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Vocabulary: The Processes of Physics
The goal of physics: To describe and explain patterns in the natural world.
Divvying up the natural world
Object: Anything in the universe whose internal structure, if it exists, is being ignored.
Example: A baseball has internal structure, but we can ignore its structure when determining whether a hit is a home run.
The word “particle” is sometimes is used in place of the word “object,” especially when the object’s volume is negligibly small.
Particle: An object of negligible volume.
Fundamental particle: An object with no discernable internal structure.
An electron is a fundamental particle. Protons and neutrons are not, as they are made of smaller particles called quarks and gluons. You ignored the internal structure of protons and neutrons in chemistry, and treated them as objects.
Extended object: An object whose size, shape, and density are important in defining relevant properties, such as moment of inertia.
System: A collection of objects whose internal structure is being studied.
Example: To fix an engine, we must take it apart, meaning it has to be treated as a system.
Environment: A region of the universe outside of a system which might interact with the system.
Model: A simplified representation of part of the natural world.
Model: A simplified representation of part of the natural world.
A simple pendulum is a model of actual pendulums. It works well when almost all of the mass of the pendulum is at the bottom of the string. We assume that the string has no mass, and use force or energy concepts to determine the behavior of the pendulum.
Dude, do you even measure?
Measurement: Comparison of an unknown quantity to a better-known quantity.
Example: The lengths marked on a ruler are better known that those of the object being measured, but the ruler is not perfect, leading to measurement uncertainty.
Property: An attribute of an object or a system that is measurable.
Example: The capacity of a soda bottle might be 2.0 Liters. Capacity is the property…
Quantity: An amount associated with a property.
…and 2.0 Liters is the quantity. Important properties / quantities in physics include distance, time, mass, acceleration, force, energy and momentum.
Systems are often more than the sum of their parts. They have properties which disappear when the system is disassembled. For example, water is a liquid with a number of important physical properties. Its components, hydrogen and oxygen, are both gases.
Accurate: In agreement with an accepted value.
Precise: In agreement with other similar data.
Calibration: The marks on a measuring instrument.
Limit of calibration: The value of the smallest space between marks on the measuring instrument.
Doubtful digit: For analog devices, an additional place value determined by estimating between calibration marks.
Ch-ch-changes
Interaction: Event in which objects or systems influence each other.
Quantities possessed by objects may change as a result of an interaction. For example, a car accident changes the speeds of the cars. (cars = objects, accident = interaction, speed = property).
Interactions typically involve forces (pushes and pulls).Trend: A predictable change in one or more quantities.
Relationship: A mathematical rule describing a connection between two quantities.
Variable: Quantity that might change during an experiment.
Independent variable: The variable whose value is changed by the experimenter.
Dependent variable: The variable that might be affected by changing the independent variable.
Control variables: Variables whose values are purposely kept constant during an experiment, to avoid possible influences on the dependent variable.
It's the law
Law: A description of observed events that combines many individual observations into a general rule.
Conservation law: Rule that defines how objects interact in which a total quantity remains constant.
Examples: Conservation of energy, conservation of mass, conservation of charge and conservation of momentum.
Systems can be closed or open with respect to a given quantity.
Closed system: The quantity remains constant over time. There are no interactions that result in a quantity increase or decrease.
Open system: The quantity changes due to interactions with other objects or systems. If the quantity is conserved, the change in quantity possessed by the system equals the amount transferred to or from the system.
Example: A perfect thermos bottle at rest on a table would be a closed system for energy… no energy in or out. In reality, no thermos bottle is perfect, so the system (the thermos and hot liquid inside) loses energy to the air around the bottle.
Isolated system: There are no interactions with outside objects or systems. No external forces are present.
Staking a claim
Statement of problem: A description of the possible relationship or trend to be investigated, including the relevant variables, often stated in the form of a question.
Example: How are engine power and vehicle weight related to the acceleration of an automobile?
Claim: A prediction of a possible relationship or trend present in a specific situation, never stated in the form of a question.
Example: For automobiles, engine power is directly related to acceleration if other variables are held constant.
Claims must be specific. To say that all objects fall down is not a claim, but to say that all objects near the Earth’s surface accelerate at the same rate is a claim.
Hypothesis: A testable claim used in scientific inquiry (in an experiment or in research).
The outcome of an experiment will tend to confirm the hypothesis, or to refute it, or the results will be inconclusive. All of these outcomes are useful.
Explanation: A specific statement addressing why something that is observed occurs, possibly including a cause-and-effect relationship or mechanism of change.
Example: Fast moving particles have enough kinetic energy to break free from the surface of a liquid.
Theory: A combination of many related explanations, all shown to be reliable, into a general statement or model.
Example: Atomic theory, our model for the structure of the atom that includes protons, neutrons and electrons, unifies many individual explanations of atomic behavior in chemistry and physics.
Theories are well tested and highly reliable, however, they may be incomplete or require modification over time. Theories are never “proved” or shown to be absolutely true, since doing so would require that every possible related experiment be conceived of and run.
Laws are NOT well-proven theories. Laws are different from theories. Laws describe a predictable pattern in nature, while theories explain such patterns by fitting them into a wide-ranging model.
Scientific laws and theories are the most certain facts known to humankind.