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 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 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 timeGravitational 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.

• 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