what is physics? motion
TRANSCRIPT
Unit 1 - Constant Motion
Ms. Levine 1
September 2016
Motion
Part 1: Constant Speed
What is Physics?
Physics is the study of the physical world (energy and matter) and how they are
related.
Unit 1 - Constant Motion
Ms. Levine 2
September 2016
• What is the purpose of these motion maps?
• What is it showing us?
Connor runs quickly at a constant speed to the east. Madelyn runs slowly with a constant speed to the west. Draw a motion map for each below. (use the lines to help you)
Connor
Madelyn
Create your own motion map
What do you think about when you hear the word motion?
Unit 1 - Constant Motion
Ms. Levine 3
September 2016
In this unit, we will be discussing movement in a straight line.
What do we need to know to describe motion?
What do we need to know to describe motion?
• direction (left-right, forward-backward, north-south)
• units of measure
• a starting point (what happens if the starting point were to change?
Frame of Reference
- the place from which motion is observed and measured
Frame of Reference Video!.mp4
Frame of Reference #1.mp4
Let's watch a couple short videos to help us better understand this concept.
What is speed?
the distance traveled divided by the time it took to travel that distance
so to calculate speed we need distance and time
How far is a second?.mp4
SI Units
distance -
time -
speed -
Speed and Distance doesn't require us to define where we started from and where we ended up.
it just measures how far we traveled and how long it too to travel that far
Much of Physics is about knowing where something is and how its position changes with time
Unit 1 - Constant Motion
Ms. Levine 4
September 2016
Displacement
-x
+y
-y
+x
PennsylvaniaNew Jersey
For instance, if you drive 60 miles from Pennsylvania to New Jersey
and then traveled 20 miles back towards Pennsylvania,
How many miles did you travel?
How far are you from where you started? In what direction?
What is displacement?
Displacement - the change in position ( x)
- how far you are from where you started
Δx = Xf - Xo
Distance can only be a positive value since it is impossible to travel a negative distance.
xf xo-x
+y
-y
+xxo xf-x
+y
-y
+x
DisplacementHowever, displacement can be positive or negative since you can end up to the right or left of where you started.
Displacement is positive. Displacement is negative.
Vectors and Scalars
Scalar - a quantity that has only a magnitude (number or value)
Vector - a quantity that has both a magnitude and a direction
Quantity Vector Scalar
Time
Distance
Displacement
Speed
Which of the following are vectors? Scalars?
Ans
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1 How far your ending point is from your starting point is known as:
A distance
B displacement
C a positive integer
D a negative integer
2 A car travels 60m to the right and then 30m to the left. What distance has the car traveled?
+x- x
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Unit 1 - Constant Motion
Ms. Levine 5
September 20163 You travel 60m to the right and then 30m to the
left. What is the magnitude (and direction) of our diplacement?
+x- x
Ans
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4 Starting from the origin, a car travels 4km east and then 7 km west. What is the total distance traveled?
A 3 km
B -3 km
C 7 km
D 11 km
Ans
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5 Starting from the origin, a car travels 4km east and then 7 km west. What is the net displacement from the original point?
A 3 km west
B 3 km east
C 7 km west
D 11 km east
Ans
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6 You run around a 400m track. At the end of your run, what is the distance that you traveled?
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7 You run around a 400m track. At the end of your run, what is your displacement?
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Average Velocity
Speed is defined as the ratio of distance and time
Velocity is defined as the ratio of displacement and time
s = dt
ΔxΔtv = Average velocity = time elapsed
displacement
Average speed = distance traveledtime elapsed
Speeds are always positive, since speed is the ratio of distance and time; both of which are always positive.
But velocity can be positive or negative, since velocity is the ratio of displacement and time; and displacement can be negative or positive.
Unit 1 - Constant Motion
Ms. Levine 6
September 2016
8 Which of the following is a vector quantity?
A time
B velocity
C distance
D speed
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9 Average velocity is defined as change in ______ over a period of ______.
A distance, time
B distance, space
C displacement, time
D displacement, space
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10 You travel 60 meters to the right in 20 s; what is your average velocity?
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11 An elephant travels 60 meters to the left in 20 s; what is the average velocity?
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12 You travel 60 meters to the left in 20 s and then you travel 60 meters to the right in 30 s; what is your average velocity?
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13 You travel 60 meters to the left in 20 s and then you travel 60 meters to the right in 30 s; what is your average speed?
Ans
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Unit 1 - Constant Motion
Ms. Levine 7
September 2016
14 You run completely around a 400 m track in 80s. What was your average speed?
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15 You run completely around a 400 m track in 80s. What was your average velocity?
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16 You travel 160 meters in 60 s; what is your average speed?
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Let us transpose our motion maps to a position vs time graph.
Unit 1 - Constant Motion
Ms. Levine 8
September 2016
Now in reverse, a position vs time graph to a motion map.
Unit 1 - Constant Motion
Ms. Levine 9
September 2016
What does a position vs time graph look like of an object that is not moving? Moving at a constant velocity?
Draw below.
constant velocitymotionless