1. C Kitchens Physical Science E06
Measuring Motion:
Distance,
Displacement, Speed
and Velocity
C Kitchens
Physical Science E06
thecancermademedoit.com

2. Motion Motion is a change in position in a certain amount of time
To accurately describe motion, one must first consider the frame of reference
Frame of reference = a system of objects that are not moving with respect to one another

3. Motion
Relative Motion = an objects motion depends on the frame of reference…so it is relative to the frame of reference. For example, people moving in a car do not seem to be moving in reference to each other, but are moving at a definite speed in reference to people standing on a sidewalk.
You must choose a frame of reference that allows you to give a clear and relevant description of the motion.
schoolphysics.co.uk

4. Motion Distance is the length of a path between 2 points
The SI unit for distance is the meter (m). For longer distance, the kilometer (km) is often used. For smaller distances, you might see the centimeter(cm) or millimeter(mm).
googlesystem.blogspot.com

5. Motion
Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.
 Displacement is an example of a vector, which is a quantity that includes magnitude and direction.
Displacements in the same direction are added
Displacements in the opposite direction are subtracted.
en.wikipedia.org

6. Practice Problem
A cross country runner leaves school for a 10-mile run. They end their run at a Dairy Queen one mile from school. What is the total distance they ran? What is their displacement?

7. Practice Problem
An RV travels 45 km east and stays the night at a KOA. The next day it travels for 3 hours to the north, traveling 110 km. What is the displacement over the two days for the RV?

8. Motion
Displacement vectors that have different directions can be combined by graphing, with the vector that shows the sum of the displacements being called the resultant vector.
physicsclassroom.com

9. Practice Problem
If Vx = 6.8 units and Vy = 7.40 units, determine the magnitude of the displacement vector. Draw a diagram.

10. Motion
123rf.com
Speed is the rate at which an object moves, or the ratio between the distance and time of movement.
Speed = distance v = d
time t
The SI unit of speed is meters per second, m/s

11. Practice Speed
The Midnight Express heading west from Chicago to Albuquerque travels at 100 mph for 160 miles. How much time does this take?

12. Motion Constant speed is the speed that does not change.
A graph of constant speed is a straight line.
racebrakes.co.nz
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13. Motion
Average speed is the total distance divided be the total time. Average Speed is computed for the entire trip, and instantaneous speed is for a particular instant.
A graph of average speed is not a straight line. (flat line shows that the object is stopped)

14. Average Speed Problem #1
A student practicing for a track meet ran 250 meters (m) in 30 seconds (s). What was her average speed?

15. Average Speed Problem #2
Goliath chased a squirrel through the backyard. He followed the squirrel’s scent for 10 minutes and traveled 900 feet. He lost the scent and stood for 2 minutes while he tried to find it again.
Once he found the scent, he ran 300 feet in 1.75 minutes. What was Goliath’s average speed while he chased the squirrel?

16. Motion Velocity is speed in a given direction
ex. 10 m/s, west
Velocities in the same direction are added.
Velocities in opposite directions are subtracted.

17. Practice Velocity
An aircraft carrier traveled 4,727 kilometers east in
83 hours. What was the ship’s velocity in kilometers
per hour?

18. Motion
Velocities in 2 directions that are at angles can be used to calculate the resultant velocity by setting them up end to end and then solving for the 3rd vector. (a2 = b2 + c2)
A motorboat traveling 4 m/s, East encounters a current traveling 7.0 m/s, North. What is the resultant velocity of the motorboat?
If the width of the river is 80 meters wide, then how much time does it take the boat to travel shore to shore? What distance downstream does the boat reach the opposite shore?

19. Answer:
The resultant velocity can be found using the Pythagorean theorem. The resultant is the hypotenuse of a right triangle with sides of 4 m/s and 7 m/s.
It is [ (4 m/s)2 + (7 m/s)2 ] = 8.06 m/s
b. The time to cross the river is
t = d / v = (80 m) / (4 m/s) = 20 s
c. The distance traveled downstream is
d = v • t = (7 m/s) • (20 s) = 140 m