Sitting on Nails-Boyle's Law

Cieslik, Daniel             Mather High School 
                            989-3550
                           

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.