Lesson: Measuring Volume of Irregular Objects
DO NOW: Show students a rock or some other irregular object and ask them to come up with a method to measure its volume. Review.
Ask: Have you ever entered a swimming pool or a bathtub and had the water rise? Ask them why this happens.
Answer--you take up volume (space) so the water level rises to reflect this.
State: Scientists use a similar method to measure the volume of objects that are irregularly shaped. The volume of a rectangle is relatively easy to calculate, just measure the 3 sides and mulitply. An irregular object, however, if difficult to measure in this way because the sides are equal. Therefore, we need to use a method called water displacement. If you can read a graduated cylinder and subtract, then you can figure out the volume of an irregular object.
Example: Draw 2 graduated cylinders on the board. Label one with 100mL of water and another with an object in the grad. cylinder and a volume of 150mL. Ask what the volume of the object is. Answer: 50mL or 50cm cubed.
Next: Handout (Classwork worksheet 1) and have students complete with a partner. You can project the worksheet on the board too with an LCD projector. You may want to model a few examples before having them complete the worksheet.
Steps for measuring the volume of an irregular object:
1) Pour a set amount of water into grade cylinder (100mL)
2) Gently slide the object into the grad. cylinder
3) Take the new volume reading
4) Subtract the 100mL from the new volume and that is the volume of the irregular object.
Next: Review classwork with the class. You could have students come up to the board and explain, using the LCD projector, how they derived their answer. Address any confusion.
Homework: Have students create a cartoon that explains how the water displacement process works.
|Classwork worksheet 1 Classwork||