Conversion factors Thermodynamics

Pressure Pressure is equal to force divided by area The Si unit for force is a newton (N) A newton is equal to a kgm/s 2 (kilogram meter per second squared) Mass is not a unit of force However weight is a measure of force (it is equal to the force that gravity exerts on a mass)

Getting the weight of an object from its mass Assuming that the mass is located at or near the surface of the earth, multiply its mass in kilograms by the acceleration due to gravity at the earth’s surface (9.8 m/s 2 ) Example: What is the weight of a 50 kg mass at the surface of the earth?

correct This is an incorrect answer and would be marked completely wrong

A 100 kg mass rests on a table top that has dimensions of 30 cm by 40 cm. What is the average pressure exerted on the tabletop?

Force = mg = 980 N Area = 0.40m0.30m= 1.2 x m 2 (not.40 m x.30 m) A pascal (named after Blaise Pascal) is the SI unit for pressure and is equal to newton per square meter. Notice that when you write out a unit that is named after a famous scientist you use all lower case. However if you abbreviate the same unit with the first letter of the scientist’s name, you use upper case. newton or N

Liters to m 3 A liter is equal to a decimeter cubed (dm 3 ) So how do we convert 2500 liters to m 3 ?

Always show conversion factors with parentheses for each conversion factor when Converting squared or cubed quantities Converting mixed quantities When conversion requires more than simply moving a decimal place When you are not sure whether or not I am in a bad mood and want any excuse to mark your answer wrong

The tires on a car are at a pressure of 35 lb/in 2. What is this pressure in pascals? 2.2 lb = 1 kg 1 inch = 2.54 cm

Calories to joules 1 calorie = joules How many joules are there in 486 calories? The SI unit for energy is the joule (named after William Prescott Joule). The calorie comes from the Greek term caloric. The Greeks thought (and so did Europeans until the early 1800’s that heat (thermal energy) was a fluid.) Notice that by using scientific notation I can be very concise about the number of significant figures in my answer.