1. Motion
Chapter 2

2. Section 1: Describing Motion
What you will learn:
Distinguish between distance and displacement.
Explain the difference between speed and velocity
Interpret motion graphs.

3. Motion
Motion occurs when an object changes it’s position relative to a reference point.
A reference point is used to create a frame of reference, which is a coordinate system where the position of the object(s) is/are measured.

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

5. Speed Speed is the distance an object travels per unit of time.
Calculating Speed:
Any change over time is called a rate.
Speed = Distance (m)
Time (s)
Ex: Acura NSX
top speed:
168 mph

6. Solve This Speed Problem:
A car travels at a constant speed and covers a distance of 750m in 25s.
What is the car’s speed?
1. Write what you know:
d= 750m
t= 25s
2. The variable you need is speed
3. s= d/t
4. Use numbers: s= 750/25= 30m/s

7. More Speed Problems
1. An elevator travels from the first floor to the 60th floor, a distance of 210m, in 35s. What is the elevators speed?
s= d/t
s= 210/35 = 6m/s
2. How far does a car travel in 0.75h if it is moving at a constant speed of 88km/h?
d= st
d= 88km/h)(.75h) = 66km

8. Changing Speed
Average speed describes speed of motion when the speed is changing.
Average speed is the total distance traveled divided by the total time of travel.

9. Instantaneous Speed
Instantaneous speed is the speed at a given point in time.
In this example, the instantaneous speed is 100mi/h.
This person needs
to slow down!!!
Two examples of
motion in which the
instantaneous speed
changes are
acceleration and
deceleration.

10. Graphing Motion
The motion of an object over a period of time can be shown with a distance-time graph.
Time is plotted on the
x-axis and distance
on the y-axis.

11. Velocity
Velocity is a term that describes the speed of an object AND IT’S DIRECTION.
To tell if you are in danger of a hurricane you need
to know how fast
it is moving and in
what direction.

12. Velocity Continued…
If the cars in this picture maintain the same speed, does their velocity stay the same or change? Why?
Velocity changes because direction is constantly changing.

13. Did We Reach Our Learning Goals for Section One?
1. Distinguish between distance and displacement.
2. Explain the difference between speed and velocity.
3. Interpret this graph:

14. Section 2: Acceleration
What you will learn:
Identify how acceleration, time, and velocity are related.
Explain how positive and negative acceleration affect motion
Describe how to calculate the acceleration of an object.

15. Acceleration Review: Velocity is the change of position.
New: Acceleration is the change of velocity.
Velocity includes both the speed AND direction of an object.
A change in velocity can be a change in:
1. How fast something is moving OR
2. A change in the direction it is moving.
Recap: Acceleration occurs when an object changes it’s speed, it’s direction, or both!

16. Speeding Up and Slowing Down
Positive Acceleration is
when the speed of an object
is increasing.
Negative Acceleration is
is decreasing.

17. Let’s Do Some Practice
Is a car accelerating if it is moving in a straight line at a constant speed?
NO!
Is a car accelerating if it is moving in a straight line but slowing down?
YES!
Is a car accelerating if it is moving in a circular racetrack at a constant speed?

18. Changing Direction
Any time a moving object changes direction, it’s velocity changes and it is accelerating.

19. Calculating Acceleration
Acceleration is the rate of change in velocity.
To calculate the change in velocity:
Final velocity- initial velocity
To calculate acceleration (in m/s2)=
a = vf –vi t

20. Calculating Positive Acceleration
Example: An airplane starts at rest at the end of a runway and reaches a speed of 80m/s in 20s. Calculate acceleration.
a = vf –vi t
a = (80m/s – 0m/s) = 4m/s2
20s

21. Calculating Negative Acceleration
Example: A skateboarder is moving in a straight line at a constant speed of 3m/s and comes to a stop in 2 s. Calculate the acceleration:
a = vf –vi t
a = (0m/s -3m/s) = -1.5m/s2
2 s

22. Did We Reach Our Learning Goals For Section 2?
1. Identify how acceleration, time, and velocity are related.
2. Explain how positive and negative acceleration affect motion.
3. Describe how to calculate the acceleration of an object.

23. Section 3: Motion and Forces
What you will learn:
Explain how force and motion are related.
Describe what inertia is and how it is related to Newton’s first law of motion.
Identify the forces and motion that are present during a car crash.

24. What is a Force? A force is a push or pull.
Some forces are obvious, others aren’t as noticeable.
Example: the floor exerts a force on your feet, the atmosphere exerts a
force on your body, &
gravity pulls on you.

25. Changing Motion
When you exert a force on an object, the motion of the object may change.
When you hit a ball with a racket, the racket strikes the ball with a force that causes the ball to stop and then move in the opposite direciton.

26. Balanced Forces
Forces that are equal in size and opposite in direction are balanced forces.
Force does not always change velocity!

27. Unbalanced Forces Unbalanced forces are those that are not equal.
In the example below, the girl is pushing the box with a greater force than the boy so the box is going to move.

28. Inertia and Mass
Inertia is the tendency of an object to resist any change in its motion.
Example: What would be more difficult for you to stop with your hand…a tennis ball thrown at you or a bowling ball?

29. Speaking of Inertia…
Which of the following vehicles would you choose to more successfully slam into and break down a concrete wall? Why?

30. Newton’s First Law of Motion
“An object moving at a constant velocity keeps moving at that velocity unless an unbalanced net force acts on it. An object at rest will remain at rest unless an unbalanced force acts on it.”
Plain terms: An object is going to keep moving unless a force stops it, and an object that is not moving will stay still unless a force causes it to move.

31. How Does Newton’s Law Have Anything To Do With Me????
The “law of inertia” or Newton’s first law explains what happens in a car crash.
Which vehicle has the greater inertia?
Which vehicle has the greater damage?

32. You MUST Wear Your Seatbelt!!!
If a car traveling at 50km/h collides with something solid, the car crumples, slows down, and stops within 0.1 s.
Any passenger NOT
wearing a seatbelt
continues moving at
50km/h and within
0.02 s will collide with
the dash and windshield..

33. Why Seatbelts?
Seatbelts help to slow down a person as the car slows down and helps to prevent people from being thrown out of the car.
Statistic: Car safety experts say that about half the people in fatal car accidents would survive if they had worn seatbelts.

34. Did we reach our learning goals for section 3?
1. Explain how force and motion are related.
2. Describe what inertia is and how it is related to Newton’s first law of motion
3. Identify the forces and motion that are present during a car crash.