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 - Newtons 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 v

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 v aka – Acceleration Acceleration = Change in Velocity/time Something is accelerating when it changes its velocity!

Free Fall – Wheeee! 0 Seconds0 m/s 1 second10 m/s 2 seconds20 m/s 3 seconds30 m/s Acceleration = Change in Velocity/time = 10m/s / 1s = 10m/s/s or 10m/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 10m/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 = 1/2gt 2