Speed Velocity and Acceleration.pptx

Science 7

1. Accelerated motion

2. Motion? Motion is an excellent topic to begin our study of physics. It is one of the most common phenomena. We see motion in the activities people do everyday: walking, jogging, running or riding a car to go to school or work. Motion can also be observed in the nature: clouds moving, raindrops falling, wind blowing the leaves of the tree and water moving in a never ending cycle. Our first step in the study of motion is to define concepts for motion in a straight light. Translation is the physical term for straight-line motion. We then extend our discussion to projectile motion.

3. Frame of Reference vs. Position The term position refers to the location of an object with respect to some reference frame. What is reference frame? Reference frame is a physical entity, such as ground, room, and building to which motion or position of an object is being referred When an object is undergoing a continuous change in position, we say that the object is moving. Motion is a relative term. It depends on the reference frame where motion is being observed.

4. Distance vs. Displacement A distinct has to be made between distance and displacement. A distance d refers to the actual length of path taken by an object in moving from its initial position to its final position. A displacement d refers to straight-line distance between its initial and final positions, with direction toward the final position. Distance is scalar, while displacement is vector

5. Problem 1: An object moves from point A to point B to point C, then back to point B and then to point C along the line shown in the figure below.  a) Find the distance covered by the moving object.  b) Find the magnitude and direction of the displacement of the object. 

6. Solution to Problem 1: a) distance = AB + BC + CB + BC = 5 + 4 + 4 + 4 = 17 km  b) The magnitude of the displacement is equal to the distance between the final point C and the initial point A = AC = 9 km  The direction of the displacement is the direction of the ray AB.

7. Problem 2: An object moves from point A to point C along the rectangle shown in the figure below.  a) Find the distance covered by the moving object.  b) Find the magnitude of the displacement of the object. 

8. Solution to Problem 2: a) distance = AB + BC = 5 + 3 = 8 km  b) Initial point is A and the final point is C, hence the magnitude of the displacement is equal the diagonal AC of the rectangle and is calculated using Pythagorean’s theorem as follows  AC 2  = AB 2  + BC 2  = 5 2  + 3 2  = 25 + 9 = 34  AC = √34 km = 5.83

9. Have you ever wondered why different objects travel the same distance but they take different amounts of time? This is because some objects are travelling faster or slower than others.

10. Speed vs. Velocity The term “ Speed ” and “ Velocity ” are used interchangeably in everyday situations. However, in physics they have distinct meanings. Speed is the distance that a body moves in a unit time and speed is a scalar quantity . When the speed of body is associated with a direction, the result is the velocity of the body. Velocity is a vector quantity . The speed of the body is the magnitude of its velocity. The SI unit for speed and velocity is meter per second, m/s

11. Speed vs. Velocity

12. Speed vs. Velocity

13. Speed vs. Velocity

14. Speed vs. Velocity

15. Speed Formula

16. Speed SI Unit

17. Let’s Solve This! Ian’s average speed was 4 m/s.

18. What is the instantaneous speed of Ian at 5s?

19. Take a look at the instantaneous speed of Ian below. What you can observe? They are always the same.

20. Speed vs. Velocity

21. Speed vs. Velocity

22. Speed vs. Velocity

23. Speed vs. Velocity

24. Speed vs. Velocity

25. Let’s Solve This! The runner’s average velocity is 8.33 m/s, East.

26. Speed vs. Velocity refers to the change of velocity in a particular instant

27. Speed vs. Velocity if the velocity is same throughout

28. Conversion of Units Complete the following table. 36 0.25 54 0.125 90

29. Formula: An object normally changes its speed while moving. Hence, it is necessary to distinguish between average speed and instantaneous speed. The average speed of a body is total distance it travelled divided by the time spent in travelling the total distance Average speed = Average speed = Average velocity = Average Velocity =  

30. Problem 1: A man walks 7 km in 2 hours and 2 km in 1 hour in the same direction.  a) What is the man's average speed for the whole journey?  b) What is the man's average velocity for the whole journey?

31. Solution to Problem 1 a) Average Speed= = = = 3km/ hr b) Average Velocity = = = = 3km/ hr  

32. Problem 2: How far can a bus travel in 4.5 hours if it travels along a straight highway at a speed of 40 km/hr?

33. The speed of the bus and the time are given. Write the working equation. Substitute the given values. Find the answer.

34. Activity: It’s Solving Time! Directions: Solve the following problems below involving speed and velocity. Show your solution. 1. A bird can fly a distance of 250 miles in 5 hours. What is the average speed of the bird ? 2. A cyclist drives along a straight highway for 25h with a displacement of 100 km south. What is the cyclist’s average velocity? 3. A jeepney moves along a straight road at an average speed of 10m/s. What is the distance travelled by the jeepney in 2.5 s?

35. Acceleration

36. Acceleration Since it has both magnitude and direction, it is a vector quantity. It can either be positive or negative according to the direction. The SI unit is given as m/s 2 . An object average acceleration over a period of time is its change in velocity ( ) divided by the duration of the time ( ) Mathematically. a = ( )  

37. Problem 1:   A car is moving from rest and attained a velocity of 80 m/s. Calculate the acceleration of the car after 5 s?

38. Solution to Problem 1: The equation to find out the acceleration is given by, a =  It is given that,  v f  = 80 m/s ,  v i  = 0 m/s , t = 5s a =  80m per s−0m per s/5s   = 16m/s 2  

39. Problem 2: Determine the acceleration of a coaster which moves with a velocity of 10 m/s, after 2s its velocity increases to 26 m/s.

40. Solution to Problem 1: The given parameters are Vf = 26m/s , Vi = 10 m/s , t = 2 s a =  a = 26−10/2 a = 8 m/s 2  

41. Solve Me! Directions: Analyze and solve the problem below. Show your solution in your Science activity notebook. A racehorse coming out from the gate accelerates from rest to a velocity of 15 m/s West in 3 seconds. What is its acceleration?

42. Directions: Copy and complete the table by solving the missing values of the quantities. Write your answers on your Science notebook.

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