physics - physical quantities, units and measurements

Physical Quantity

A physical quantity is a quantity that can be measured. It consists of a numerical magnitude and a unit.

Seven basic physical quantities

1. Length

2. Mass

3. Time

4. Electric current

5. Temperature

6. Amount of substance

Prefixes for SI units

Kilo, mega, giga, tera

Deci, centi, milli, micro, nano

Radius of earth

10^6 m

Diameter of earth

10^7 m

Size of an atom

10^-10 m

Precision

Precision is the smallest unit an instrument can measure

Parallax error

Due to incorrect positioning of eyes when taking readings

-allign line of sight perpendicularly to the markings

Zero error

The false reading that an instrument shows when the true value of the measured quantity is zero.

-tare the instrument

-measure from another point and subtract from final reading

Pendulum period

The period is the time taken to complete one entire oscillation

Improving accuracy

Repeat experiment multiple times and take mean of results

Scalar quantities

Scalar quantities are physical quantities that have magnitude only

-distance

-speed

-mass

-energy/work

-time

-power (w)

-pressure

Vector qualities

Vector quantities are physical quantities that have both magnitude and direction.

-displacement

-velocity

-acceleration

-force

-weight

Distance

Distance is the total length covered by an object regardless of the direction of motion.

Displacement

Displacement is the distance measured in a straight line in a specific direction.

Velocity

Is the rate of change of displacement

Digital calipers

Inside jaws- internal diameter

Outside jaws- external diameter

Tail- depth of an object

Locking Screw- ensure jaws do not move apart

Digital display- used to show numeric value

0.01mm

1. Close jaws gently

2. Tare

3. Place object between jaws and grip object

Digital micrometer screw gauge

Anvil and spindle- clamp on the object, measure its diameter

🌟Rachet and thimble- adjust the spindle so that the spindle is in contact with the object

0.001mm

2.5 cm max

Density

Mass/volume

Diameter of human hair n' wire

10^-4

10^-3