MOTION An Introduction. Thoughts about Motion: A Short History.
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Transcript of MOTION An Introduction. Thoughts about Motion: A Short History.
![Page 1: MOTION An Introduction. Thoughts about Motion: A Short History.](https://reader036.fdocuments.in/reader036/viewer/2022081519/56649ede5503460f94beefb2/html5/thumbnails/1.jpg)
MOTION
An Introduction
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Thoughts about Motion:
A Short History
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Aristotle
• Greek philosopher • (384-322 BCE)
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Assumptions:
1.Natural laws could be understood by logical reasoning
2.Heavy objects fall faster than light objects
3.Moving objects must have forces exerted on them to keep them moving
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Galileo Galilei
• Italian (1564-1642)
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Assumptions:
1. Natural laws could be understood by experimentation
2. Objects of different weights fall at the same rate (except air resistance)
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Leaning Tower of Pisa
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Assumptions (continued)
3. Moving things, once moving, continue in motion without the application of forces
(ignoring friction)
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Sir Issac Newton
• English (1642 -1727)
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Sir Issac Newton
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Assumption:
Newton’s First Law : Inertia
Every object remains at rest or in motion (unless acted upon by an outside force)
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Motion : Speed
1. = how fast an object is moving2. speed = distance / time
Units = mi/hr, km/s, m/s, ft/sec, cm/s, in/s
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Motion : Speed
• Average speed =
total distance covered time interval
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Speed examples
1. It took me 12.8 hours to drive to Vegas. (914 miles)
What was my average speed?
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Speed Example 1
Av speed = total distance covered time interval
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Speed Example 1
= 914 mi = 71.4 mi / hr 12.8 hr
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Speed example 2
2. If I drive at an average speed of 79 mph ( mi / hr) ,
how many miles can I cover in 4.5 hours?
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Speed example 2
total distance = (av. speed) (time)
= (79 mi ) (4.5 hr) = (hr)
355.5 miles
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Speed example 3
3. How long will it take to drive to Chicago (1000 miles) if your average speed
is 63 mi/hr?
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Speed example 3
Time = distance = av. speed
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Speed example 3
(1000 mi) =(63 mi/hr)
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Speed example 3
15.9 hrs.
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SPEED IS RELATIVE
• Everything is moving• Earth is rotating (spinning)• Earth is orbiting around the sun• Galaxy is expanding
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SPEED IS RELATIVE
• Motion is measured relative to something1. e.g. Train relative to track 2. Space shuttle relative to
Earth 3. Other examples?
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SPEED IS RELATIVE
• How fast is the Earth is moving?
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SPEED IS RELATIVE
30 km/secRelative to the sun
• So… you are moving 30 km/sec• The desk is moving 30 km/sec
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VELOCITY
• = speed plus a DIRECTION
of motion
v = distance time
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VELOCITY Problem
• Two cars are driving in opposite directions.
• Car 1 is going 60 mi/hr.• Car 2 is also going 60 mi/hr.• Do both cars have the same
speed?
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VELOCITY Problem 1
• Yes
• Do both cars have the same velocity? Why or why not?
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VELOCITY Problem
• No.
• Because they are not traveling in the same direction.
• They have the same speeds, but opposite velocities.
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Acceleration
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Acceleration
• = (change in velocity)(change in time)
• = ∆v/ ∆ t
• = v2 – v 1
t2 – t 1
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Acceleration
• NOTE : Deceleration = negative acceleration• So, stepping on the brake =
− acceleration
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Acceleration Problem 1
• A 1965 T-bird with a 390 cubic inch engine can go from rest to 60 mi/hr in 8 seconds.
• What is its acceleration in m/sec2?
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Acceleration Problem 1
• What formula to use?
• How about the acceleration formula?
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Acceleration Problem 1
• Acceleration = ∆v/ ∆ t
• = v2 – v 1
t2 – t 1
• Right, but we need m/sec, not mi / hr, what to do?
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Acceleration Problem 1
SO, we need to convert….
(6x101 mi) (1km) (103 m) (1 hr) (hr) (6.2x 10-1 mi) (1 km) (3.6x103 s)
= 6 x 104 m = 2.6 x 102 m / s
2.23x 102s
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Acceleration Problem 1
• But, we need to know m/ s2
• (2.6 x 102 m/s) = 32.5 m/s2 (8 s)