Measurement and units
60 flashcards covering Measurement and units for the ACT Science section.
Measurement and units are the foundational tools scientists use to quantify the physical world around us. At its core, measurement involves assigning numerical values to properties like length, mass, volume, or time, using standardized units such as meters, grams, or seconds. This allows for precise communication and comparison in experiments and data analysis. Without consistent units, scientific observations would be chaotic and unreliable, making it essential for understanding everything from everyday phenomena to complex theories.
On the ACT Science section, measurement and units often appear in questions about interpreting graphs, analyzing experimental data, or performing calculations. You'll encounter tasks like converting between units (e.g., from miles to kilometers) or identifying errors in measurements, with common traps including mixing up imperial and metric systems or overlooking significant figures. Focus on accuracy in conversions and recognizing how units affect relationships in scientific contexts, as these skills help avoid mistakes on data-heavy questions.
Practice converting units quickly to build confidence.
Terms (60)
- 01
SI unit system
The International System of Units, a standardized set of units used in science for measurements of length, mass, time, and other quantities, based on seven base units.
- 02
Meter
The base SI unit for length, defined as the distance that light travels in a vacuum during 1/299,792,458 of a second.
- 03
Kilogram
The base SI unit for mass, defined as the mass of the international prototype kept at the International Bureau of Weights and Measures.
- 04
Second
The base SI unit for time, defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.
- 05
Ampere
The base SI unit for electric current, defined as the constant current that would produce a force of 2 × 10^{-7} newtons per meter of length between two straight parallel conductors of infinite length and negligible circular cross-section.
- 06
Kelvin
The base SI unit for thermodynamic temperature, defined as 1/273.16 of the thermodynamic temperature of the triple point of water.
- 07
Mole
The base SI unit for amount of substance, defined as the amount containing as many elementary entities as there are atoms in 0.012 kilograms of carbon-12.
- 08
Candela
The base SI unit for luminous intensity, defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 × 10^{12} hertz with a radiant intensity of 1/683 watt per steradian.
- 09
Kilo- prefix
A metric prefix meaning one thousand times the base unit, as in kilometer for 1,000 meters.
- 10
Milli- prefix
A metric prefix meaning one thousandth of the base unit, as in millimeter for 0.001 meters.
- 11
Centi- prefix
A metric prefix meaning one hundredth of the base unit, as in centimeter for 0.01 meters.
- 12
Micro- prefix
A metric prefix meaning one millionth of the base unit, as in micrometer for 0.000001 meters.
- 13
Conversion from Celsius to Kelvin
To convert a temperature from Celsius to Kelvin, add 273.15 to the Celsius value, as Kelvin is an absolute scale starting at absolute zero.
- 14
Conversion from Fahrenheit to Celsius
To convert a temperature from Fahrenheit to Celsius, subtract 32 from the Fahrenheit value and then multiply by 5/9.
- 15
Significant figures rules
Significant figures are the digits in a number that are known with certainty plus one estimated digit, and rules include that all non-zero digits are significant, zeros between non-zero digits are significant, and trailing zeros in a decimal are significant.
- 16
Scientific notation
A method of expressing very large or very small numbers as a value between 1 and 10 multiplied by 10 raised to a power, such as 6.02 × 10^{23} for Avogadro's number.
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Accuracy
The closeness of a measurement to the true or accepted value, indicating how correct the measurement is.
- 18
Precision
The closeness of repeated measurements to each other, indicating the consistency of the measurements.
- 19
Density formula
Density is calculated as mass divided by volume, with the formula density = mass / volume, and its SI unit is kilograms per cubic meter.
- 20
Speed formula
Speed is calculated as distance divided by time, with the formula speed = distance / time, and its SI unit is meters per second.
- 21
Velocity
A vector quantity that measures the rate of change of position with respect to time, including both speed and direction.
- 22
Acceleration formula
Acceleration is the rate of change of velocity over time, calculated as acceleration = change in velocity / time, with SI units of meters per second squared.
- 23
Force definition
Force is a push or pull upon an object resulting from its interaction with another object, measured in newtons, where one newton is the force needed to accelerate a one-kilogram mass at one meter per second squared.
- 24
Work formula
Work is calculated as force multiplied by distance in the direction of the force, with the formula work = force × distance, and its SI unit is joules.
- 25
Energy units
The SI unit for energy is the joule, which is equivalent to one newton-meter, representing the work done when a force of one newton acts over a distance of one meter.
- 26
Power formula
Power is the rate at which work is done or energy is transferred, calculated as power = work / time, with the SI unit of watts, where one watt is one joule per second.
