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What can we measure?
We can measure mass, time, length, and temperature. What is the difference between a calculation and a measurement? What can we calculate? Area, Volume, Work, Pressure, Torque, Resistance, Energy, etc. What is included in a measurement? A measurement should always include 2 things: a number and a unit. What can be determined by knowing the unit(s)? In most cases, you can deduct what has been measured. Units are used to define measurements so that everyone knows exactly how much. Some examples of units are meter, foot, inch, centimeter or a mile. What are the 2 different systems of measurement? Customary (Sandard or English) and SI (Metric) Everything, whether it is a solid, liquid, or a gas has mass. It is a measure of how much of the substance is there - how many molecules. In the SI (metric) system, the units for mass are grams, kilograms (1000 grams) or milligrams (1/1000 grams). In the American unit (called the Customary (English) system), the weight of the substance is used, in pounds or ounces. A pound is 16 ounces. The easiest way to think of time is how long it takes something to happen. It may take 10 minutes to drive to school; it may take an hour to eat dinner. The units for time are the same around the world: seconds, hours, days, years. Length is a quality used to define an object. A pencil is 7 inches long. A student is 6 feet tall. A swimming pool is 2 meters deep. The most common units for the SI or metric system are a centimeter, a meter (100 centimeters) and a kilometer (1000 meters). In the Customary or English system, that most Americans use, common units are the inch, a foot (12 inches), or a mile (5280 feet). In addition to the length of an object, it is often useful to know the area or volume of the object in question. The area is how much room is on a surface like the floor of the classroom or the surface of a wing. Area is found by multiplying one length by another length. The result is called "square units". If a room is 20 feet by 25 feet long you would multiply 20ft X 25ft = 500 square feet (ft2). The volume of an object can either be how much space is available inside an object, like a fuel tank or how much actual material is inside a specific place. Volume has three measurements, length, height and width (all of these can be called lengths). Multiplying these together equal volume. The result is cubed. A 12 inch long section of a 2 inch by 4 inch board (2 in X 4 in X 12 in) would have a volume of 96 cubic inches (in3). Cubic feet, cubic meters, gallons, liters, and cubic centimeters (cc for short) are all common units for volume. The quality of temperature is a measure of how hot or cold something is. A thermometer is commonly used to determine the temperature of an object. The common units for temperature are degrees Fahrenheit or degrees Celsius (what used to be Centigrade). Temperature, in theory, is how quickly the molecules of a substance vibrates. If the molecules are vibrating rapidly, it results in a warm or hot temperature. If the molecules are vibrating slowly, they result in a cool or cold temperature. This is known as the Kinetic Molecular Theory. Pressure is measured as force per unit area (square inches, square meters). In metric units, pressure is measured in Newtons per square meter (N / m2). In the English system, pressure is usually measured in pounds per square inch. Example: The atmosphere (air) presses on your skin at 14.7 pounds per square inch (psi). Pressure can be powerful. A small pressure, spread over a very large area, can add up to be a very large force. Air pressure decreases as the altitude increases. This is what is known as an inverse proportion; pressure also decreases when the speed of the fluid (air, water) increases. This is Bernouli's principle.; When the temperature of a fluid increases, so does the pressure, if the volume stays the same. This is known as the Ideal Gas Law. Density is a measure of how much mass (the amount of molecules) is included in a given object or volume. Another way to think about it is how tightly the molecules are packed in a volume or object. Forces have been defined as pushes or pulls on an object. To determine the units of force, scientists and engineers use various mathematical formulas to measure force. An interesting point about the force is that in addition to a value and units, it also has a direction associated with it. In other countries, objects are measured in terms of their mass, in grams or kilograms. In the United States, however, people use the terms for weight to also mean mass. This works okay near the earth's surface because gravity is constant, so the units of "weight and mass" stay the same. Acceleration of gravity in the SI system of measurement is equal to 9.8 meters per second2, at sea level. Acceleration of gravity in the Standard system of measurement is equal to 32.174 feet per second2, at sea level. Scientists must be able to separate weight and mass. Therefore, the units are: kg of mass or Newtons of force. Mass will not change. Newtons will change with altitude. Acceleration of an object at high altitudes is less, due to gravity, therefore the weight (force from gravity) of the object is less. How fast an object moves is measured by its velocity. Velocity is calculated by dividing the distance traveled (a length) by the time it takes to travel the distance. The units of velocity are, for example, meters per second (m/s) or feet per minute (ft/min). If a person runs 15 kilometers in 2 hours, his or her velocity is 7.5 kilometers per hour (km/hr). If a car travels from Los Angeles, CA, to San Diego, CA , a distance of 120 miles, in 2 hours, its velocity is 60 miles per hour (120/2hrs=60 mph). One exception to these units is a term held over from sailing days, the knot. In aeronautics, the velocity of the air is often measured in knots. One knot is equal to about 1.7 feet per second (ft/s) or 1.15 miles per hour (mph). Acceleration is a measure of how the velocity of an object is changing over time. It can be found by computing the difference in velocities at first one time, then some time later, and dividing that by the difference in time. Newton’s First Law states that a body of mass in a state of rest tend to stay at rest and a body in motion tends to remain in motion, unless acted upon by another force. Newton’s Second Law states that an unbalance or force on a body tends to produce an acceleration in the direction of the force. Newton’s Third Law states that for every acting force there is an equal and opposite reacting force. |
Until recently, the meter is derived from what measurement?
Who developed the Fahrenheit scale and what was it derived from?
List 2 Calculations or Measurements that do not require units?
Describe the process by which sailors would measure boat speed in Knots?
