Module 2: Chapter 2 - Foundations of Physics Flashcards
What is a physical quantity?
A measurement which has a numerical magnitude and an appropriate unit
What are SI units?
The standard units used by the international scientific community (International System of Units). It standardises measurements in the metric system.
What are the 2 types of SI unit?
*Base Unit
*Derived Unit
How many SI Base units are there?
7
What are the 7 SI Base Quantities?
*Mass
*Length
*Time
*Temperature
*Electrical current
*Amount of substance
*Light Intensity
What is the unit and unit symbol for mass?
kilogram, kg
What is the unit and unit symbol for length?
metre, m
What is the unit and unit symbol for time?
second, s
What is the unit and unit symbol for temperature?
Kelvin, K
What is the unit and unit symbol for electrical current?
Ampere, A
What is the unit and unit symbol for amount of substance?
Mole, mol
What is the unit and unit symbol for light intensity?
Candela, cd
What are derived units?
Any SI unit that is not a base unit, it is derived from the base units
What are examples of quantities with derived units?
Frequency, Hertz
Energy, Joule
Electric Charge, Coulomb
What is the standard form of pico-?
x10^-12
What is the standard form of nano-?
x10^-9
What is the standard form of micro-?
x10^-6
What is the standard form of milli-?
x10^-3
What is the standard form of centi-?
x10^-2
What is the standard form of deci-?
x10^-1
What is the standard form of kilo-?
x10^3
What is the standard form of mega-?
x10^6
What is the standard form of giga-?
x10^9
What is the standard form of tera-?
x10^12
What is hertz in base units?
Hz = S⁻¹
What is pascal in base units?
Pa = N/m²
= kg m s⁻² / m²
= kg m⁻¹ s⁻²
What is a joule in base units?
J = Nm
= kg m s⁻² m
= kg m² s⁻²
What is a watt in base units?
W = J/s
= kg m² s⁻² / s
= kg m² s⁻³
What is a coulomb in base units?
C = As
What is a volt in base units?
V = J/C
= kg m² s⁻² / As
= kg m² s⁻³ A⁻¹
What is an ohm in base units?
Ω = V/A
= kg m² s⁻³ A⁻¹ / A
= kg m² s⁻³ A⁻²
What is a newton in base units?
N = kg m/s²
= kg m s⁻²
What is the unit symbol for an astronomical unit?
AU
What is the unit symbol for a light year?
ly
What is the unit symbol for a parsec?
pc
What is a homogeneous equation?
A homogeneous equation is an equation in which every term has the same SI base units
What determines whether an equation is real?
For an equation to be real, it must be homogeneous
Is an equation correct if it is inhomogeneous?
No, if an equation is inhomogeneous it cannot be correct
Is an equation correct if it is homogenous?
Just because an equation is homogeneous does not mean it is correct, it can be correct or incorrect
Is the equation W = mg homogeneous and therefore valid?
W = N
m g = Kg N/Kg = N
Yes the equation has the same units for all components of the equation and is therefore homogeneous and valid
Is the equation v² = u² + 2as homogeneous and therefore valid?
v² = (ms⁻¹)² = m²s⁻²
u² = (ms⁻¹)² = m²s⁻²
2as = 2ms⁻²m = 2m²s⁻²
Yes the equation has the same units for all components of the equation and is therefore homogeneous and valid
Is the equation v² = 2u² + 2at homogeneous and therefore valid?
v² = (ms⁻¹)² = m²s⁻²
2u² = 2(ms⁻¹)² = 2m²s⁻²
2at = 2ms⁻¹
No, the equation is inhomogeneous and therefore is invalid
What is an astronomical unit?
The mean distance of the earth from the sun
What is a light year?
The distance travelled by light in a vacuum in one tropical year
What is a parsec?
A parsec is the distance at which an angle of one second of an arc will represent the distance of the earth from the sun
What is 0K in °C?
-273.15
What is the equation for % uncertainty?
(uncertainty / average value) x 100
What is an anomalous result?
