Physics chapter 1

1. Physics chapter 1 Section 2 Measurements in Experiments

2. OBJECTIVES • Students will be able to: • * List the basics SI units and the quantities they describe. • * Convert measurements into scientific Notation • * Distinguish between accuracy and precision • * use significant figures in measurements and calculations.

3. Numbers as measures Lets say I give you a 4. Can you give examples of how we can implement that four in math? Answers: we can add, subtract , multiply and divide that 4. We can also use it in an equation. We can use it in a fraction. There are more examples. How about physics and science can we use the 4 in the same way as in math. Answer: No, in physics an in science we can not have only a 4 or use it as it is because it leads to questions like what kind of quantity is being measured ? Like mass, distance, etc. What kind of units are used for measurement? And the 4 is usually accompany by a dimension.

4. Numbers as measure • The description of what kind of physical quantity is represented by a certain measurement is called dimension. • The three basic dimensions are: • * Length • * mass • * time • Some other can be expressed in terms of these three dimensions like force, velocity,energy,volume and acceleration.

5. Numbers as measure • The description of how much of a physical quantity is represented by a certain numerical measurement and by the unit with which the quantity is measured. • Although each dimension is unique, a dimension can be measured using different units. • For example, the dimensions of time can be measured in seconds, hours , or years.

6. SI is the standard measurement system for science • All systems of weights and measures, metric and non-metric, are linked through a network of international agreements supporting the International System of Units. The International System is called the SI, using the first two initials of its French name Système Internationald'Unités.

7. SI is the standard Measurement system for science • At the heart of the SI is a short list of base units defined in an absolute way without referring to any other units. The base units are consistent with the part of the metric system called the MKS system. In all there are seven SI base units: • the meter for distance, • the kilogram for mass, • the second for time, • the ampere for electric current, • the kelvin for temperature, • the mole for amount of substance, and • the candela for intensity of light.

8. SI is the standard measurement system for science • Other SI units, called SI derived units, are defined algebraically in terms of these fundamental units. • Derived Unitsare formed by combining the seven base units with multiplication or division. For example speed is usually expressed in units of meters per second(m/s). • Another example, the SI unit of force, the newton, is defined to be the force that accelerates a mass of one kilogram at the rate of one meter per second per second. This means the newton is equal to one kilogram meter per second squared, so the algebraic relationship is N = kg·m·s-2.

9. Converting into scientific notation • Physics is a science that often deals with big numbers like the distance between stars(100000000000000000)as well as small numbers like the distance between atoms in a solid (0.0000000001). • Because these numbers can be difficult to read and write, we usually like to expressed in powers of 10. These is called scientific notation . • For example the distance of the stars can be represented as and the distance of the atoms can be represented as .

10. Converting into scientific Notation • Lets see how the scientific notation works. • Lets take a number like 3000000 and converted to scientific notation. • Solution: • Lets take 3000000 and if want to convert it to scientific notation lets take a few steps • 1st step : we write 3000000 and put a decimal point at the end of the number 3000000. • 2nd step: we move the decimal point all the way up to the 3 3.000000. • 3rd step : we count how many spaces are in between those two points and if we are going to the left is positive and if we are going to the right is negative. • 4th step:

11. Converting to scientific notation • Example #1 • Convert .00008 to scientific notation • Solution: • Step 1: .00008. move the point to the end • Step 2: count the spaces between points 5 • Step 3: since you are going to the right is -5 • Step 4:

12. Student guided prACTICE • PROBLEMS 1-8 FROM SCIENTIFIC NOTATION WORKSHEET • GO OVER PROBLEMS 9-10 • PROBLEMS 11-16 FROM SCIENTIFC NOTATION WORKSHEET

13. Accuracy and Precision • Theories are based on observations and experiment, careful measurements are very important in physics. But no measurement is perfect. • So in order for us to describe the measurements we need to distinguished between: accuracy and precision. • What do you thing accuracy is ? * Accuracy: a description of how close a measurement is to the correct value . What do you thing precision is? Precision: is the degree of exactness of a measurement.

14. Accuracy and Precision • TYPES OF ERRORS IN EXPERIMENTS. • Experimental work is never free of errors, but its important to minimize error in order to obtain accurate results. • If some measurements are taken using one method and some are taken using a different method , a type of error called method error will result . • Another type of error is instrument error. If a meter stick or a balance is not working properly , this will introduce errors into any measurements made with the device.

15. Significant figures • What are significant figures? • Those digits in a measurement that are known with certainty plus the first digit that is uncertain. • Like 18.2