Hence, for objects on or near the earth, the mass of the earth is very much greater than the object, and so the gravitational force between them makes objects fall towards the earth. That is why lead and feather fall at the same rate in a vacuum. It is also called Law of Inertia. This is the principle behind the recoil felt on pulling the trigger of a gun. The SI unit of electric charge, coulomb, is named after Charles Augustin de Coulomb who established the law. Why bursting of Balloon makes sound when pricked with a needle?

Hydraulic machines like the hydraulic press work on this principle. The SI unit of pressure is pascal which is named after Pascal who established this law. Doubling of the tension results in the doubling of the amount of stretch. Bernoulli's Principle It states that as the speed of a moving fluid, liquid or gas, increases, the pressure within the fluid decreases.

The aerodynamic lift on the wing of an aeroplane is also explained in part by this principle. Boyles's Law It states that temperature remaining constant, volume of a given mass of a gas varies inversely with the pressure of the gas. Kepler's Law Each planet revolves round the Sun in an elliptical orbit with the Sun at one focus. The straight line joining the Sun and the planet sweeps out equal areas in equal intervals.

The squares of the orbital periods of planets are proportional to the cubes of their mean distance from the Sun. Law of conservation of energy It states that energy can neither be created nor destroyed but it can be transformed from one form to another. Since energy cannot be created or destroyed, the amount of energy present in the universe is always remain constant. Tyndall effect The scattering of light by very small particles suspended in a gas or liquid. List of Main Branches of Physics. School Board.

Current Affairs. It is often necessary to convert from one type of unit to another. For example, if you are reading a European cookbook, some quantities may be expressed in units of liters and you need to convert them to cups. Or, perhaps you are reading walking directions from one location to another and you are interested in how many miles you will be walking. In this case, you will need to convert units of feet to miles. Let us consider a simple example of how to convert units. Let us say that we want to convert 80 meters m to kilometers km.

The first thing to do is to list the units that you have and the units that you want to convert to. In this case, we have units in meters and we want to convert to kilometers. Next, we need to determine a conversion factor relating meters to kilometers.

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A conversion factor is a ratio expressing how many of one unit are equal to another unit. For example, there are 12 inches in 1 foot, centimeters in 1 meter, 60 seconds in 1 minute, and so on. In this case, we know that there are 1, meters in 1 kilometer. Now we can set up our unit conversion.

We will write the units that we have and then multiply them by the conversion factor so that the units cancel out, as shown:. Note that the unwanted m unit cancels, leaving only the desired km unit. You can use this method to convert between any types of unit. Suppose that you drive the Note: Average speed is distance traveled divided by time of travel. First we calculate the average speed using the given units. Then we can get the average speed into the desired units by picking the correct conversion factor and multiplying by it. The correct conversion factor is the one that cancels the unwanted unit and leaves the desired unit in its place.

Average speed is distance traveled divided by time of travel. Take this definition as a given for now—average speed and other motion concepts will be covered in a later module. In equation form,. If you have written the unit conversion factor upside down, the units will not cancel properly in the equation. If you accidentally get the ratio upside down, then the units will not cancel; rather, they will give you the wrong units as follows:. Because each of the values given in the problem has three significant figures, the answer should also have three significant figures. The answer Note that the significant figures in the conversion factor are not relevant because an hour is defined to be 60 minutes, so the precision of the conversion factor is perfect.

Let us consider some information from the problem—if you travel 10 km in a third of an hour 20 min , you would travel three times that far in an hour. The answer does seem reasonable. There are several ways to convert the average speed into meters per second.

Two conversion factors are needed—one to convert hours to seconds, and another to convert kilometers to meters. If we had started with 0.

You may have noted that the answers in the worked example just covered were given to three digits. When do you need to be concerned about the number of digits in something you calculate? Why not write down all the digits your calculator produces? The module Accuracy, Precision, and Significant Figures will help you answer these questions.

While there are numerous types of units that we are all familiar with, there are others that are much more obscure. For example, a firkin is a unit of volume that was once used to measure beer. One firkin equals about 34 liters.

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Think about how the unit is defined and state its relationship to SI units. Some hummingbirds beat their wings more than 50 times per second. A scientist is measuring the time it takes for a hummingbird to beat its wings once. Which fundamental unit should the scientist use to describe the measurement? Which factor of 10 is the scientist likely to use to describe the motion precisely?

Identify the metric prefix that corresponds to this factor of One cubic centimeter is equal to one milliliter. What does this tell you about the different units in the SI metric system?

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The scientist will measure the time between each movement using the fundamental unit of seconds. Because the wings beat so fast, the scientist will probably need to measure in milliseconds, or 10 -3 seconds. The fundamental unit of length meter is probably used to create the derived unit of volume liter. The measure of a milliliter is dependent on the measure of a centimeter. Hint: Show the explicit steps involved in converting 1. American football is played on a yd-long field, excluding the end zones. How long is the field in meters? Assume that 1 meter equals 3.

Soccer fields vary in size. A large soccer field is m long and 85 m wide. What are its dimensions in feet and inches? What is the height in meters of a person who is 6 ft 1. Assume that 1 meter equals Mount Everest, at 29, feet, is the tallest mountain on the Earth.

What is its height in kilometers? Assume that 1 kilometer equals 3, feet. Suppose that one such plate has an average speed of 4. Then calculate the average speed of the Earth in its orbit in kilometers per second. Skip to main content. The Nature of Science and Physics. Search for:. Explain the most common prefixes in the SI units and be able to write them in scientific notation. The range of objects and phenomena studied in physics is immense. From the incredibly short lifetime of a nucleus to the age of the Earth, from the tiny sizes of sub-nuclear particles to the vast distance to the edges of the known universe, from the force exerted by a jumping flea to the force between Earth and the Sun, there are enough factors of 10 to challenge the imagination of even the most experienced scientist.

Giving numerical values for physical quantities and equations for physical principles allows us to understand nature much more deeply than does qualitative description alone. To comprehend these vast ranges, we must also have accepted units in which to express them. And we shall find that even in the potentially mundane discussion of meters, kilograms, and seconds a profound simplicity of nature appears—all physical quantities can be expressed as combinations of only four fundamental physical quantities: length, mass, time, and electric current.

Figure 2. Distances given in unknown units are maddeningly useless. Table 1. The Second. The Meter. The Kilogram. Metric Prefixes.

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