Physical Science and You

2. Physical Science and You • Chapter One: Studying Physics and Chemistry • Chapter Two: Experiments and Variables • Chapter Three: Key Concepts in Physical Science

3. Chapter Two: Experiments and Variables • 2.1 Variables and Relationships • 2.2 Experiments and Data

4. Investigation 2A Systems and Variables • How do scientists find relationships in nature?

5. 2.1 Variables and Relationships • A variableis a quantity that has a valuewhich describes something. The variable color represents all possible choices and red is a value, a specific choice of color.

6. 2.1 Variables and Relationships • Which is the variable and which is the value?

7. 2.1 Using Variables in Physical Science • Consider the experiment with a car that rolls down a straight track. • What variables affect the motion of the car in this system?

8. 2.1 Using Variables in Physical Science • Some common variables in physical science include: • mass • time • position • angle • temperature • volume

9. 2.1 Using Variables in Physical Science • Physical science is all about relationships between variables. • A good way to show a relationship between two variables is to use a graph.

10. 2.1 Using Variables in Physical Science • A graph is a mathematical diagram that shows: • one variable on the y (vertical) axis • a second variable on the x (horizontal) axis.

11. 2.1 Using Variables in Physical Science • Two variables may have: • a strong relationship, • a weakrelationship, • or no relationship at all.

12. 2.1 Direct Relationships • In a direct relationship, when one variable increases, the other also increases. • This is also called a linear relationship.

13. 2.1 Inverse Relationships • In an inverse relationship, when one variable increases, the other decreases.

14. 2.1 Complex Relationships • Some relationships are neither direct nor inverse. • This graph shows a non-linear relationship.

16. 2.1 Designing a graph • A graph makes it easy to see if changes in one variable cause changes in the other variable (the effect). • The variable that causes the change is called the independent variable. • The dependent variableshows the effect of changes in the independent variable.

18. 2.1 Designing a graph • The independent variable is always placed on the x-axis. • The dependent variable is always placed on the y-axis.

19. 2.1 Reading a graph • A graph is a simple form of model that connects two or more variables. • Scientists use models to make and test predictions.

20. 2.1 Four steps to make a graph Step 1:Choose which will be the dependent and independent variables. The dependent variable goes on the y-axis and the independent variable goes on the x-axis. Step 2:Make a scale for each axis by counting boxes to fit your largest value. Count by multiples of 1, 2, 5, or 10. Step 3:Plot each point by finding the x-value and drawing a lin upward until you get to the right y-value. Step 4:Draw a smooth curve that shows the pattern of the points. Do not just connect the dots.

21. 2.1 Using math to describe variables • Math is the best language to describe relationships between variables. • When you write out a relationship in math, you use a single letter or symbol to represent each variable. • We can show the relationship between variables for volume in two different ways.

23. 2.1 Basic Math Operations • The relationships between variables are represented in math by operations. • Four operations you know are: • add • subtract • multiply • divide.

24. 2.1 Solving for one variable • Formulas allow you to calculate any one variable if you know the values of the others.

25. 2.1 Basic Math Operations • A formula is a relationship that gives one variable in terms of other variables.

26. Activity Guess the Gram • Use a triple beam balance to measure mass and to estimate the masses of everyday objects.