Linear Motion Lex I Corpus omne perseverare in

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 60 km/hr. It passes another car that travels southward at 60 km/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 = 10 m/s / 1 s = 10 m/s/s or 10 m/s 2

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/s 2 Which we round to 10 m/s 2 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. • • • 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 = 1/2 gt 2