Transcript Linear Motion

Linear Motion
• Lex I: Corpus omne perseverare in statu suo
quiescendi vel movendi uniformiter in directum,
nisi quatenus a viribus impressis cogitur statum
illum mutare.
• Every object in a state of uniform motion
tends to remain in that state of motion unless
an external force is applied to it.
Law of Inertia - Newton’s First Law
Some Definitions and Ideas
• Motion is relative – to something else!
• Speed – distance/time
• To go from my house to school takes me
30 minutes – it is 40 km
• What was my:
– Average speed
– Instantaneous speed
• To go from the Earth to the moon takes
about 3 days by Apollo capsule – what
was the average speed? (400,000 km)
• Do you think the average speed is
meaningful in this example?
• Velocity
• Vector and scalars
• Constant Velocity
• Changing Velocity Dv
• The speedometer of a car moving
northward reads 60km/hr. It passes
another car that travels southward at
60km/hr.
• Do both cars have the same speed?
• Do both cars have the same velocity?
• Changing Velocity Dv
• aka – Acceleration
• Acceleration = Change in Velocity/time
• Something is accelerating when it changes
it’s velocity!
Free Fall – Wheeee!
0 Seconds
0 m/s
1 second
10 m/s
2 seconds
20 m/s
3 seconds
30 m/s
Acceleration = Change in Velocity/time
= 10m/s / 1s
= 10m/s/s or 10m/s2
How Fast???
Instantaneous speed = acceleration x elapsed time
v = gt
Speed or Velocity = gravitational acceleration x time
Gravitational acceleration on Earth is 9.8 m/s2
Which we round to 10m/s2
If a rock falls for 10 seconds, how fast is it going when it
hits you???
How Far???
• Now you have to put the idea of average
velocity together with time and
acceleration.
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In the first second – how far did it fall?
Velocity to start? 0 m/s
Velocity at end of 1 second? 10 m/s
Average Velocity =
d=vt
=>>>
d = 1/2gt2