Understanding Motion and Displacement: A Guide to Describing and Calculating Motion

1. Chapter 11 Motion

2. Define motion • What is required to describe motion completely • How distance and displacement are different • How to calculate displacement 11.1 Concepts

3. Physicists study laws that govern space, time, forces, motion, matter and energy. • Motion (physics), any movement or change in position or time. • Motion is governed by four universal forces: • Gravitational forces • Electromagnetic forces • Strong nuclear forces • Weak nuclear forces • In order to describe motion, you must state the direction the object is moving as well as how fast the object is moving. • To describe motion accurately and completely, a frame of reference is necessary. Motion

4. The Frame of Reference determines how motion of an object is described. What is Frame of Reference

5. Measuring Distance • Distance is the length of a path between two points. • Distance is expressed in SI units of meters(m) Distance and Displacement

6. Measuring Displacement • To describe an objects position relative to a given point, you nee to know how far away and in what direction the object is from that point. • Displacement is the direction from the starting point and the length of a straight line from the starting to the ending point. • Displacements are sometimes used when giving directions. • They are examples of vectors. Distance and Displacement

7. Measuring Displacements To describe an object’s position relative to a given point, you need to know how far away and in what direction the object is from that point. Displacement provides this information.

8. Measuring Displacements Think about the motion of a roller coaster car. • The length of the path along which the car has traveled is distance. • Displacement is the direction from the starting point to the car and the length of the straight line between them. • After completing a trip around the track, the car’s displacement is zero.

9. Combining Displacements How do you add displacements? A vector is a quantity that has magnitude and direction. Add displacements using vector addition.

10. Combining Displacements Displacement is an example of a vector. • The magnitude can be size, length, or amount. • Arrows on a graph or map are used to represent vectors. The length of the arrow shows the magnitude of the vector. • Vector addition is the combining of vector magnitudes and directions.

11. Combining Displacements Displacement Along a Straight Line When two displacements, represented by two vectors, have the same direction, you can add their magnitudes. If two displacements are in opposite directions, the magnitudes subtract from each other.

12. Combining Displacements • Add the magnitudes of two displacement vectors that have the same direction. • Two displacement vectors with opposite directions are subtracted from each other.

13. Assessment Questions • If you walk across town, taking many turns, your displacement is the • total distance that you traveled. • distance and direction of a straight line from your starting point to your ending point. • distance in a straight line from your starting point to your ending point. • direction from your starting point to your ending point.

14. Assessment Questions • You travel 30 miles west of your home and then turn around and start going back home. After traveling 10 miles east, what is your displacement from your home? • 20 km • 20 km west • 40 km • 40 km west

15. Chanicedrives her scooter 7 kilometres north. She stops for lunch and then drives 5 kilometres east. What distance did she cover? What was her displacement? Practice 1

16. Anthony walks to the pizza place for lunch. He walk 1 km east, then 1 km south and then 1 km east again. What distance did he cover? What was his displacement? Practice 2

17. On his fishing trip Justin rides in a boat 12 km south. The fish aren’t biting so they go 4 km west. They then follow a school of fish 1 km north. What distance did they cover? What was their displacement? Practice 3

18. Tara goes on a camel safari in Africa. She travels 5 km north, then 3 km east and then 1 km north again. What distance did she cover? What was her displacement? Practice 4

19. Alex goes cruising on his dirt bike. He rides 700 m north, 300 m east, 400 m north, 600 m west, 1200 m south 300 m east and finally 100 m north. What distance did he cover? What was his displacement? (use 1cm = 100m) Practice 5

20. Jose buys a new moped. He travels 3 km south and then 4 km east. How far does he need to go to get back to where he started? Practice 6

21. What are two pieces of information required to accurately and completely describe motion? • What SI unit is used in association with distance? • A vector generally provides a direction and a ? • When 2 vectors are in the same direction, they are __ to find displacement. Let’s Review

22. Section Concepts • The students will be able to calculate speed and velocity using distance and displacement of vectors. 11.2Speed and Velocity

23. In physics, the word ratemeans the ratio of how much something changes divided by how long the change takes. What Is Speed?

24. To calculate the speed of an object, you need to know two things: • the distance traveled by the object • the time it took to travel the distance 3.1 Calculating speed

25. You are asked for speed in m/s. • You are given distance = 50 m; time = 7.5 s • Use v = d ÷ t • Plug in values and solve. v = 50 m ÷ 7.5 s ≈ 6.67 m/s • A bird is observed to fly 50 meters in 7.5 seconds. Calculate the speed of the bird in m/sec. Calculating speed in meters per second

29. Which Distance? • Farmer Jones drives 6 miles down a straight road. She turns around and drives 4 miles back. What was her average speed for this trip if it took 1 hour?

30. The velocity of an object tells you both its speed and its direction of motion. • A velocity can be positive or negative. • The positive or negative sign for velocity is based on the calculation of a change in position. Two cars going opposite directions have the same speed, but their velocities are different—one is positive and the other is negative. The velocity vector

31. Velocity appears to be very similar to speed, however, when describing the velocity of an object you need to provide a magnitude and a direction • Magnitude – the speed of the object • Direction – the direction the object is moving Velocity

32. Imagine two birds leave the same tree at the same time. The both fly at 10km/hr for 5 minutes. Why don’t they end up at the same place?

33. Velocity is the change in position divided by the change in time. The velocity vector

34. What Is Velocity?

37. Slope The slopeof a line is the ratio of the “rise” (vertical change) to the “run”(horizontal change) of the line.

38. Speed is the slope of the distance versus time graph

39. This distance versus time graph shows a boat traveling through a long canal. The boat has to stop at locks for changes in water level. • How many stops does it make? • What is the boat’s average speed for the whole trip? • What is the highest speed the boat reaches? Interpreting a distance versustime graph

40. The boat makes three stops because there are three horizontal sections on the graph. • The average speed is 10 km/h (100 km ÷ 10 h). • The highest speed is 20 km/h. The position changes by 20 km in one hour for the first, third, and fifth hours of the trip. Interpreting a distance versustime graph

41. When the direction of motion is part of the calculation, changes in position are referred to as displacement. Positive and negative velocities

42. 11.3Acceleration