PROBLEMS 45 



All forces are, quite literally, ''factors of energy." Thus, a generalized 

 driving force times a quantity yields energy. Some examples are: 



Mechanical force x distance = mechanical energy or work 



Gas pressure x volume of gas = mechanical energy or work 



Osmotic pressure x molar volume = osmotic energy or work 



Electrical potential x charge = electrical energy or work 



Temperature x entropy = heat energy or work 



Chemical potential x concentration = chemical energy or work 



The inherent difficulties of considering both temperature in "degrees" 

 (fractions of a length of a liquid metal along a tube!) and chemical poten- 

 tial (actually an energy per unit concentration) as "forces," are expounded 

 further in Chapter 7. 



What happens to a biological system when the force responsible for the 

 acceleration due to gravity (g) is removed — that is, becomes weightless — is 

 critically important to future space travel. The meager information on the 

 few human beings who have so far orbited the earth is reviewed in Chapter 8. 



PROBLEMS 



2-1 : A 200-lb football player is running full speed at a rate of 100 yd in 12 sec. Cal- 

 culate his kinetic energy in ergs; in joules; in calories; in Calories or kilocalories. 

 If he were stopped completely in 1 sec, what power would he deliver during 

 that 1 sec (in watts; in horsepower; in Cal/hr)? Compare this with the basal 

 metabolic rate of 0.1 hp, or 60 Cal/hr (1 lb = 454 g; 1 cal = 4.18 jou; 1 hp = 

 746 w; 1 jou/sec = 1 w). 



2-2: Values of the solubility of nitrogen and oxygen in water are 0.001 50 and 0.00332 

 g of gas at 1 atm/100 g water, respectively. Approximately how many cubic 

 centimeters of each gas are contained dissolved in the body fluids (200 lb, 80 per 

 cent water) under 1 atm of air (20 per cent oxygen, 80 per cent nitrogen)? 

 Neglect the fact that the solubility of gases is less in salt solutions than in pure 

 water. 



An anethetist may use a mixture up to 90 per cent oxygen, but he always re- 

 tains about 5 per cent C0 2 in the inhaled gas. Why? 



2-3: Assuming the total area of the adult human body to be 1 sq yd, calculate the 

 total force due to the atmosphere (pressure 14.7 lb/in. 2 ) on the body. In dynes; 

 in tons force. 



Calculate the total force on a skin diver at a depth of 450 ft. Why is he not 

 crushed? What precautions must he take while coming up to the surface? Why? 



2-4: Make two tables showing forces of repulsion — in dynes, of two like unit charges, 

 each with 3 x 10" 10 electrostatic units of charge — at distances 0.1, 1, 2, 5, 

 and 25 A apart; one table for a medium of air or a vacuum (dielectric con- 

 stant = 1), and the other for an aqueous solution (dielectric constant = 72). 

 Plot the numbers, force vs distance, for each case. 



