Transcript File - Physical Science
VELOCITY
Science Starter - Calculating Time Answers… 1.
How long would it take a cat walking north at 0.80 m/s to travel 12 m north? 2.
(15s) A car is driving forward at 15 m/s. How long would it take this car to pass through an intersection that is 11 m long? (0.73s)
Objective •
SWBAT calculate velocity given distance and time information
Agenda •
Science Starter
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Review Last Class
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Intro to New Material
What is speed?
Speed: how fast something is moving or how much distance is covered in a certain amount of time.
We will discuss two types of speed: (write) • Instantaneous speed: An object’s speed at any given instant.
• Average speed: An average of all instantaneous speeds.
Velocity •
Velocity is the same as speed, but it has a direction associated.
•
Speed has no specific direction.
Average Velocity (write)=
To calculate average speed •
average speed = total distance/time s = d/t
If you cover 75 m in 3 sec, how fast are you going?
Answer: 25 m/s If you travel 20 m/s for 10 m, how long did it take you?
Answer: .5 s
Video • https://www.khanacademy.or
g/science/physics/one dimensional motion/displacement velocity-time/v/calculating average-velocity-or-speed
Question • Can something have a constant speed but a changing velocity?
• Yes. All it has to do is turn.
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Remember: Velocity includes direction; speed does not.
Practice • A man walks 7 km East in 2 hours and then 2.5 km West in 1 hour. a) What is the man's average speed for the whole journey? b) What is the man's average velocity for the whole journey?
average speed = distance time = average velocity = displacement time = 7 km + 2.5 km 2 hours + 1 hour = 7 km - 2.5 km 2 hours + 1 hour = 9.5 km 3 hours = 3.2 km/h (approximate d to the nearest tenth) 4.5 km 3 hours = 1.5 km/h
Practice • You start walking from a point on a circular field of radius 0.5 km and 1 hour later you are at the same point. a) What is your average speed for the whole journey? b) What is your average velocity for the whole journey?
A. average speed = distance time = circumference time = 2 * 0.5 * Pi 1 hour = Pi km/h = 3.14 km/h (approxima ted) B. If you walk around a circular field and come back to the same point where you started the displacement, which a change in position, is equal to zero. Since the displacement is equal to zero, the average velocity is also equal to zero.
Converting between m/s and km/h • • • To convert from km/h to m/s: Change km to m: 1 km = 1000 m Change h to s: 1 h = 3600 s • Multiply by 1000 and divide by 3600 or • Divide the speed in km/h by 3.6 to obtain the speed in m/s.
For example, convert 75 km/h to m/s.
75 km 1h 1000m 1km 1h 3600s 21m/s
Converting between m/s and km/h Try the following unit conversion problems.
1.
Convert 95 km/h to m/s.
2.
A truck’s displacement is 45 km north after driving for 1.3 h. What was the truck’s average velocity in km/h and m/s?
3.
What is the displacement of an airplane flying 480 km/h [E] during a 5.0 min time interval?
Answers are on the next slide.
Converting between m/s and km/h Answers 1.
Convert 95 km/h to m/s.
(26m/s) 2. A truck’s displacement is 45 km north after driving for 1.3 h. What was the truck’s average velocity in km/h and m/s? (35 km/h [N], 9.6 m/s [N]) 3. What is the displacement of an airplane flying 480 km/h [E] during a 5.0 min time interval?
(40 km [E] or 40, 000 m [E])