A student drops one identical antacid tablet into 200 mL of vinegar at 10, 20, 30 and 40 degrees Celsius, timing how long each tablet takes to dissolve. Which quantity is the independent variable?

Three identical toy cars are released down the same ramp carrying 50 g, 100 g and 150 g of clay. The ramp angle and release point never change. Which quantity is the independent variable?

Bean seeds are planted in identical pots and given 0, 4, 8 or 12 hours of light a day, with the same soil and water. Which quantity is the independent variable?

A group wraps identical mugs of hot water in wool, foil, foam or nothing, then records each mug's temperature after 30 minutes. What is being manipulated in this design?

Water from one river is held at pH 5, 6, 7 and 8, each sample stocked with ten identical snails, and survival counted after one week. Which quantity is the independent variable?

A team runs the same electromagnet with 10, 20, 30 and 40 coil turns, using one battery and one iron nail throughout, and counts the paper clips it lifts. What is the independent variable here?

Students drop the same ball from 0.5 m, 1.0 m, 1.5 m and 2.0 m onto the same floor and measure the bounce height each time. Which quantity belongs on the horizontal axis of their graph?

For a month, a class records the cloud cover and rainfall over their school each morning. They change nothing and compare their school with no other place. Which type of investigation is this?

Students measure the dissolved oxygen in a fast stretch and a slow stretch of the same stream on one morning, altering nothing about either stretch. What kind of investigation are they carrying out?

A team adds 0, 5, 10 and 15 g of salt to identical containers of water and records the freezing temperature of each container. Which type of investigation is this?

A biologist lists every plant species growing in one meadow across a summer, adding nothing to the meadow and surveying no other site. How is this investigation best described?

A class weighs the litter collected from the cafeteria and from the gym every Friday for six weeks. Nothing in either room is altered. Which label fits this investigation?

Five identical seedlings get 10, 20, 30, 40 and 50 mL of water a day with the same soil and light. After two weeks each plant's leaves are counted. Which quantity is the dependent variable?

A student rolls the same marble from the same ramp across carpet, tile, sand and grass, then measures how far it travels on each surface. Which quantity is the dependent variable?

Identical iron nails sit in air, tap water, salt water and oil for ten days, and each nail is weighed at the end. Which quantity is the dependent variable?

Four identical bulbs run on 1, 2, 3 and 4 batteries, and a light meter reads how bright each bulb is. Which quantity belongs on the vertical axis of the results graph?

A team tests four fin shapes on the same model rocket, launching each shape three times from one launcher and stopping a timer when the rocket lands. Which quantity is the dependent variable?

Bread slices are stored at 5, 15 and 25 degrees Celsius in identical sealed bags, and students count the mold spots on each slice after a week. Which quantity is the dependent variable?

A team tests whether a paper plane's shape changes its flight distance. Four designs are folded from the same paper and thrown down one hallway. Which quantity must stay the same across throws?

Students test whether water temperature affects how fast sugar dissolves, stirring one sugar cube into 200 mL of water at four temperatures. Which quantity should be held constant?

A class investigates whether soil type changes how quickly water drains through it. They pour water into four funnels holding different soils. Which condition should be identical in every funnel?

To test whether magnet strength depends on distance, a student holds one magnet at 1, 2, 3 and 4 cm from a ball and reads the pull on a force meter. What must stay the same?

A study asks whether background music changes how well students recall word lists. Two groups take the recall test in different rooms. Which condition must be matched between the groups?

Two students compare battery brands by timing how long each battery keeps a flashlight lit. Which factor has to be identical for the comparison to be fair?

A group tests whether ramp surface changes a cart's speed, timing the same cart down carpet, wood and sandpaper ramps. Which quantity should not change from run to run?

Students fill Cup A with 100 mL of hot water and Cup B with 50 mL of cold water, then record how much each cools in ten minutes. Why can this not settle which cup insulates better?

A gardener sprays Fertilizer X on plants beside a sunny window and Fertilizer Y on plants in a dim corner. The window plants grow taller. Why can Fertilizer X not be credited?

One class studies with flashcards for 40 minutes, and another studies a different chapter with notes for 15 minutes. The flashcard class scores higher. Why can flashcards not be credited?

A student runs 100 m in Brand A shoes on a flat track, then in Brand B uphill on gravel while carrying a backpack. Why can he not conclude that Brand A is faster?

A team leaves one nail in salt water for two weeks and a second nail in fresh water for two days. The salt-water nail rusts more. Why is this comparison not convincing?

A shop claims its new 9 W bulb uses less energy than an old 60 W bulb. It runs the new bulb for 3 hours and the old bulb for 12 hours, then adds up the energy each used. Why does this not settle the claim?

Group 1 pours pond water through a new filter. Group 2 pours tap water through no filter. Group 2's water ends up clearer. Why can the groups not judge the filter?

A class times one paper plane flight at 3.2 s, then repeats the throw nine more times with the same plane and averages all ten times. What does averaging the ten throws give them?

Instead of planting one seed at each fertilizer level, a team plants 30 seeds at every level and averages the growth. What does the larger sample mainly buy the team?

Three different schools run the same cooling investigation with the same procedure and obtain similar results. What does this replication add to the original finding?

A student's five timings of the same falling ball are 1.1, 1.2, 1.1, 2.9 and 1.2 seconds. What should the student do about the 2.9 s value before reporting a result?

A company tests whether a vitamin drink speeds recovery. Forty runners drink it after identical training. Forty more runners are set aside for comparison. How should the second forty be treated?

In a test of a new plant growth lamp, one tray of seedlings sits under the lamp. What is the purpose of a second identical tray grown under the room's ordinary light?

Students test whether an antibacterial soap reduces bacteria on hands. Ten volunteers wash with that soap. What should the ten volunteers in the comparison group do?

A team adds a chemical to pond water to test whether it kills algae. They also keep one jar of the same pond water with no chemical added. Why does that untreated jar matter?