Motion
17
Transcript of Motion
Frames of ReferenceFrames of Reference
Object or point from which motion is Object or point from which motion is determineddetermined
Most common is the Most common is the
EarthEarth Motion is a changeMotion is a change
in in positionposition relativerelative to to
a frame of referencea frame of reference
What is motion?What is motion? If you are standing in one place, and your If you are standing in one place, and your
friend walks by you. friend walks by you. Are you moving relative to your friend?Are you moving relative to your friend? Is your friend moving relative to you?Is your friend moving relative to you? Are either of you moving relative to the Are either of you moving relative to the
earth?earth?
Answer:Answer:
You are moving relative to your You are moving relative to your friend, and your friend is moving friend, and your friend is moving relative to you!relative to you!
You are not moving relative to the You are not moving relative to the earth, but your friend is. You are both earth, but your friend is. You are both moving relative to the sun!moving relative to the sun!
What is motion?What is motion? If you and your friend are walking down the If you and your friend are walking down the
hall together at the same speed, in the same hall together at the same speed, in the same direction direction Are you moving relative to your friend?Are you moving relative to your friend? Is your friend moving relative to you?Is your friend moving relative to you? Are either of you moving relative to the Are either of you moving relative to the
Earth?Earth?
Answer:Answer: You are NOT moving relative to You are NOT moving relative to
your friend, and your friend is your friend, and your friend is NOT moving relative to you. You NOT moving relative to you. You both are moving relative to the both are moving relative to the earth.earth.
Explanation
Distance is the actual length measured of a particular path taken.
Displacement is the length and direction of a straight line drawn from the start to finish.
Evaluation
Distance vs. Displacement HO
1.5
Explanation
What’s your Vector? The most important distinction between “distance”
and “displacement” is that distance is a scalar and displacement is a vector.
Scalars are simple magnitudes. 15 apples 135 miles
Vectors contain information about the magnitude (size) and direction of a physical observable. 64 miles Southwest
Vectors are typically depicted as arrows drawn with a specific length and pointing in a specific direction.
your home
your school
A displacement has
Size = length of this arrow
displacement from home to school
displacement from home to school
2 Displacement and distance
To go to school from home...
size& direction.
Distance = length of path you travelled
( size of displacement)
l1l2l3
2 Displacement and distance
To go to school from home...your home
your school = l1 + l2 + l3
Elaboration
What’s your Vector? A car travels 6 miles East and then 8 miles North. Determine the distance traveled by the car. Draw and describe the displacement vector of the
car.
6 mi E
8 mi N10
mi
53o N of E
So the car’s displacement is 10 miles NE
Conclusion
Summary of Concepts Distance is the length of the path traveled. Displacement (from “dis”-place to “dat”-place)
is the length and direction of a line from start to finish.
Motion is a change in position relative to a point of reference.
Distance is a scalar quantity that contains only magnitude
Displacement is a vector quantity that contains both magnitude and direction.
total distance = ?
total displacement = ?
3km + 4km = 7 kmtotal distance
total displacement 3km north + 4km north= 7 km north
N
4 km
7 km north
3 km
Adding displacements
A car travels 4 km northA car travels 4 km norththen 3 km north.
4 Adding displacements
A car travels 4 km northA car travels 4 km norththen 3 km south.
4 km
1 km north
3 km
total distance = ?
total displacement = ?
= 3km + 4km = 7 kmtotal distance
total displacement = 3km south + 4km north
= 1 km north
N
a Graphical method
4 Adding displacements
A car travels 4 km northA car travels 4 km norththen 3 km east.
4 km
3 km
5 km
total distance = ?
total displacement = ?
= 3km + 4km = 7 kmtotal distance
total displacement
N
a Graphical method
d2= 32 + 42
d =5 km NE
‘tip’ of p joined to ‘tail’ of q
pq
p + q
Tip-to-tail method: Graphing
