Sitting on Nails-Boyle's Law

Cieslik, Daniel Mather High School

Objectives: 1. To understand the difference between force and pressure. 2. To illustrate that pressure is a force per unit area. 3. To show pressure is a scalar while weight (i.e. force) is a vector quantity. 4. To show the relation between pressures above and below atmospheric pressure upon the volume of an enclosed gas when the temperature remains constant. (Boyle's Law) 5. To illustrate the graph of an inverse relation. 6. To show the effect of atmospheric pressure on a partial vacuum. Apparatus Needed: (Obj. 1-3) Three 1/2" plywood boards whose dimensions are 40 cm. x 20 cm. The first board has one nail in the center. The second has four nails in the center at the corners of a square about 6 cm. on a side. The third has 420 nails that are spaced 1 cm. apart, covering an area of 30 cm. x 15 cm. (Obj. 4 & 5) A modified hypodermic syringe used Boyle's Law Experiment similar to Science Kit and Boreal Lab. Cat. No. 64710. Take off the base and top of the syringe and suspend the syringe from a test tube clamp with the plunger up for positive pressure and with the plunger down for negative pressure. A series of standard laboratory weights are needed to provide the forces. (Obj. 6) The final part requires an empty ditto fluid can. Recommended Strategy: (Obj. 1-3) Ask students if they would sit on boards with one and four nails. Show the students the board with the 420 nails and ask them if they would sit on these nails. If you are not successful, you sit on the nails. At this point(s) you should also get one of the students to sit on the nails. (Obj. 4-6) Have the students collect data on the volume of air as a function of the pressure on the enclosed air. Have them graph their results. To illustrate the final objective take an empty ditto can with about a cubic centimeter of water in it; with the cover off the can heat it vigorously. Cover the can tightly and allow it to cool. After it is cooled, you take off the cap and blow up the can with your lung power.
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