How to Know if the experiment is valid.

Valid experiments 1.Have only 1 independent variable 2.Have one dependent variable that can be measured 3.Control all the known constants 4.Be testable

Valid experiment notes Background: In order for a scientific experiment to be acceptable, it must be valid. To be considered valid, a scientific experiment must meet the following requirements: 1.Have only one IV 2.Have one DV that can be measured 3.Control all other known constants 4.Be testable experiment.

Directions: Read the experiments explained below. Do the following: – Underline the experiment question. – Identify the IV and DV for the experiment and write them down. – If the experiment is valid circle the question number. – If the experiment is not valid, (1) explain what is wrong using the requirements above (2) along with what must be done to make the experiment valid.

1.Mrs. Cathey did an experiment to see how the size of the light bulb affects the amount of heat produced. Mrs. Cathey used a blue, red, and yellow light bulb in her experiment. She turned the light bulbs on for 40 minutes then used a thermometer to measure the temperature of the air 2 cm away from the bulbs. Below is a picture showing the light bulbs Mrs. Cathey used in her experiment. IV: ______________________DV:____________________ Size of light bulbAmount of heat 1. Not valid because more than one variable 2. Use the same color of lights

2.Mrs. Chapman did an experiment to see if the brand of food affects the growth rate of fish. She placed four fish in different 10 galloon tanks. Each fish was feed 1 gram of a different brand of fish food each day. She then measured the length of each fish. Below is the fish she used in the experiment. IV: Brand of fish foodDV: length of fish or growth of fish 1.Not valid b/c more than one independent variable 2.Same type and size fish

3.Mr. Wright used three of the same type of apple trees that were the same size in an experiment. He wanted to see what amount of water made the apples grow the fastest. The first tree he watered with 100 ml a day, the second tree he watered with 150 ml each day and the third he watered with 200 ml each day. He recorded the apples growth each day for four months. IV: amount of waterDV: number of apples grown