple pendulum can be found by timing 20 complete oscillations and dividing the average time by 20.
• If there is a negative zero error, the zero mark of the main scale is covered by the timber and the marking on the timber scale coincides with the datum line, meaning the correct reading will be the measured reading minus zero error.
• If there is no zero error, the zero mark on the main scale is at the edge of the timber and the zero mark on the timber scale coincides with the datum line, meaning the correct reading will be the same as the measured reading.
• To check for zero error, close the micrometer screw clutch completely and look at the scale.
• To use a micrometer screw clutch, close the jaws of the micrometer, place the wire or metal ball between the end wheel and the spindle end, rotate the timber until it touches the wire or the metal ball, and then rotate the ratchet until a click sound is heard.
• To read from the scale, check from the main scale in mm, and then check which marking on the timber scale corresponds to the marking on the main scale.
• The minimum resultant vector is obtained when the two vector quantities are in the opposite direction.
• Systematic error in measurement is caused by factors that reduce the accuracy, such as zero error.
• The range of a measuring instrument is the maximum length that it can measure.
• The starting point is point 'a' where the student runs 300 meters towards the north, resulting in a length of 3 cm.
• The common measuring instruments used in physics lab are meter rule, measuring tape, vernier calipers, and micrometer screwcard>
• Accuracy in measurement is the extent to which a reading of a measurement is close to the actual value.
• The correct positioning of the eye in measurement is when the observer's eye is vertically above the markings.