2.1 Foundations of Physics

Physical quantity

a quantity that can be measured, that has both a **numerical value** and a **unit**

Homogeneity of units

the S.I. base units must always be equivalent on both sides in any equation

Precise results

the smaller the amount of spread of your data from the mean

Repeatable results

you can repeat an experiment multiple times and get the same results

Reproducible results

someone else can recreate your experiment using different equipment or methods, and get the same results you do

Valid results

precise and answers the original question

Accurate results

really close to the true answer

What does random error affect?

precision

Random error

the unpredictable vary of a quantity

Causes: Random error

* vibrations and air convection currents
* temperature variations
* misreadings
* variations across measurements
* not enough data
* instrument sensitivity
* parallax error

Solutions: Random error

* repeats
* calculating the mean average

What does systematic error affect?

accuracy

Systematic error

a consistent, repeatable error due to the equipment, method or technique

Causes: Systematic error

* bad instruments
* poor calibration
* zero error
* poorly timed actions
* parallax error
* environment
* experimental method

Solutions: Systematic error

* repeat with a different technique or apparatus
* calibrate the apparatus (by measuring a known value)

Zero error

a systematic error when a measuring instrument falsely reads a non-zero value when the true value being measured is zero

Solution: Zero error

calibrate the apparatus

Validity

required data is obtained by an acceptable method that reaches a conclusion that reflects reality

Resolution

the smallest change in what’s being measured that can be detected by the equipment

Anomalous result

a result that doesn’t fit in with the pattern of the other results in a set of data

When should you ignore an anomalous result?

* calculating averages
* drawing a line of best fit

Equation: Percentage uncertainty

percentage uncertainty = (absolute uncertainty/measurement) x 100

Equation: Adding or subtracting uncertainties

**add** the **absolute uncertainties**

Equation: Multiplying or dividing uncertainties

**add** the **percentage uncertainties**

Equation: Raising uncertainties to a power

**multiply** the **percentage uncertainty** by the **power**

Equation: Percentage difference

percentage difference = ((experimental value - accepted value)/accepted value) x 100

Independent variable

the variable you change in an experiment

What axis is the independent variable on?

x-axis

Dependent variable

the variable you measure in an experiment

What axis is the dependent variable on?

y-axis

Control variable

a variable that is kept constant in an experiment

Uncertainty in gradient

the difference between the best gradient and the worst gradient

How is no uncertainty represented graphically?

when the best and the worst gradient lines pass through the origin

Scalar

a quantity with magnitude (no direction)

Vector

a quantity with magnitude and direction

Equation: Horizontal component (Fx)

Fx = F**cos**θ

Equation: Vertical component (Fy)

Fy = F**sin**θ