INTRODUCTION - fill the blank for full credit
Pressure is the _____________ per unit _______________.

PROBLEM

How many pressure do you exert when standing on the ground with one foot ? Is it less or more than air pressure ?
air pressure is about  lb per in². That is,  if you weigh a column of air, 1 in x 1 in in area, from the ground to space,
you will find 15 lb. Who, among your group, exert the greatest pressure ? in the class ? in 9th grade?

PROCEDURE
materials: scale in pounds, ruler in inches, paper.
Each student of the team has to do it. Find out your weight in pounds. Stand on a piece of paper and have a lab partner trace the outline of your foot. Draw a rectangle that has about the same area as the outline.
Fill the table below.

student name	weigh in pounds (lb)	area in in2	pressure in lb/in2
=	=	=	=
=	=	=	=
=	=	=	=
=	=	=	=

ANALYSIS

1) Is it more or less than the air pressure ?

2) who exerts the greatest pressure in the team ? the class? the grade ? why?

GOING FURTHER try without hints

1) A woman weighs 495N and wears shoes that touch the ground over an area of 412 cm².
A) convert  412 cm² to m².  
hint: 1 cm = 0.01 m so 1cm² = 0.0001 m²
B) What is the average pressure in N/m² that is in Pa. (P = force / area )
pressure = ____ Pa
C) convert the pressure in kPa. P = _____ kPa
hint: divide by 1000
D) How does the pressure change when she stands on only one foot ? P = _______ Pa
hint: the area is divided by 2
E) What is the pressure if she puts all her weight on the hell of one shoe with the area of the heel of 2.0 cm²?
P = __________ Pa (don't forget to convert cm² to m² first : ) )


2) A car tire makes contact with the ground on a rectangular area of 12cm by 18cm. The car's mass is 925 kg. What pressure does the car exert on the ground? (follow the steps if you need help)
A)  find the weight of the car W  ________ N
B) find the area in cm2 then convert to m2. A = 12 x 18 cm² = __________ m²
C) Find the pressure P = W/A = ______ Pa

3) A Lead brick, 5.0 cm x 10.0 cm x 20.0 cm, rests on the ground on its smallest face.
What pressure does it exert on the ground (lead has a density of 11.8g/cm³).
Try on you own. Then check by following the steps.
A) find the mass (in grams) of the brick using it volume in /cm³ and its density in g/cm³.
 (hints: density = mass / volume      solve for mass in grams).
B) convert the mass in kilograms and find the weight (W) in newtons. (weight = mass x 9.8)
C) Find the area A of the smallest face in cm². (multiply the smallest dimensions).
D) convert the area A in m². (remember 1 cm² = 0.0001 m²)
E) Find the pressure in Pa (pressure = weight (N) / area ( m² )  )

4) What is the pressure exerted on the ground by a camera and tripod weighting 7.5 lb if each leg of the tripod has a tip whose area of contact with the ground is 0.05 in² . Give the answer in lb/in2 and don't forget a tripod has 3 legs !
(otherwise it would not be called a tripod !)