Physics  What is physics? Measurements in physics - SI Standards (fundamental units) - Accuracy and Precision - Significant Figures - Uncertainties and Mistakes Language of physics - Mathematical Expressions and Validity

A way of describing the physical world  What is physics? A way of describing the physical world 6th Century B.C. in the Greek city of Miletus (now in Turkey) a group of men called “physikoi” tried to answer questions about the natural world. Physics comes from the Greek “physis” meaning “nature” and the Latin “physica” meaning natural things Physics is understanding the behavior and structure of matter - It deals with how and why matter and energy act as they do - Energy is the conceptual system for explaining how the universe works and accounting for changes in matter - The word energy comes from the Greek “en”, meaning “in” and “ergon”, meaning “work”. Energy is thus the power to do work. Sounds weird!! - Although energy is not a “thing” three ideas about energy are important It is changed from one form to another (transformed) by physical events It cannot be created nor destroyed (conservation) 3. When it is transformed some of it usually goes into heat

Areas within physics studied this year: Mechanics – Motion and its causes Thermodynamics – Heat and temperature Vibrations and Waves – Periodic motion Electromagnetism – Electricity, magnetism and EM waves Atomic – Structure of the atom, energy associated with atomic changes

 The Power of Physics Physics predicts how nature will behave in one situation based on the results of experimental data obtained in another situation. Mechanics → Newton’s Laws → Rocketry Electromagnetism → Maxwell’s Equations → Telecommunications

 What is physics? - Investigations in physics generally follow the scientific method Observations + initial data collection leading to a question, hypothesis formulation and testing, interpret results + revise hypothesis if necessary, state conclusions Some hypotheses can be tested by making observations. Others can be tested by building a model and relating it to real-life situations.

- Physics uses models to simplify a physical phenomenon They explain the most fundamental features of a phenomenon. Focus is usually on a single object and the things that immediately affect it. This is called the system Lord Kelvin, who lived in England in the 1800s, was famous for making models. To model his idea of how light moves through space, he put balls into a bowl of jelly and encouraged people to move the balls around with their hands. Kelvin’s work to explain the nature of temperature and heat still is used today.

Models help: identify relevant variables and a hypothesis worth testing guide experimental design (controlled experiment) make predictions for new situations Today, many scientists use computers to build models. NASA experiments involving space flight would not be practical without computers. An airplane simulator enables pilots to practice problem solving with various situations and conditions they might encounter when in the air. This model will react the way a plane does when it flies.

Measurements in physics Physics experiments involve the measurement of a variety of quantities. These measurements should be accurate and reproducible. The first step in ensuring accuracy and reproducibility is defining the units in which the measurements are made.

Measurements in physics - SI Standards (fundamental units) Fundamental units: distance – meter (m) time – second (s) mass - kilogram (kg) temperature - kelvin (K) current – ampere (A) luminous Intensity - candela (cd) Amount of substance – mole (mol) – 6.02 x 1023 Derived units: combinations of fundamental units speed (v) = distance/time acceleration (a) = velocity / time force (F) = mass x acceleration energy (E) = force x distance charge (Q) = current x time units: m/s units: m/s/s = m/s2 units: kgm/s2 = N (Newton) units: kgm2/s2 = Nm = J (Joule) units: As = C (Coulomb)

“It’s better to be roughly right than precisely wrong” Measurements in physics - Precision and Accuracy “It’s better to be roughly right than precisely wrong” – Allan Greenspan, U.S. Federal Reserve Chairman (retired)

Measurements in physics - Precision The precision of a series of measurements is an indication of the agreement among repetitive measurements. A “high precision” measurement expresses high confidence that the measurement lies within a narrow range of values. Precision depends on the instrument used to make the measurement. The precision of a measurement is one half the smallest division of the instrument for analogue and one least significant digit for digital. The precision of a measurement is effected by random errors that are not constant but cause data to be scattered around a mean value. We say that they occur as statistical deviations from a normalized value. Random variations can be caused by slight changes in pressure, room temperature, supply voltage, friction or pulling force over a distance. Human interpretation is also a source of random error such as how the instrument scale is read between divisions.

Measurements in physics - Significant Figures Significant figures reflect precision. Two students may have calculated the free-fall acceleration due to gravity as 9.625 ms-2 and 9.8 ms-2 respectively. The former is more precise – there are more significant figures – but the latter value is more accurate; it is closer to the correct answer. General Rules: 1. The leftmost non-zero digit is the most significant figure. 2. If there is no decimal point, the rightmost non-zero digit is the least significant. 3. If there is a decimal point, the rightmost digit is the least significant digit, even if it is a zero. All digits between the most significant digit and the least significant digit are significant figures.

Measurements in physics - Arithmetic with Significant Figures When adding or subtracting measured quantities the recorded answer cannot be more precise than the least precise measurement. Add: 24.686 m + 2.343 m + 3.21 m Answer: 30.24 m 3.21m has the least dp’s When multiplying or dividing measurements the factor with the least number of significant figures determines the recorded answer Answer: 6.8 cm2 2.1 cm has only 2sf Multiply: 3.22 cm x 2.1 cm Note significant digits are only considered when calculating with measurements; there is no uncertainty associated with counting. If you counted the time for ten back and forth swings of a pendulum and you wanted to find the time for one swing, the measured time has the uncertainty but the number of swings does not.

PRACTICE 3.6 s+9.89s+7.223s 5.674m-4.32m 9.0 kg x 2.0 kg 436 cm / 7 cm Use your understanding of precision to answer the following questions Use your notes on “What is Physics” to answer the following questions 3.6 s+9.89s+7.223s 5.674m-4.32m 9.0 kg x 2.0 kg 436 cm / 7 cm 1192.85754 kg / 55.23 kg 6. What are the three important ideas of energy? Why is energy conserved 7. Describe the purpose of a model 8. What language is the word Energy derived from? What does it mean? 9. How do we use models to design experiments 10. Define Physics