1. Motion

2. Some Motion Terms Distance & Displacement Velocity & Speed
Acceleration
Uniform motion
Scalar .vs. vector

3. Scalar versus Vector Scalar - magnitude only (e.g. volume, mass, time)
Vector - magnitude & direction (e.g. weight, velocity, acceleration)

4. Pictorial Representation
An arrow represents a vector
Length = magnitude of vector
Direction = direction of vector

5. Pictorial Representation
This arrow could represent a vector of magnitude 10 point to the “right”
This arrow could represent a vector of magnitude 5 point to the “left”

6. Distance & Displacement
Distance is the actual distance traveled.
Displacement depends only on Start & Finish line
Displacement is the distance traveled , in a certain direction.

7. Displacement Isn’t Distance
The displacement of an object is not the same as the distance it travels
Example: Throw a ball straight up and then catch it at the same point you released it
The distance is twice the height
The displacement is zero

8. Distance & Displacement

9. Distance & DisplacementB
4 m
5 m
3 m
You walk from A to B to C.
Your distance traveled is 7m
Your displacement form A is 5 m A

10. Velocity & Speed
Velocity is the displacement traveled in a certain time.
Speed is the distance traveled in a certain time.
Velocity is speed in a given direction.

11. Types of Speed
Instantaneous Speed is the speed at any specific instance
Average Speed is the total distance covered divided by total time

12. Speed
The average speed of an object is defined as the total distance traveled divided by the total time elapsed
Speed is a scalar quantity

13. Velocity
The average velocity of an object is defined as the total displacement traveled divided by the total time elapsed
Velocity is a vector quantity

14. Speed, cont
Average speed totally ignores any variations in the object’s actual motion during the trip
The total distance and the total time are all that is important
SI units are m/s

15. Velocity It takes time for an object to undergo a displacement
The average velocity is rate at which the displacement occurs
generally use a time interval, so let ti = 0

16. Velocity continued
Direction will be the same as the direction of the displacement (time interval is always positive)
+ or - is sufficient
Units of velocity are m/s (SI), cm/s (cgs) or ft/s (US Cust.)
Other units may be given in a problem, but generally will need to be converted to these

17. Speed vs. Velocity
Cars on both paths have the same average velocity since they had the same displacement in the same time interval
The car on the blue path will have a greater average speed since the distance it traveled is larger

18. Speed vs. Velocity You drive from Yakima to Seattle (140 miles away)
You stop in Ellensburg for a 2 hr lunch with a friend.
Your total driving time is 2 hours

19. Uniform Velocity Uniform velocity is constant velocity
The instantaneous velocities are always the same
All the instantaneous velocities will also equal the average velocity

20. Velocity Example

21. How fast is the plane moving in respect to the ground?
Velocity again
How fast is the plane moving in respect to the ground?

22. How fast is the plane moving in respect to the ground?
Velocity, yet again
How fast is the plane moving in respect to the ground?

23. How fast is the plane moving in respect to the ground?
Velocity (finally)
How fast is the plane moving in respect to the ground?

24. How fast is the plane moving in respect to the ground?
Velocity again (??)
How fast is the plane moving in respect to the ground?

25. How fast is the plane moving in respect to the ground?
Velocity - the last time
How fast is the plane moving in respect to the ground?

26. How fast is the plane moving in respect to the ground?
(Last) Velocity…
How fast is the plane moving in respect to the ground?

27. Acceleration
Change in velocity divided by the change in time

28. Acceleration
Changing velocity (non-uniform) means an acceleration is present
Acceleration is the rate of change of the velocity
Units are m/s2 (SI), cm/s2 (cgs), and ft/s2 (US Cust)

29. Average Acceleration Vector quantity
When the sign of the velocity and the acceleration are the same (either positive or negative), then the speed is increasing
When the sign of the velocity and the acceleration are in the opposite directions, the speed is decreasing

30. Instantaneous & Uniform Acceleration
The limit of the average acceleration as the time interval goes to zero
When the instantaneous accelerations are always the same, the acceleration will be uniform
The instantaneous accelerations will all be equal to the average acceleration

31. Relationship Between Acceleration & Velocity
Uniform velocity (shown by red arrows maintaining the same size)
Acceleration equals zero

32. Relationship Between Velocity & Acceleration
Velocity and acceleration are in the same direction
Acceleration is uniform (blue arrows maintain the same length)
Velocity is increasing (red arrows are getting longer)
Positive velocity and positive acceleration

33. Relationship Between Velocity & Acceleration
Acceleration and velocity are in opposite directions
Acceleration is uniform (blue arrows maintain the same length)
Velocity is decreasing (red arrows are getting shorter)
Velocity is positive and acceleration is negative

34. Kinematic Equations
Used in situations with uniform acceleration

35. Kinematic Equations - Ex #1
A car traveling with an initial velocity of 6 m/s, accelerates at 2 m/s2, for 6 seconds. What is the car’s final velocity?

36. Kinematic Equations - Ex #1 - Ans
A car traveling with an initial velocity of 6 m/s, accelerates at 2 m/s2, for 6 seconds. What is the car’s final velocity?

37. Galileo Galilei
Galileo formulated the laws that govern the motion of objects in free fall
Also looked at:
Inclined planes
Relative motion
Thermometers
Pendulum

38. Free Fall
All objects moving under the influence of gravity only are said to be in free fall
Free fall does not depend on the object’s original motion
All objects falling near the earth’s surface fall with a constant acceleration
The acceleration is called the acceleration due to gravity, and indicated by g

39. Acceleration due to Gravity
Symbolized by g
g = 9.81 m/s2
g is always directed downward
toward the center of the earth
Ignoring air resistance and assuming g doesn’t vary with altitude over short vertical distances, free fall is constantly accelerated motion

40. Free Fall – an object dropped
Initial velocity is zero
Let up be positive
Use the kinematic equations
Generally use y instead of x since vertical
Acceleration is g = m/s2
vo= 0
a = g

41. Free Fall – an object thrown downward
a = g = m/s2
Initial velocity ≠ 0
With upward being positive, initial velocity will be negative
vo 0
a = g

42. Free Fall - example
If a rock is dropped from a building, and it takes 18 seconds to reach the ground, how tall is the building?

43. Free Fall - answer
What do we know?

44. Free Fall - answer

45. Motion
The End