Motion

1. Motion

2. Unit 1: MotionChapter 1: Describing the Physical Universe • 1.1 The Science of Physics • 1.2 Distance, Time, and Measurement • 1.3 Speed

3. Key Question: How do we measure and describe time? 1.1 Investigation: Measuring Time Objectives: • Use electronic timing equipment and photogates. • Use units of time in calculations and conversions. • Correctly apply the terms accuracy, precision, and resolution to scientific instruments and measurements.

4. The Science of Physics • Physicsis a type of science that studies matter and energy. • Everything in the universe is believed to be either matter or energy.

5. The Science of Physics • Matter is anything that has mass and takes up space. • Energyis a measure of a system’s ability to change or create change in other systems.

7. The Science of Physics • A natural lawis a rule that describes an action or set of actions in the universe. • Sometimes a natural law, like Newton’s second law of motion, can be expressed by a mathematical equation. • We do not know all of the natural laws, so there is a lot left for students like you to discover!

8. Systems and variables • A variableis a factor that affects the behavior of the system. • When you are trying to find out how a system works, you look for relationships between the important variables of the system.

10. The scientific method • Learning by chance is one way to learn. • The scientific methodis a much more dependable way to learn and gather information. • Key parts include: • the hypothesis, a tentative, testable statement that tries to explain a set of scientific observations. • the experiment,a situation specifically set up to test or investigate a hypothesis.

11. The scientific method • 1. Scientists observe nature, then develop or revise hypotheses about how things work. • 2. The hypotheses are tested against evidence collected from observations and experiments. • 3. Any hypothesis that correctly accounts for all evidence from the observations and experiments is a potentially-correct theory. • 4. A theory is continually tested by collecting new and different evidence. Even one single piece of evidence that does not agree with a theory will force scientists to return to the first step.

13. Scientific theories • In science, the word theory is used differently than in everyday use. • A scientific theory is a comprehensive, well-tested description of how and why a process in nature works the way it does.

14. Scientific theories • The purpose of scientific research is to do experiments which show that existing theories do notgive the right prediction. • A theory that correctly explains 1,000 experiments but fails to explain the 1,001st cannot be wholly complete.

15. Scientific theories • It is important to be able to distinguish between pseudoscienceand science. • “The word pseudo means fake,” says professor Coker, of the Physics Department at the University of Texas. • Beware of “science” you find on the Internet. • Some of it is correct, but much of it is not.

16. Investigation systems • Experiments on systems usually have a question associated with them. • An example would be “How does the steepness of a ramp affect the speed of a ball?”

17. Investigation systems • The variable causing the change in the system is called the independent variable. • The angle of the ramp is the independent variable in this example.

18. Investigation systems • The variable that may show the effect of those changes is called the dependent variable. • The speed of the ball is the dependent variable.

19. Investigation systems • In an ideal experiment, you change only one variable at a time. • You keep all of the other variables the same. • A variable that is kept the same is called a control variable. What variables should be controlled in this system?

20. Scientific evidence • There are exacting rules defining what counts as scientific evidence. • Scientific evidence can include numbers, tables, graphs, words, pictures, sound recordings, or other information. • Scientific evidence must also beobjective and repeatable.

21. Models • In physics, a model links the variables in a system through cause-and-effect relationships. • Our car‑and‑track system links height and speed to the idea of energy. • This conceptual model is known as the law of conservation of energy, a natural law of physics.

22. Unit 1: MotionChapter 1: Describing the Physical Universe • 1.1 The Science of Physics • 1.2 Distance, Time, and Measurement • 1.3 Speed

23. Key Question: Can you predict the speed of the car as it moves down the track? 1.2 Investigation: Speed Objectives: • Predict what happens to a car’s speed as it travels down a track. • Create and interpret a speed vs. position graph. • Use a graph to make a prediction that can be quantitatively tested. • Calculate the percent error between a measurement and a prediction.

24. Measurement • A measurement is a precise value that tells how much. • A measurement communicates a quantity, and a unit. • For example, 2 meters is a measurement.

