Educational worksheet for identifying independent, dependent, and constant variables in scientific experiments.

Let's go through each item and identify the Independent Variable (I), Dependent Variable (D), and Constants (C).

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Definitions:

- Independent Variable (I): The variable that is deliberately changed or manipulated by the experimenter.
- Dependent Variable (D): The outcome that is measured; it depends on the independent variable.
- Constants (C): Factors that are kept the same throughout the experiment to ensure a fair test.

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1. A study was done to find if different tire treads affect the braking distance of a car.

- I: Type of tire tread
- D: Braking distance
- C: Car model, speed, road conditions, driver, weight of car, brake condition

> *Explanation:* Tire tread type is what’s being changed. Braking distance is what’s being measured. Other factors must stay constant to isolate the effect of tire tread.

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2. The time it takes to run a mile depends on the person’s running speed.

- I: Running speed
- D: Time to run a mile
- C: Distance (1 mile), terrain, weather, footwear, fitness level (if controlled)

> *Explanation:* Speed is varied; time is the result. Distance is fixed at one mile, so it's a constant.

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3. The height of bean plants depends on the amount of water they receive.

- I: Amount of water
- D: Height of bean plants
- C: Type of plant, soil, sunlight, temperature, pot size, seed quality

> *Explanation:* Water amount is manipulated; plant height is measured. All other growing conditions should be held constant.

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4. The higher the temperature of the air in the oven, the faster a cake will bake.

- I: Oven temperature
- D: Baking time (or how fast the cake bakes)
- C: Cake recipe, oven type, pan size, ingredient amounts, humidity

> *Explanation:* Temperature is changed; baking time is observed. Recipe and equipment remain constant.

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5. Lemon trees receiving the most water produced the most lemons.

- I: Amount of water
- D: Number of lemons produced
- C: Tree variety, sunlight, soil type, fertilizer, age of tree

> *Explanation:* Water is varied; fruit yield is measured. Other factors affecting growth should be constant.

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6. An investigation found that more bushels of potatoes were produced when the soil was fertilized more.

- I: Amount of fertilizer
- D: Bushels of potatoes produced
- C: Soil type, planting depth, water, sunlight, potato variety, spacing

> *Explanation:* Fertilizer amount is manipulated; potato yield is measured. Other growing conditions are kept consistent.

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7. Students measured the temperature of the water at different depths in Lake Skywalker and found that the temperature varied.

- I: Depth of water
- D: Water temperature
- C: Location in lake, time of day, season, weather conditions

> *Explanation:* Depth is the variable being tested; temperature is the response. External conditions should be constant for accurate comparison.

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8. The amount of pollution produced by cars was measured for cars using gasoline containing different amounts of lead.

- I: Amount of lead in gasoline
- D: Amount of pollution produced
- C: Car model, engine type, driving conditions, speed, fuel efficiency, distance traveled

> *Explanation:* Lead content in fuel is changed; pollution output is measured. Car and driving conditions must be constant.

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9. Four groups of rats are first massed and then fed identical diets except for the amount of vitamin A they receive. Each group gets a different amount. After 3 weeks on the diet, the rats' masses are measured again to see if there has been a decrease.

- I: Amount of vitamin A in diet
- D: Change in rat mass (or final mass)
- C: Diet (except vitamin A), initial mass, environment, cage conditions, water, light cycle, duration of experiment

> *Explanation:* Vitamin A amount is varied; change in body mass is measured. All other dietary and environmental factors are kept constant.

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✔ Final Answers:

| # | I | D | C |
|---|---|---|---|
| 1 | Type of tire tread | Braking distance | Car model, speed, road conditions, driver, weight, brakes |
| 2 | Running speed | Time to run a mile | Distance (1 mile), terrain, weather, footwear |
| 3 | Amount of water | Height of bean plants | Plant type, soil, sunlight, temperature, pot size |
| 4 | Oven temperature | Baking time | Cake recipe, oven type, pan size |
| 5 | Amount of water | Number of lemons | Tree variety, sunlight, soil, fertilizer |
| 6 | Amount of fertilizer | Bushels of potatoes | Soil type, water, sunlight, potato variety |
| 7 | Depth of water | Water temperature | Location, time of day, season |
| 8 | Amount of lead in gasoline | Pollution produced | Car model, driving conditions, fuel efficiency |
| 9 | Amount of vitamin A | Change in rat mass | Diet (other than vitamin A), environment, initial mass |

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