physics; all the rest is stamp · 2014. 9. 8. · 5 *Measuring & Describing motion* 30 km 20 km 15...
Transcript of physics; all the rest is stamp · 2014. 9. 8. · 5 *Measuring & Describing motion* 30 km 20 km 15...
“In science, there is only
physics; all the rest is stamp
collecting.” -Ernest Rutherford
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• Motion –occurs when something changes position
*Measuring & Describing motion* • Distance
–How far something has moved
Measured in: meters or kilometers
4 *Measuring & Describing motion*
Distance vs. Displacement
•Distance is how far an object has traveled
•Displacement is how far from the starting point an object actually moved
•Displacement does not equal distance traveled.
5 *Measuring & Describing motion*
30 km
20 km
15 km
15 km !
His Displacement is only 15 km.
6 *Measuring & Describing motion*
How fast Something Moves is SPEED
Speed is the distance an object travels in a certain period of
time.
7 *Measuring & Describing motion*
What is his rate of speed?
• Time= 30 min • What is his rate of speed? • Speed = distance/time • 1 km per min • 1 km/min
30 km
8 *Measuring & Describing motion*
Graphing Speed Constant Speed
9 *Measuring & Describing motion*
CONSTANT SPEED
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10 m/s
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S P E E D
What’s Happening Here? 12
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Velocity • In order to completely
describe the motion of an
object we need to include
not only the speed of the
object, but also
–the direction !
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If I told you that the moon man moved 40 km does that tell you where he is?
No.
You need to know the direction. 15
When describing velocity, you need to state the direction.
• Ex. 40 km/hr east
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Let’s Practice………… If a car travels
400m in 20
seconds , what
is its average
speed?
Practice ….#2
It takes Serina 0.25
hours to drive to
school. Her route is
16 km long. What is
Serina’s average
speed on her drive to
school?
…with a partner….
p.2..#s 1-8
Sometimes speed changes Changing Speed
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Acceleration • Changing Speed
–How fast the speed is changing. • Units: m/s2
–Velocity per sec –m/sec per sec
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• EX: If the acceleration is 10m/s2
•The object is increasing its speed by 10 m/s every sec.!
•How fast is it going after 5 sec.?
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•Acceleration: Changing Speed
•Covering more distance every second
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A cyclist
accelerates
from 0 m/s to
8 m/s in 3
seconds.
What is his
acceleration ?
Let’s Practice…………
A car advertisement
states that a certain
car can accelerate
from rest to 70 km/h
in 7 seconds. Find
the car’s average
acceleration.
10 m/s2
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Acceleration
•Can be positive or negative.
•Neg. Acc. Shows that the
object is slowing down.
•ACCELERATION IS IN THE
OPPOSITE DIRECTION FROM
THE VELOCITY!
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Cases of Acceleration 23
Changing Velocity
Constant Velocity
Which one’s which? 24
• During which of the following intervals are forces on the car balanced?
Hint: Balanced forces cause NO CHANGE in motion….
What is the child’s average speed for part A of her journey?
A
B
C
What’s Happening Here? 25
Instantaneous Speed 26
A. 7 km/hr B. 70 km/hr C. 300 km/hr D. 1750 km/hr
What is the average speed of a car that travels 350 kilometers in 5 hours?
EOCT QUESTIONS 27
1. Which graph(s) show(s) constant speed?
2. Which graph(s) show(s) acceleration?
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----- another
EOCT QUESTIONS
…with a partner….
p.2..#s 9-11 and
p.3..#s 12-16
THE END 29