25. Distanceis the amount of separation between two unique points. Distance is measured in units of length. Commonly used units of length include: inches, miles, centimeters, meters, and kilometers. Distance

26. Two systems of measurement • The English Systemis used for everyday measurements in the United States. • During the 1800s, a new system of measurement—the Metric System—was developed in France and was quickly adopted. • In 1960, the Metric System was revised and simplified, and a new name was adopted—the International System of Units, or SI.

27. Two systems of measurement • Almost all fields of science worldwide use SI units because they are so much easier to work with. • In SI, factors of 10 are easier to calculate mathematically.

28. SI prefixes • Today, the United States is the only industrialized nation that has not switched completely to SI.

29. Measuring time • A quantity of time is called a time interval. • Most problems in physics measure time in seconds, so you may need to convert from hours or minutes.

30. Time scales in physics • The second(s) is the basic unit of time in both the SI and English systems. • In many experiments, you will observe how things change with time.

31. Accuracy, precision, and resolution • The words accuracyand precisionalsohave different meanings in science than every day use. • Accuracyis how close a measurement is to its accepted or “true” value. • Precisiondescribes how close together several repeated measurements or events are to one another.

32. Accuracy, precision, and resolution • Resolutionis another important term to understand when you are working with measured quantities. • Resolution is a reference to the smallest interval that can be measured.

33. Working with measurements • All measurements involve a degree of uncertainty. • It is impossibleto make a measurement of the exact true value of anything, except when counting. • Significant digitsare the meaningful digits in a measured quantity. • Mathematic answers involving measured quantities should have no more significant digits than the starting measurement with the least number of significant digits.

34. Unit 1: MotionChapter 1: Describing the Physical Universe • 1.1 The Science of Physics • 1.2 Distance, Time, and Measurement • 1.3 Speed

35. Key Questions: How do you design a valid experiment? 1.3 Investigation: Experiments and Variables Objectives: • Set up an experiment. • Explain the difference between control and experimental variables. • Discuss why conducting multiple experimental trials is better than gathering only one set of data.

36. Speed • To understand the concept of speed, use the bicycle example below:

37. Speed • Think about two questions: • How many meters does each bicycle move each second? • Does the bicycle move the same number of meters every second?

38. Speed • Think about two questions: • How many meters does each bicycle move each second? • Ans: Bike #1= 1 meter , Bike #2 = 3 meters • Does each bicycle move the same number of meters every second? • Ans: yes

39. Speed • The speedof a bicycle is the distance it travels divided by the time it takes. • At 1 m/s, bike #1 travels 1 meter per second. • At 3 m/s, bike #2 travels 3 meters per second. • Constant speed means the same distance is traveled every second. • Each bicycle is moving at constant speed, but their speeds are not the same.

40. Calculating speed • To calculate the speed of an object, you need to know two things: • the distance traveled by the object, and • the time it took to travel the distance.

41. Calculating speed • Speed is also a ratio of distance to time. • The word per means “for every” or “for each.” • You can also think of per as meaning “divided by.”

42. Relationships between variables • There are three ways to arrange the letters, or variables, that relate distance, time, and speed. • You can solve for any one of the three variables if you know the other two.

44. How to solve physics problems • Learning physics will make you a better problem solver, a skill is important in all careers. • The technique for solving problems in this book has four steps: • Identify what the problem is asking, and what variables need to be in the answer. • Identify the information you are given. • Identify any relationships between the information you are asked to find and what is given. • Combine the relationships with what you know and what you are to find.

45. Calculating speed An airplane flies 450 meters in 3 seconds. What is its speed in meters per second? • Looking for:… the speed in meters/second. • Given: …the distance (450 m) and the time (3 s) • Relationships:Use a version of the speed equation: v = d ÷ t • Solution:v = 450 m ÷ 3 s = 150 m/s

47. Serendipity is a term used to describe an event that happens by accident and results in an unexpected discovery. It is through education and a strong sense of curiosity, tempered with a bit of creativity (and yes, sometimes a little luck), that people can make great scientific discoveries. Scientific Method and Serendipity