DO NOW: (8/26/14)
• Convert the following units:
A) 540 cm  ________mm
B) 72,000 mL  _________L
C) 25 g  _________dag
• Write the following in scientific notation:
A) 54,000,000
WRITE DOWN HW:
B) 0.000837
Finish speed &
C) 0.000000000049
velocity problems
that we do not
complete in class
Data XT
•
•
•
•
Convert the following units:
250 mg = 0.250 g
476 L = 476,000 mL
20 m = 2000 cm
• Write the following in scientific notation.
• 873,000 8.73 x 10 5
• 270.056 2.70056 x 10 2
DO NOW: (8/24/14)
• Convert the following units:
A) 540 cm  5400 mm
B) 72,000 mL  72 L
C) 25 g  2.5 dag
• Write the following in scientific notation:
A) 54,000,000
5.4 x 107
B) 0.000837
8.37 x 10-4
C) 0.000000000049
4.9 x 10-11
OBJECTIVE for Week 3
SWBAT CALCULATE SPEED AND
VELOCITY.
Students will understand
relationships between force, mass
& motion.
Distance, Displacement, Speed, and Velocity
• The physics of motion is all about forces.
• Forces need to act upon an object to get it moving, or
to change its motion.
• Changes in motion won't just happen on their own.
• So how is all of this motion measured?
• Physicists use some basic terms when they look at
motion.
• How fast an object moves, its speed or Velocity, can be
influenced by forces.
(Note: Even though the terms 'speed' and 'velocity' are
often used at the same time, they actually have different
meanings.
Questions for Consideration
•
•
•
•
•
•
What is frame of reference?
What is distance?
How is displacement different from distance?
What is speed?
What is velocity?
What are scalar and vector quantities?
Frame of Reference
• Coordinate frame within which to measure position, motion,
or other properties of an object.
• OR...
• Observational frame tied to the motion of an observer.
Reference Frame
• Is the speed of the ball different relative to the
pitcher, the truck driver, and the jet pilot? Why
or why not?
Distance
• Distance (d) – how far an object travels.
• Does not depend on direction.
• Imagine an ant crawling along a ruler.
0
cm
1
2
3
4
• What distance did the ant travel?
• d = 3 cm
5
6
7
8
9
10
Distance
•Distance does not depend on direction.
•Here’s our intrepid ant explorer again.
0
cm
1
2
3
4
5
•Now what distance did the ant travel?
• d = 3 cm
•Does his direction change the answer?
6
7
8
9
10
Distance
•Distance does not depend on direction.
•Let’s follow the ant again.
0
cm
1
2
3
4
5
6
7
•What distance did the ant walk this time?
•d = 7 cm (Total Distance)
8
9
10
Displacement
• Displacement (D) – difference between an
object’s final position and its initial position.
• Does depend on direction.
• Displacement = final position – initial position
• In order to define displacement, we must include
direction!
Displacement vs. Distance
• Example of distance:
• The ant walked 3 cm.
• Example of displacement:
• The ant walked 3 cm EAST.
• An object’s distance traveled and its displacement aren’t
always the same!
Displacement
• Let’s revisit our ant, and this time we’ll find his displacement.
- +
0
cm
1
2
3
4
5
• Distance: 3 cm
• Displacement: +3 cm
• The positive gives the ant a direction!
6
7
8
9
10
Displacement
• Find the distance and displacement of the ant.
- +
0
cm
1
2
3
• Distance: 7 cm
• Displacement: +3 cm
4
5
6
7
8
9
10
Displacement vs. Distance
Jordan runs around a track that is 400 meters long three times, then
stops.
• What is the Jordan’s distance and displacement?
•Distance = 1200 m
•Displacement = 0 m
•Why?
Speed
•
•
•
•
Speed (s) – Rate at which an object is moving.
speed = distance / time
s = d/t
Like distance, speed does not depend on direction.
Speed
• A car drives 100 meters in 5 seconds.
1s
2
3
4
5
100 m
• What is the car’s average speed?
• s = d/t
• s = (100 m) / (5 s) = 20 m/s
Speed
•A rocket is traveling at 10 km/s. How long does it take
the rocket to travel 30 km?
Ways To Calculate Speed
•Constant speed is when you are
traveling at the same rate of
speed, such as 55 mph constantly
on a highway.
•Average speed is taking the total
distance traveled, and dividing by
the total time it takes. Used for
calculations that involve changing
speed.
•Instantaneous speed is the speed
at any one given point in time.
Average Speed
Bass Boat Speed
140
125
Distance (meters)
120
100
100
85
80
65
60
65
65
50
40
20
20
0
0
1
2
3
4
5
6
7
8
9
Time (seconds)
Average Speed = 125 meters = 15.6 m/s
8 seconds
10
Average
speed is
taking the
total distance
traveled (0 to
125 meters),
and dividing
by the total
time (1 to 9
seconds) it
takes.
Instantaneous Speed
Bass Boat Speed
140
125
Distance (meters)
120
100
100
85
80
65
60
65
65
50
40
20
20
0
0
1
2
3
4
5
6
7
8
9
10
Time (seconds)
Instantaneous Speed = 85 meters = 12.1 m/s
7 seconds
Instantaneous
speed is speed
at any given
point in time.
At 7 seconds,
the distance is
85 meters;
therefore the
IS is
Speed
• A racecar is traveling at 85.0 m/s. How far does the car travel
in 30.0 s?
Guided Practice
• A runner makes one lap around a 200 m track in a time of 25.0
s.
• What was the runner's average speed?
Guided Practice
• A runner makes one lap around a 200 m track in a time of 25.0
s.
• What was the runner's average speed? Answer: 8.0 m/s
Velocity
•Velocity is the speed of an object, but the direction is also included. It is
calculated the same as speed, but you must include a direction in your answer.
•Example: Cam Newton throws the football 40 mph toward the north field goal.
Velocity
• Velocity (v) – speed with direction.
• velocity = displacement / time
• v=D/t
Pulling It All Together
- +
1s
2
3
4
5
0
1
2
3
4
•cmBack to our ant explorer!
•
•
•
•
5
6
Distance traveled: 7 cm
Displacement: +3 cm
Average speed: (7 cm) / (5 s) = 1.4 cm/s
Average velocity: (+3 cm) / (5 s) = +0.6 cm/s
7
8
9
10
Guided Practice
• What is the average speed of a cheetah that sprints 100 m in 4
s?
• How about if it sprints 50 m in 2 s?
Guided Practice
• What is the average speed of a cheetah that sprints 100 m in 4
s?
100 meters / 4 seconds = 25 m/s
• How about if it sprints 50 m in 2 s?
50 meters / 2 seconds = 25 m/s
Same speed!
Velocity Problem
Indicate which of the following are velocities:
a.
b.
c.
d.
125 cm/sec
30 km/h northwest
350m/sec north
520 km/h
Quiz on Tues/Weds
• On Everything we have covered so far! Quiz will be at
beginning of class. If you are late – you must come after
school to make it up on Tutorial on Tuesday.
• Tutorial cancelled this THURSDAY 8/28!
SILENT & INDEPENDENT
• Speed & Velocity worksheet 1-8