PiCAT key terms

The process by which green plants use sunlight, water, and carbon dioxide to make sugar and release oxygen. Chlorophyll in the leaves captures the light energy that drives the reaction.

How much mass is packed into a given volume of a material, usually calculated as mass divided by volume. A dense object feels heavy for its size and tends to sink in water.

A community of living things together with the nonliving surroundings they depend on, such as soil, water, and climate. Organisms in it interact through food chains and natural cycles.

The change of a liquid into a gas at its surface, which happens faster when the liquid is warm or exposed to moving air. It is one stage of the water cycle.

A number expressed as a part of 100. To find a percentage of a quantity, change the percent to a decimal and multiply, so 25% of 80 is 0.25 times 80.

A comparison of two quantities by division, often written as a fraction or with a colon. A ratio of 3 to 4 means three parts of the first amount for every four of the second.

The average found by adding all the values in a set and dividing by how many values there are. It is pulled up or down by unusually large or small numbers.

A rate in which the second quantity is one unit, such as miles per one hour or dollars per one pound. It makes comparisons easy because everything is measured against a single unit.

A word that has the same or nearly the same meaning as another word, such as quick and fast. Synonym questions ask you to choose the answer closest in meaning to the given word.

A word that means the opposite of another word, such as hot and cold. Antonym questions ask you to choose the answer that reverses the meaning of the given word.

A word part attached to the front of a root word that changes its meaning, such as un- in unhappy or pre- in preview. Knowing common prefixes helps you decode unfamiliar words.

A hint about a word's meaning that comes from the other words and sentences around it. Examples include definitions, examples, contrasts, and cause-and-effect statements in the passage.

The central point that a paragraph or passage is about, usually stated or hinted at in a single sentence. Every other sentence should support or explain it.

A conclusion you reach by combining information in the passage with what you already know, even though the writer does not state it directly. Inferences must be supported by the text.

A fact, example, or reason a writer includes to explain or prove the main idea. Details answer questions such as who, what, when, where, and why.

A whole number greater than 1 whose only factors are 1 and itself, such as 2, 3, 5, 7, and 11. Numbers with more factors, like 12, are called composite.

A letter or symbol that stands for an unknown or changing number in an expression or equation. Solving an equation usually means finding the value of the variable.

A small number written above and to the right of a base that tells how many times the base is multiplied by itself. In 3 squared, the exponent 2 means 3 times 3.

The total distance around the outside of a flat shape, found by adding the lengths of all its sides. For a rectangle it is twice the length plus twice the width.

The rule that in a right triangle the square of the hypotenuse equals the sum of the squares of the other two sides, written a squared plus b squared equals c squared. It finds a missing side.

The electrical pressure that pushes charges through a circuit, measured in volts. A higher voltage can push more current through the same amount of resistance.

The flow of electric charge through a conductor, measured in amperes. It is what actually does work in a circuit, such as lighting a bulb or turning a motor.

The opposition to the flow of electric current, measured in ohms. More resistance means less current for a given voltage, and some electrical energy is converted into heat.

A circuit in which all parts are connected in a single path, so the same current flows through every component. If one part breaks, the whole circuit stops working.

The burning of a fuel with oxygen to release heat and gases, which is what happens inside an engine cylinder. In a car engine, gasoline vapor mixed with air is ignited by the spark plug.

The gearbox and related parts that send power from the engine to the wheels at a suitable speed and force for driving conditions. It lets the engine run efficiently at different road speeds.

A belt-driven device that turns the engine's rotation into electricity to charge the battery and run the car's electrical systems while the engine is running.

A set of tubes and fins that releases engine heat into the air, cooling the liquid coolant that circulates through the engine. It is the main part of a car's cooling system.

A measuring tool with two adjustable jaws used to measure the inside, outside, or depth of an object. Many calipers have a scale or dial read to a fraction of an inch or a millimeter.

A cutting tool with flutes and a pointed tip that is turned by a drill to make round holes in wood, metal, or plastic. Its size and material must match the work.

A wrench that measures and limits how much twisting force is applied to a fastener, so bolts are tightened to a specified tightness without being overstressed or stripped.

The narrow slot of material removed by a saw blade as it cuts. It makes the cut slightly wider than the blade and must be allowed for when cutting to a marked line.

A rigid bar that turns on a fixed point to lift or move a load. A small force applied far from the pivot can balance a large load placed close to it.

The fixed point or pivot on which a lever turns. Moving the fulcrum changes the balance of force and distance, and therefore changes the lever's mechanical advantage.

A wheel with a grooved rim and a rope or belt running over it, used to change the direction of a pull or to lift heavy loads with less effort. Several pulleys increase the advantage.

The number of times a machine multiplies the effort force you put in. A machine with an advantage of 4 lets you lift a load with about one quarter of the force.

A turning of a figure or object around a point or axis. In assembly questions, a rotated part keeps its shape and proportions but faces a different direction.

A reversed copy of a shape, as if seen in a mirror, where left and right are swapped. A mirrored part cannot be turned into the original by rotation alone.

A drawing that shows the parts of an object pulled apart along their assembly lines, so you can see how they fit together and in what order they go.