Accuracy, Precision, and Proportional Values

1. Accuracy, Precision, and Proportional Values Mrs. Nielsen Chemistry

2. Accuracy vs. Precision Accuracy: Measures how close measurements are to the correct value. Precision: Measures how close a set of measurement quantities are to one another. • High accuracy • High precision • Low accuracy • High precision • Low accuracy • Low precision • High accuracy • Low precision

3. How can we describe a pitcher’s throws during a baseball game using accuracy and precision? Food for thought:

4. value actual – value measured X 100 % Error = value actual mass measured % Yield = X 100 mass actual How do scientists determine the accuracy of their measurements?

5. Mass Density = Volume constant Proportional Values 1) Directly Proportional: Question: If mass increases x2, what must happen to volume? Answer: Volume must also increase x2!

6. x2 x2 ÷2 ÷2 So, we can say that mass and volume are directly proportional. In other words, they change by the same magnitude when density is held constant. Ex) The density of Al is 2.7 g/cm3. Finish the table below. 108.8 27.2

7. constant Proportional Values 2) Indirectly (Inversely) Proportional: Distance = velocity x time Question: If I increase my velocity on a trip to Las Vegas, will the time it takes to get there increase or decrease? Answer: The time will decrease!

8. Ex) If I am driving a distance of 100 miles, how long will it take me to get there if I am traveling: 25 mph? 50 mph? 100 mph? So, we can say that velocity and time are indirectly (inversely) proportional. In other words, when one value increases, the other decreases when distance is held constant. 4 hours 2 hours 1 hour