An inconsistent reading which does not fit the trend
What is accuracy?
The degree to which a value obtained by experiment is close to the actual or true value
What is precision?
The degree to which repeated values, collected under the same experimental conditions, show the same results
What is absolute uncertainty?
The actual amount by which a quantity is uncertain, e.g 7 ± 0.5 cm
What are error bars?
Bars drawn on a graph to reflect uncertainty around each point on the graph
How do you use error bars in a line graph?
You draw the line of best fit along the plotted point, and then use the error bars to draw the 2 lines of worst fit (1 with the steepest gradient within the error bars and 1 with the shallowest gradient within the error bars)
What are the lines of worst fit?
The lines with the steepest and shallowest possible gradient that lie within the error bars
What is systematic error?
Error that is inherent in the experiment. Your measurements of the same thing will vary in predictable and consistent ways.
What is zero error?
A systematic error when a measuring system gives a false reading when the true value of a measured quantity is zero
What is parallax error?
A random error caused by a student not reading the measurement at eye level. It can lead to the reading being too high or too low.
What are examples of random error?
*Parallax Error
*Environmental Error
What are environmental errors?
Random and uncontrollable changes in an environment (such as temperature) that may cause the result to be inaccurate
What are environmental errors?
Random and uncontrollable changes in an environment (such as temperature) that may cause the result to be inaccurate
What is the rule of thumb for the absolute uncertainty on a measuring instrument?
half the finest division (if there is fluctuation in an electronic measurement, the finest division is the point which does not fluctuate)
How do you combine uncertainties when the quantities are added?
The uncertainty is the sum of the absolute uncertainties
How do you combine uncertainties when quantities are subtracted?
The uncertainty is the sum of the absolute uncertainties
How do you combine uncertainties when quantities are multiplied?
The total percentage uncertainty is the sum of the percentage uncertainties
How do you combine uncertainties when quantities are divided?
The total percentage uncertainty is the sum of the percentage uncertainties
When a quantity is raised to the power “n”, what do you do to the uncertainty
The total percentage uncertainty is n multiplied by the percentage uncertainty
What represents a vector quantity?
An arrow, the length represents the magnitude and the angle represents the direction
What is the resultant vector?
The resultant vector of an object is the vector that has the same effect as all the other vectors of the object combined
How do you add vectors acting at right angles to each other?
Use pythagoras’ theorum
How do you find the angle of the resultant vector?
Use trigonometry
What is resolving a vector?
Splitting a vector into its vertical and horizontal components
What are the 3 methods for adding non-perpendicular vectors?
- Draw a scale diagram
- Calculations using sine rule and cosine rule
- Calculations by resolving into horizontal and vertical components then using pythagoras’
2252N 48* under the horizontal
What is a scalar quantity?
A quantity with a magnitude but no direction
What is a vector quantity?
A vector quantity is a quantity with both magnitude and direction
How do you find the resultant force of parallel vectors?
Find the sum of the 2 vectors
What are parallel vectors?
They act in the same line and direction
What are antiparallel vectors?
They act in the same line but opposite direction
How do you find the resultant force of antiparallel vectors?
Find the sum of the 2 vectors
How do you calculate the absolute uncertainty from a set of data?
± half the range
To how many significant figures should you give absolute uncertainty?
1
A trolley has a weight of 11N and sits on a ramp inclined at 33* to the horizontal. How big is the component of the weight which is trying to pull the trolley along the ramp?
6N
A plumb bob has a weight of 1.0N. It is swinging on the end of a piece of string, and at one particular instant, the string is inclined at 28* to the vertical. What is the component of the weight perpendicular to the line of the string?
0.47N
A fly in a room is flying on a bearing of 204* at a speed of 0.36ms⁻¹. Sunlight streams horizontally westward across a room, forming a shadow of the fly on the west wall. How fast does the shadow move?
0.33 ms⁻¹
What is pythagoras’ theorem in 3d?
a² + b² + c² = d²
