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Identifying Variables & Designing Investigations

Identifying Variables & Designing Investigations. Variables are things that vary and change. 3 Kinds of Variables. Independent Variable – something that is changed by the person performing the experiment What is tested What is manipulated. Example:.

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Identifying Variables & Designing Investigations

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  1. Identifying Variables&Designing Investigations

  2. Variables are things that vary and change

  3. 3 Kinds of Variables • Independent Variable – something that is changed by the person performing the experiment • What is tested • What is manipulated Example: Investigating how a weight affects the length of an elastic band. You decide the weight to apply, so: Weight is the independent variable.

  4. 3 Kinds of Variables • Dependent Variable – something that might be affected by the change in the independent variable • What is observed • What is measured Example: Investigating how a weight affects the length of an elastic band. You measure the resulting length of the elastic band, so: Length is the dependent variable.

  5. 3 Kinds of Variables • Controlled Variable – a variable that is not changed • Also called constants • Allow for a “fair test” in order to see relationships between independent & dependent variables Example: Investigating how a weight affects the length of an elastic band. You must use the same elastic band all the time, and the same scale etc,soit is a fair test.

  6. Control Group Some experiments call for a group in which nothing is changed so that it can be used for comparison SpongeBob’s Flower Power experiment – flower that did not receive the special fertilizer

  7. For Example:

  8. Identify the variables in this investigation. • Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle. • Independent variable: • Dependent variable: • Controlled variables:

  9. What was the independent variable? • Ages of the students • Different ages were tested by the scientist

  10. What was the dependent variable? • The time it to put the puzzle together • The time was observed and measured by the scientist

  11. What was a controlled variable? • Same puzzle • All of the participants were tested with the same puzzle. • It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

  12. Another example:

  13. Identify the variables in this investigation. • The higher the temperature of water, the faster an egg will boil. • Independent variable: • temperature of water • Dependent variable: • time to cook an egg • Controlled variables: • type of egg

  14. Designing Investigations

  15. Design an investigation for each and identify the variables: Test whether hot or cold water freezes first Test whether sugar packs cause cut flowers to last longer Test to see whether height of a pendulum affects the number of swings per minute Test to see if the amount of soap in a soap water mixture affects the size of a soap bubble Test to see whether the type of surface affects the speed of a rolling object

  16. Test whether hot or cold water freezes first Temp. of water Time it takes water to freeze Container, type of water, freezer, placement in freezer Put two cups filled with the same amount of water into the freezer. Check the water every 10 minutes to note which cup of water freezes first. Independent variable: Dependent variable: Control variables:

  17. Test whether sugar packs cause cut flowers to last longer Type of water Health of flower Type of flower, vase, amount of sunlight, type of water, type of sugar Take two bunches of cut roses into two vases one with just water and the other with the sugar mixed into the water. Check the flowers every day noting how healthy they look. Independent variable Dependent variable Controlled variables

  18. Test to see whether height of a pendulum affects the number of swings per minute Height of pendulum Number of swings per minute Mass at end of pendulum, length of cord, timing of swings per minute Hold the bottom of the pendulum 10 cm above the table top and let go, counting the number of swings in a minute. Repeat with 20 cm, 30 cm, and 40 cm. Independent variable Dependent variable Controlled variables

  19. Test to see if the amount of soap in a soap water mixture affects the size of a soap bubble Amount of soap in water Diameter of bubbles Amount of water, type of soap, way of measuring diameter of bubble, equipment used to blow bubble, person blowing bubble Make different soap water solutions with different amounts of soap but same amount of water. Blow bubbles and measure the diameter of the bubbles. Independent variable Dependent variable Controlled variables

  20. Test to see whether the type of surface affects the speed of a rolling object Type of floor surface Speed of rolling object Car, ramp, distance Roll a toy car down a ramp onto a tile floor. Measure the distance and time of the car and calculate the speed. Repeat experiment using 5 different floor surfaces. Independent variable Dependent variable Controlled variables

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