Understanding Mechanics: Motion, Speed, and Velocity in Physics
This chapter explores the principles of mechanics, a fundamental branch of physics that examines the motion of objects and their relationships to physical concepts such as mass and force. It discusses essential concepts like motion, distance, displacement, and the importance of a reference frame. The chapter distinguishes between scalar quantities, such as speed, and vector quantities, like velocity, which consider direction. Further, it provides examples of average speed and velocity calculations, emphasizing units of measurement in both metric and imperial systems.
Understanding Mechanics: Motion, Speed, and Velocity in Physics
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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
