1. TOPIC 2: MECHANICS
IB PHYSICS
GOHS

2. Kinematics The study of motion. Kinematics:
In kinematics, you are interested in the description of motion
Not concerned with the cause of the motion

3. Position A point in space
One dimensional, so generally on the x- or y-axis

4. Displacement Change in position
Symbol, in IB, is s but same as x or y
x (if horizontal) or y (if vertical)
Vector quantity
Units are meters (m) in SI

5. Displacements

6. Distance Distance may or may not be the magnitude of the displacement
Blue line shows the distance
Red line shows the displacement

7. 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

8. Average Velocity

9. Velocity continued
Direction of velocity is the same as the direction of the displacement
+ or - is sufficient
Time is always positive
Units, in IB, are ms-1 (m/s (SI))
Other units may be given in a problem, but generally will need to be converted

10. Speed Speed is a scalar quantity
same units as velocity
total distance / total time
May be, but is not necessarily, the magnitude of the velocity

11. Acceleration Changing velocity (non-uniform)
Acceleration: is the rate of change of the velocity
Units, in IB, are ms-2 (m/s² (SI))

12. Average Acceleration

13. 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

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

15. Relationship Between Velocity and 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)

16. Relationship Between Velocity and 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)

17. Kinematic Equations suvat equations: s distance/displacement (m)
u initial velocity (ms-1)
v final velocity (ms-1)
a acceleration (ms-2)
t time (s)

18. Kinematic Equations
Used in situations with uniform acceleration

19. Notes on the equations
Shows velocity as a function of acceleration and time

20. Notes on the equations
Gives displacement as a function of velocity and time

21. Notes on the equations
Gives displacement as a function of time, velocity and acceleration

22. Notes on the equations
Gives velocity as a function of acceleration and displacement

23. Free Fall
All objects moving under the influence of only gravity are said to be in free fall
All objects falling near the earth’s surface fall with a constant acceleration
Galileo originated our present ideas about free fall from his inclined planes
The acceleration is called the acceleration due to gravity, and indicated by g

24. Acceleration due to Gravity
Symbolized by g
g = 9.8 m/s²
g is always directed downward
toward the center of the earth

25. 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
u= 0
a = g

26. Free Fall -- an object thrown downward
a = g
Initial velocity  0
With upward being positive, initial velocity will be negative

27. Free Fall -- object thrown upward
Initial velocity is upward, so positive
The instantaneous velocity at the maximum height is zero
a = g everywhere in the motion
g is always downward, negative
v = 0

28. Thrown upward, cont. The motion may be symmetrical
then tup = tdown
then v = -u
The motion may not be symmetrical
Break the motion into various parts
generally up and down

29. Non-symmetrical Free Fall
Need to divide the motion into segments
Possibilities include
Upward and downward portions
The symmetrical portion back to the release point and then the non-symmetrical portion

30. Combination Motions

31. Problem-Solving Hints
Be sure all the units are consistent
Convert if necessary
Choose a coordinate system
Sketch the situation, labeling initial and final points, indicating a positive direction
Choose the appropriate kinematic equation
Check your results