Activity 8. Title: Measuring Volume

Transcription

1 Activity 8 Title: Measuring Volume

2 Read A-32 Problem: How do you measure volume of a solid object? Hypothesis/Initial Thoughts:

3 Unit A Vocabulary Metric System The measuring system used by scientists and most countries other than the U.S. and United Kingdom

4 Unit A Vocabulary Volume The amount of space a material takes up ml or cm 3 1 ml = 1 cm 3

5 Unit A Vocabulary Water Displacement The amount or water that is moved (displaced). This determines the volume of the object that caused the water to be moved.

6 Units of Measure copy this into your notebook Length Mass Common Metric Unit centimeter (cm) meter (m) = 100 cm kilometer (km) = 1000 m gram (g) kilogram (kg) = 1000 g Basic Unit in SI meter kilogram Volume milliliter (ml) (1 ml = 1 cm 3 ) liter (L) = 1000 ml cubic centimeter (cm 3 ) cubic meter (m 3 ) cubic meter Base Unit (highlight)

7 Reading a Graduated Cylinder 1. Make sure it is on a flat surface 2. Bring your eye down to the same level of the fluid s surface. 3. Read the lowest point of the meniscus (the liquid s curve) 4. Estimate the volume in ml if it falls between marks.

8 Reading a Metric Ruler 1. Find cm and mm lines. 2. Make sure you are starting the measurement on the Zero line. 3. Estimate the length if it falls between marks. 4. Make sure your units are correct (cm or ml).

9 Significant Figures Depends on the level of accuracy of the measuring tool Consists of all digits know with certainty, plus one final digit

10 Two Methods to Determine Volume There are two methods to determine the volume of a solid object. You will learn both methods. Then will use your judgment to decide which method is the most appropriate to use for measuring particular objects.

11 Procedure: 1. Remove and observe the six objects from the cup 2. Predict the order of the objects from least to greatest volume. Record prediction. 3. Watch teacher demonstration of how to measure the volume of an object using two methods: Measurement and calculation Water displacement

12 Prediction: Which object has the greatest volume? Put a number on each object, ordering them from LEAST (1) to GREATEST (3) v = l w h or s 3 v = l wh v = πr 2 h r = ½ d Your calculated value cannot be more precise than the least precise measurement

13 Method 1: Measurement and Calculation Only works for objects that have regular shapes Measure and calculate using the appropriate formula Example: Measure the dimensions of the lt. gray bar l = 5.00 cm w = 1.25 cm h = 1.25 cm v = l wh v = 5.00 cm x 1.25 cm x 1.25 cm v = cm 3 v = 7.81 cm 3 hundredths Appropriate formula Least precise measurement is hundredths

14 Object Method Used Meas. Formula & Calc. Volume Light gray bar Meas cm 1.25 cm l =, w = h = 1.25 cm v = l x w x h = 5.00 cm x 1.25 cm x 1.25 cm 7.81 cm 3 Displ. v i = v f = v = =

15 Method 2: Water-Displacement How much do you think the water will rise when the light gray bar is put in it? Use a pipette to add or remove water so you can start with a convenient initial volume. Irregular objects cannot be measured, so you must use water-displacement. Volume = Final Volume - Initial Volume v = v final v initial OR v = v f v i (units are ml) v i = 30.0 ml, v f = 37.5 ml v = v f v i v = 37.5 ml 30.0 ml v = 7.5 ml

16 Object Method Used Meas. Formula & Calc. Volume Light gray bar Meas. l =, 5.00 cm w = 1.25 cm h = 1.25 cm v = l x w x h = 5.00 cm x 1.25 cm x 1.25 cm 7.81 cm 3 Displ. v i = 30.0 ml v f = 37.5 ml v f - v i v = = 37.5 ml 30.0 ml 7.5 ml

17 4. Divide objects into two sets, one dark grey & one light gray. Each pair begins with one set. 5. Determine which method is best for determining the volume. Use both methods for lt. gray cylinder & lt. gray bar. 6. Determine volume of each and record data in your table. 7. Exchange object sets and repeat steps 5 & Compare your results with the other pair in your group. Repeat anything you think is inaccurate. 9. Base on you data, list the objects from least to greatest volume. Record in notebook.

18 Discussion Were there any differences in your results for the volumes of the different objects? What do you think caused them? Error in measurements (reading the ruler or graduated cylinder incorrectly) Calculation errors Final Rankings Which was more accurate? Measurement and calculation because you did not have to round as closely. Water Displacement is best for irregular objects