PHYSICS

1. PHYSICS Units: Analyzing Motion Work and Energy Waves Electricity and Magnetism

2. TN Standards - Motion • CLE.3202.3.1: Investigate the relationships among speed, position, time, velocity, and acceleration • CLE.3202.Inq.2: Design and conduct scientific investigations to explore new phenomena, verify, previous results, test how well a theory predicts, and compare opposing theories • CLE.3202.Inq.4: Apply qualitative and quantitative measures to analyze data and draw conclusions that are free of bias • CLE.3202.Inq.6: Communicate and defend scientific findings

3. Chapter 11 - Motion • Sections: • 1 - Measuring Motion • 2 - Acceleration • 3 - Motion and Force

4. 1 - Measuring Motion • Key Questions: • How is a frame of reference used to describe motion? • What is the difference between speed and velocity? • What do you need to know to find the speed of an object? • How can you study speed by using graphs?

5. Frame of Reference • Observe an object in relation to other objects that stay in place, called reference points. • A frame of reference is used to describe the motion of an object relative to these reference points. • The trees in the background in Figure 1

6. Distance • Distance measures the path taken • To measure distance, you measure the length of the path that the object took. • Displacement measures only the difference between the final and starting positions

7. Speed & Velocity • Speed – how fast an object moved • Velocity – gives us both speed and direction • Velocity is described relative to a reference point • Up and right are positive; left and down are negative ( Cartesian Coordinate system ) +y -x +x -y

8. Motion • When an object changes position with respect to a frame of reference, the object is in motion • Velocity / Speed: Distance travelled in a certain time period D V/S t

9. Calculating Speed • Need two quantities – distance travelled & time • Average speed – distance divided by time interval • Instantaneous speed • speed at a given time • very small time interval • Speedometer in car D V/S t

10. Demonstration • Slope of a distance vs. time graph equals speed • Run a 6 m length ( in class? ) • Have your partner time you • What is your speed?

11. Graphing Motion • Sometimes easier to analyze motion on graphs

12. 2 - Acceleration • Key Questions: • What changes when an object accelerates? • How do you calculate the acceleration of an object moving in a straight line? • How can a graph be used to find acceleration?

13. Velocity Changes upon Acceleration • Speed can change, but so can direction • Notice speed is changing with each second

14. Changes in Direction • Uniform circular motion has centripetal acceleration • Sources: friction, tension • Demonstration

15. Circular Motion Demonstration • Foam ball with string attached to it • Swing ball with hand • Diagram features of motion • What happens when I let go of the string?

16. 2 - Acceleration • Key Questions: • What changes when an object accelerates? • How do you calculate the acceleration of an object moving in a straight line? • How can a graph be used to find acceleration?

17. BELLWORK • What changes when acceleration occurs?

18. 2 - Acceleration • Key Questions: • What changes when an object accelerates? • How do you calculate the acceleration of an object moving in a straight line? • How can a graph be used to find acceleration?

19. Calculating Acceleration V A t

20. Calculating Acceleration • Acceleration is the rate at which velocity changes • Acceleration is negative when slowing down

21. Graphing Accelerated Motion • The slope of a straight line on a speed vs. time graph is equal to the acceleration. • Constant Acceleration • Can also be seen from a distance vs. time graph

22. BELLWORK • How do we calculate average acceleration?

23. 3 - Motion and Forces • Key Questions: • What do scientists identify as the fundamental forces of nature? • What happens when there is a net force acting on an object? • What force always opposes motion? • Why is friction sometimes necessary?

24. Fundamental Forces • A Force is defined as any action that can change the state of motion of an object • Gravity, electromagnetic force, strong nuclear force, and the weak nuclear force • Fundamental forces vary in strength • Forces can act through contact or at a distance

25. Balanced and Unbalanced Forces • Whenever there is a net force acting on an object, the object accelerates in direction of the net force • Balanced forces do not change motion • Unbalanced forces do not cancel each other

26. Friction • Is a force • Always opposes motion • Static friction – occurs between stationary surfaces • Kinetic friction – occurs between moving surfaces • Sliding friction ( usually greater than rolling fiction ) • Rolling friction

27. Friction and Motion • Friction is necessary for many everyday tasks to function properly • Non-stick skillets • Cars would not move without friction!! • Can increase helpful friction or decrease unwanted friction • Sand on roads make them less slippery • Lubrication reduces friction

28. Friction and Balance of Forces • Cars do not or do move based on friction • Constant speed • Acceleration • No Slipping

29. Demonstration – Spring Scale • Drag wood and measure the force needed to overcome friction • Friction depends on force applied between surfaces • Rock keeps paper from being blown away by wind • More weight on block  more friction • Rougher surface  more friction