2. The Physical Sciences

3. Chapter Two: Science and Measurement
2.1 Inquiry and the Scientific Method
2.2 Distance, Time, and Speed
2.3 Experiments and Variables

4. Investigation 2B
Speed
Which ramp is fastest?

5. 2.2 Variables
When scientists need to communicate precise information they use variables.
A variable is a well-defined piece of information with a name and a value.
The variable depth represents all possible values for the distance between the surface and the submarine.

6. 2.2 Speed
We use the variable speed to describe how quickly something moves.
Saying a race car, runner, or plane is “fast” is not enough to accurately describe its speed scientifically.

7. 2.2 Speed
The speed of a bicycle is the distance it travels divided by the time it takes.

8. 2.2 Average Speed
The speed found by dividing the total distance by the total time is the average speed.

9. 2.2 Constant speed
Constant means “does not change” so constant speed is speed that does not change.
How do we know the speed of the bike is constant?

10. 2.2 Units for speed
Since speed is a ratio of distance over time, the units for speed are distance units over time units.

11. 12.2 Relationships between distance, speed and time
An equation can be used to calculate speed, distance, or time if two of the three values are known.

13. 2.2 Calculating Speed
To use a formula, remember that the words or letters stand for values that the variables have.
You can think of each letter as a box that will eventually hold a number.

14. 2.2 Comparing Variables
In order to compare variables they must be in the same units.
To convert between units, you multiply and/or divide by conversion factors.
A conversion factor is an equivalent ratio.

15. 2.2 Using conversion factors
Conversion factors are translators between one language of units and another.

17. 2.2 Solving design problems
Write down very clearly everything your solution needs to accomplish.
Write down every constraint that must also be met..
Think up an idea that might work.
Follow the design cycle.
What should you do if your protype fails the test?