- 27
Pressure definition
Pressure is the force applied per unit area, calculated as pressure = force / area, with the SI unit of pascals, where one pascal is one newton per square meter.
- 28
Atmospheric pressure
The pressure exerted by the weight of the atmosphere, typically about 101,325 pascals at sea level, often measured with a barometer.
- 29
Volume of a cube
The volume of a cube is calculated as the length of one side cubed, using the formula volume = side³, with units such as cubic meters.
- 30
Area of a rectangle
The area of a rectangle is calculated as length multiplied by width, using the formula area = length × width, with units such as square meters.
- 31
Dimensional analysis
A method for converting between units by multiplying by conversion factors, ensuring that units cancel out appropriately to solve problems.
- 32
Percent error calculation
Percent error is calculated as the absolute difference between the measured and accepted values, divided by the accepted value, then multiplied by 100, to express the accuracy of a measurement.
- 33
Mass
A measure of the amount of matter in an object, typically measured in kilograms, and it remains constant regardless of location.
- 34
Weight
The force exerted on a mass by gravity, measured in newtons, and it varies depending on the gravitational field strength.
- 35
Gravity on Earth
The acceleration due to gravity on Earth is approximately 9.8 meters per second squared, affecting the weight of objects.
- 36
Time measurement
Time is measured in seconds, minutes, hours, or other units, and it is a fundamental quantity in physics for describing rates of change.
- 37
Frequency
The number of cycles or occurrences per unit of time, measured in hertz, where one hertz is one cycle per second.
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Wavelength
The distance between successive crests or troughs in a wave, typically measured in meters, and it is inversely related to frequency.
- 39
pH scale
A logarithmic scale from 0 to 14 that measures the acidity or basicity of a solution, where pH = -log10[H+], and 7 is neutral.
- 40
Molarity
A measure of concentration defined as the number of moles of solute per liter of solution, with units of moles per liter.
- 41
Concentration
The amount of solute present in a given amount of solution or solvent, often expressed in units like molarity or percentage.
- 42
Specific gravity
The ratio of the density of a substance to the density of a reference substance, usually water at 4°C, and it is unitless.
- 43
Refractive index
A measure of how much a material bends light, calculated as the ratio of the speed of light in vacuum to the speed in the material, and it is unitless.
- 44
Density of water
The density of pure water at 4°C is 1 gram per cubic centimeter or 1,000 kilograms per cubic meter.
- 45
Speed of light
The speed at which light travels in a vacuum, exactly 299,792,458 meters per second, and it is a fundamental constant in physics.
- 46
Example: Converting miles to kilometers
To convert miles to kilometers, multiply the number of miles by 1.609, as one mile equals approximately 1.609 kilometers.
- 47
Example: Calculating density
If an object has a mass of 20 grams and a volume of 10 cubic centimeters, its density is 2 grams per cubic centimeter.
- 48
Common trap: Confusing mass and weight
Mass is the amount of matter and does not change with location, while weight is a force that depends on gravity, so they are not interchangeable.
- 49
Common trap: Significant figures in addition
When adding numbers, the result should have as many decimal places as the number with the fewest decimal places, to avoid overstating precision.
- 50
Formula for kinetic energy
Kinetic energy is calculated as one-half times mass times velocity squared, with the formula KE = 1/2 mv², and units of joules.
- 51
Potential energy
The energy an object possesses due to its position or state, such as gravitational potential energy calculated as mgh, where m is mass, g is gravity, and h is height.
- 52
Ohm's law
Ohm's law states that current through a conductor is directly proportional to the voltage and inversely proportional to the resistance, expressed as V = IR, with units of volts, amperes, and ohms.
- 53
Electric current
The flow of electric charge, measured in amperes, which is the amount of charge passing a point per unit time.
- 54
Voltage
The electric potential difference between two points, measured in volts, representing the energy per unit charge.
- 55
Resistance
A measure of opposition to current flow in a circuit, measured in ohms, and it depends on the material and dimensions of the conductor.
- 56
Wave speed formula
Wave speed is calculated as frequency multiplied by wavelength, with the formula speed = frequency × wavelength, and units of meters per second.
- 57
Period of a wave
The time for one complete cycle of a wave, measured in seconds, and it is the reciprocal of frequency.
- 58
Amplitude
The maximum displacement of a point on a wave from its equilibrium position, affecting the wave's energy and intensity.
- 59
Decibel level
A logarithmic unit that measures the intensity of sound, calculated as 10 times the logarithm of the ratio of sound intensity to a reference intensity.
- 60
Richter scale
A logarithmic scale that measures the magnitude of an earthquake based on the amplitude of seismic waves, where each whole number increase represents a tenfold increase in amplitude.