A statement reads: in every measured chemical reaction, the total mass of the products equals the total mass of the reactants. What kind of statement is this?

Scientists once held that continents were fixed in place. Sea-floor spreading data later led to plate tectonics replacing that view. Why did the accepted explanation change?

A student writes: 'If I stir the water, the sugar will dissolve faster,' and then plans an experiment to test it. What is this statement?

A website says a bracelet's 'energy field' cures colds, offers only customer stories as support, and states that no instrument can detect the field. Why is this claim pseudoscientific?

A textbook explains that all matter is made of tiny moving particles, and that this accounts for pressure, diffusion and changes of state. What is this explanation?

In science, how does a law differ from a theory?

A team drops the same ball from 1.5 m onto tile, carpet, cork and rubber, and records how high it bounces. Which quantity is the dependent variable?

Students compare how quickly sugar dissolves in water at 20 C, 40 C and 60 C. Which step keeps the test fair?

To test whether a fertilizer speeds bean growth, a class grows 20 bean plants with fertilizer. What must the class add to make the comparison valid?

A group times one paper plane flight at 4.2 s and reports that as the design's flight time. Why should they fly the plane several more times?

A second class repeats an investigation using the same procedure and gets results close to the first class's. What does this add to the finding?

A student tests whether music helps memory. She plays music for group A in a quiet room and gives group B no music in a noisy hallway. What flaw does this design have?

Two bridge designs are built from the same materials. How should a team test which design holds more mass?

Students ask whether darker soil warms faster in sunlight. Which measurement answers their question?

Look at the graph of a car's distance from school. During which interval was the car not moving?

Look at the graph of water drained by four soils in ten minutes. Which soil drained the least water?

Look at the table of temperatures measured before and after a reaction. What does the data show about the reaction?

A bean plant was 2 cm on day 4, 5 cm day 8, 9 cm day 12, 10 cm day 16, 10.5 cm day 20. What happened to its growth rate after day 12?

Timing a trolley down a ramp gives 2.1 s, 2.3 s, 2.2 s, 2.4 s and 2.0 s. What is the mean time?

A student reads the thermometer standing in a beaker of warm water. What temperature does it show?

Look at the table of lifting test results for four designs. Which statement about the data is accurate?

A cart moves at a steady speed and covers 12 m in 4 s. What is its speed?

A class measures the boiling point of water once, with one thermometer, and records 97 C. What is the best next step?

One group's mass reading is far from the readings all five other groups obtained for the same object. What should that group do first?

Students time a pendulum's single swing of about 1.5 s by hand with a stopwatch. What is the largest source of error here?

A survey of 12 students in one class finds that 9 walk to school. The report concludes that most students in the country walk to school. What limits this conclusion?

A student models an atom by drawing electrons as dots on neat circles around the nucleus, all circles evenly spaced. Which feature of a real atom does this model fail to show?

A class models the water cycle with a sealed jar of warm water under a chilled lid, and drops form on the lid and fall. Which limitation does this model have?

Look at the meadow food web diagram. What does it show about the hawk?

A model of the Earth-Moon system uses a basketball for Earth and a tennis ball for the Moon, set 30 cm apart on a desk. Which feature does this model get wrong?

A claim states that the total mass of a sealed system stays the same during a chemical reaction. Which measurement supports that claim?

Over 30 years a moth population on soot-darkened trunks shifts from 90 percent pale to 15 percent pale. Birds hunting by sight eat the moths they can see. Which claim does this evidence support?

After the same push, a ball rolls 4.2 m on a smooth floor and 1.3 m on carpet. The claim is that friction slows the ball. What is the reasoning?

Students report: the bell inside the jar grew silent as the air was pumped out; sound needs matter to travel. Which part of this report is the evidence?

A water filter brief says it must remove visible dirt, produce clear water, filter 1 L in under 5 minutes, and be built only from classroom materials. Which of these is a constraint rather than a criterion?

A brief requires a model car to travel 3.0 m in under 4.0 s using kit parts only. Look at the test results. Which car meets the whole brief?

A team's prototype bridge collapses under 400 g, but the brief requires it to hold 600 g. What is the next step in the design process?

A brief caps a phone case at 8 mm thick and requires it to survive a 1 m drop. A foam case survives the drop but measures 11 mm. What should the team do?

A student is about to heat a solution that gives off irritating fumes. Where should this heating be done?

A student must find the mass of 25 mL of a liquid. Which pair of items does the task call for?