Module 2 - Foundations of Physics

What is a physical quantity?

Something that you can measure.

What is homogeneity of units?

The units in any equation must always be equivalent (in terms of S.I. base units) on both sides.

Name 5 physical quantities and base units

Amount of substance (mole) x Temperature (kelvin) x Length (metre) x Time (second) x Mass (kilogram) x Current (ampere)

What axis does the independent variable go on?

x-axis

What axis does the dependent variable go on?

y-axis

Definition of error

The difference between the measured value and true value of measurement.

Definition of systematic error

An error that causes the measurements to differ from the true value by the same amount.

Sources of systematic error

Imperfect calibration

Imperfect methods of observation

Interference of environment with method process

How to reduce systematic errors

Repeating experiment using a comparable apparatus to identify the source of error

Accurate calibration of equipment

Confirming experimental method against literature and sources

Definition of random error

An error caused by unpredictable circumstances and resulting in measurements that differ from the true value by varying amounts.

Sources of random error

Mistakes made in inaccurate readings made by the experimenter.

Fluctuations in the reading on the instrument.

How to reduce random errors

Taking averages over multiple measurements, not including anomalous results.

Repeating the experiment and averaging across all the measurements.

Definition of uncertainty

The degree to which we can say a measurement is accurate.

A measurement of 15.5 cm on a ruler would have an absolute uncertainty of + or - 0.1 cm.

Definition of accuracy

A measurement is accurate if its value is in close proximity to the accepted true value.

Definition of precision

A measurement is precise if its value is in close proximity to the other repeated measurements of the same quantity.

Give an example of a random error.

If you measured the length of a wire 20 times, the chances are you'd get a slightly different value each time.

A ball bearing is released into a tall cylinder of clear oil. The ball bearing initially accelerates but soon reaches terminal velocity. By considering the forces acting on the ball bearing, explain its motion.

Initially, weight > drag so resultant force is downwards & object accelerates. This increase in velocity increases the drag force until it balances the weight. No resultant force so no acceleration so constant terminal velocity.

How would you demonstrate that the ball bearing had reached terminal velocity?

Time how long it takes the ball bearing to travel a set distance measured using a ruler. Work out speed = distance/time & check that it remains constant.