1. Describing Motion

2. Motion
An object is in motion if its distance from another object is changing.

3. Reference Point
A reference point is a place or object used for comparison to determine if something is in motion.
An object is in motion if it changes position relative to a reference point

4. How does the description of an object’s position depend on a reference point?
An object’s position is its in a certain
from a reference point.
distance
direction
Suppose your reference point changes…
The description of the position will
because the reference point is different, however the actual position
change at all.
change
will not

5. Relative Motion
Whether or not an object is in motion depends on the reference point.

6. To someone riding on a speeding train, others on the train don’t seem to be moving.

7. Practice Test Question

8. Practice Test Answer

9. How would you describe your position?
Distance and direction
North
Backward
South
East
Left
West Up
Forward
Right
Down

10. Practice Test Question

11. Practice Test Answer

12. Displacement Vs distance

13. Distance vs Displacement
The total length of the actual path from start to end.
Displacement -
Displacement is the length and direction of a straight line between starting and ending points.
When would distance and displacement be the same?
When an object moves in a straight line in one direction.

14. Distance and Displacement

16. Vector is a quantity that consists of both a magnitude and a direction.
Usually represented on a graphic by arrows
The length of the arrow represents magnitude
Direction of arrow indicates direction of vector
Must use vector addition to combine displacements

17. Combining Displacements
Add the magnitudes of two displacement vectors that have the same direction.
Two displacement vectors with opposite directions are subtracted from each other.

18. Combining displacements
Vector addition is the combining of vector magnitudes and directions
EX:
5km 10km
5 + 10= 15km
10km 3km
10 – 3= 7 km

19. Combining Displacements
Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.

20. Combining Displacements
Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.

21. Combining Displacements
Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.

22. Combining Displacements
Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.

23. Combining Displacements
Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.

24. Vector Displacement is a vector, but distance is not. Point B
Point A
Point A

25. Assessment Questions
A car is driving down the highway. From which frame of reference does it appear to not be moving?
standing at the side of the road
a car driving at the same speed but going the opposite direction
sitting inside the car
an airplane flying overhead

26. Assessment Questions
A car is driving down the highway. From which frame of reference does it appear to not be moving?
standing at the side of the road
a car driving at the same speed but going the opposite direction
sitting inside the car
an airplane flying overhead ANS: C

27. Assessment Questions
The metric unit of distance that would be most appropriate for measuring the distance between two cities is the
meter.
centimeter.
kilometer.
mile.

28. Assessment Questions
The metric unit of distance that would be most appropriate for measuring the distance between two cities is the
meter.
centimeter.
kilometer.
mile. ANS: C

29. If you walk across town, taking many turns, your displacement is the
Assessment Questions
If you walk across town, taking many turns, your displacement is the
total distance that you traveled.
distance and direction of a straight line from your starting point to your ending point.
distance in a straight line from your starting point to your ending point.
direction from your starting point to your ending point.

30. If you walk across town, taking many turns, your displacement is the
Assessment Questions
If you walk across town, taking many turns, your displacement is the
total distance that you traveled.
distance and direction of a straight line from your starting point to your ending point.
distance in a straight line from your starting point to your ending point.
direction from your starting point to your ending point. ANS: B

31. Assessment Questions
You travel 30 miles west of your home and then turn around and start going back home. After traveling 10 miles east, what is your displacement from your home?
20 km
20 km west
40 km
40 km west

32. Assessment Questions
You travel 30 miles west of your home and then turn around and start going back home. After traveling 10 miles east, what is your displacement from your home?
20 km
20 km west
40 km
40 km west ANS: B