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## Chapter 4

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**Physics:**Broad science dealing with the behavior and structure of matter and energy**Classical**Physics • Mechanics • Thermodynamics • Waves and Vibrations • Electromagnetism • Fluids/Materials**Modern Physics**• Relativity • Quantum (atomic) • Nuclear • Particle • Astrophysics**MECHANICS**The branch of Physics that studies the motions of objects and how that motion relates to physical concepts (such as mass and force).**All motion**depends on the viewpoint or the “Frame of Reference” of the observer.**MOTION: The changing of position in terms of a reference**point**Distance (d): How far something travels in changing**position (total) EX. I live 5 miles from NPHS. Where do I live? Scalar Quantity A quantity that has magnitude (size) only. No direction. Ex. Mass, time, temperature**DISPLACEMENT (∆ X orXf-Xi)**• Change in Position Final position related to initial position *REGARDLESS OF PATH EX. I live 5 miles from NPHS. Where do I live? EX. I live 5 miles WEST from NPHS. Where do I live? *∆X has both magnitude AND direction**VECTORS**Quantities that have both magnitude AND direction ∆X**DIRECTIONS for VECTORS**• Positive or negative • Up or down • North, South, East or West (NE, etc…) • Coordinates (graph points) • Map gridlines (F4) • Degrees (30◦ North or 30◦ North of East)**Distance is always a positive number, but displacement can**be positive OR negative. EX. Dude walks 5 meters west (-5 units). Dude walks 7 meters east (+7 units). Dude walks 4 meters east (+4 units). 6 meters East ∆X= ___________ ? d= __________ ? 16 meters**AVERAGE SPEED (v)**Def: The total distance traveled Time to travel distance s = d t • OR v = d t r = d t *SCALAR quantity**SI UNITS:**meters/second OR m/s *km/hr more common British Engineering Standard: feet/second OR ft/s *miles/hour (mph) more common *quick convert: mph ≈ twice m/s Conversion 1 m/s = 3.6 km/h = 2.24 mi/h 1 mph = 1.609 km/hr = 0.447 m/s**Usain Bolt holds the record for the 100m dash at 9.58**seconds. Find his average speed in : a.) m/s b.) km/hr c.) mph 100 m/9.58 sec = 10.44 m/s 10.44 m/s X (7.2 km/hr) = 37.58 km/hr ( 2 m/s ) 10.44 m/s X (4.5 mph) = 23.49 mph (2 m/s)**Instantaneous Speed**Speed at a specific instant in time**Average Velocity**How fast AND in what direction (Vector Quantity) Average Velocity = displacement/time**EX. The Green Racer drives 80 km west in 1 hour .**The Green Racer then drives 70 km east in 2 hours . Find the Green Racers average speed and average velocity. Speed=d/t……150 km / 3 hr ……… 50 km/hr. Velocity= ∆X /t…..10 km west /3 hr ….3.3 km/hr west…..OR …..-10 km/3hr….-3.3 km/hr