1. Motion
Motion
Motion

2. Section 2.1 – Describing Motion

3. Motion and Position
A reference point is needed to determine the position of an object.
Motion occurs when an object changes position relative to its reference point.
Motion depends on its point of reference.
Question – are you moving right now?

4. Distance and Displacement
Distance – how far an object has moved
Displacement – the distance and direction of an object’s change in position from the starting point
The SI unit for distance and displacement is the meter (m).

5. Distance and Displacement
Example: A runner runs from the start line 50 m north plus 30 m
in the opposite direction.
What is the distance?
What is the displacement?
50 m N
30 m S
START

6. Speed Speed – the distance an object travels per unit of time
Average speed – total distance traveled divided by the total
time of travel
Instantaneous speed – speed at a given point in time
Remember to use the metric system!
m/s (meters/second) or kilometers/hour
km/h

7. Velocity Velocity – includes the speed of an object and the direction
of its motion
Because velocity depends on direction as well as speed,
the velocity of an object can change even when its speed
does not!
Car is driving 30 km/hr
but it’s velocity is constantly
changing!

8. Equation to Find Speed
Speed (in meters per second) = distance (in meters) / time (in seconds)
s = d/t
Units – meters/second (m/s) or kilometers/hour (km/h)

9. Graphing Motion Motion can be shown on a distance vs. time graph
Time on x-axis
Distance on y-axis
On a distance vs. time graph the slope describes the speed
Steeper slope = faster speed
Horizontal line = zero speed = object at rest

10. Section 2.2 - Acceleration

11. What Is Acceleration? Acceleration is the rate of change of velocity.
When the velocity of an object changes, the object is accelerating.
A change in velocity can be either a change in how fast something is moving or a change in the direction it is moving.
So acceleration occurs when an object changes its speed, its direction, or both.

12. Speeding Up and Slowing Down
When you think of acceleration, you probably think of something speeding up. However, an object that is slowing down also is accelerating.
Acceleration also has direction, just as velocity does.

13. Speeding Up…
If the acceleration is in the same direction as the velocity, the speed increases and the acceleration is positive.

14. Slowing Down…
If the speed decreases, the acceleration is in the opposite direction from the velocity, and the acceleration is negative.

15. Changing Direction… Any time a moving object changes
direction, its velocity
changes and
it is accelerating.
The speed of
the horses in this
carousel is constant,
but the horses are
accelerating because their
direction is changing
constantly.

16. Calculating Acceleration
Vf = final velocity
Vi = initial velocity
t = time
Units = m/s2

17. Example with Positive Acceleration
Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.

18. Example with Positive Acceleration
The airliner is speeding up, so the final speed is greater than the initial speed and the acceleration is positive.

19. Example with Negative Acceleration
Imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 s.

20. Example with Negative Acceleration
The skateboarder is slowing down, so the final speed is less than the initial speed and the acceleration is negative.

21. Section 2.3 – Motion and Forces

22. Force Force – a push or pull
Sometimes it is obvious a force is being applied and
sometimes it is not
Forces cause the motion of an object to change
Forces are measured in Newtons (N)

23. Net Force
Net force – the sum of the forces acting upon an object

24. Balanced Forces
Balanced forces - occurs when the forces acting upon an
object are equal in size but opposite in direction

25. Unbalanced Forces
Unbalanced forces – when unequal forces act on the same
object; the object moves in the direction of the larger force

26. Inertia and Mass
Inertia - tendency of an object to resist any change in its motion
The greater the mass of an object, the greater its inertia.
Think about playing ping pong with a bowling bowl…
what’s the problem?
Newton’s First Law of Motion (aka Law of Inertia)
An object moving at a constant velocity keeps moving at
that velocity unless an unbalanced net force acts upon it.
How does this apply to a car crash?
Why can a seat belt prevent serious injury?