Ch. 3 & 4 Motion & Forces II. Describing Motion Motion Speed & Velocity Accelera
Nguyen, Trinh, Executive Producer has reference to this Academic Journal, PHwiki organized this Journal Ch. 3 & 4 Motion & Forces II. Describing Motion Motion Speed & Velocity Acceleration Newtons First Law Newtons First Law of Motion An object at rest will remain at rest in addition to an object in motion will continue moving at a constant velocity unless acted upon by a net as long as ce. motion constant velocity net as long as ce A. Motion Problem: Is your desk moving We need a reference point nonmoving point from which motion is measured
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A. Motion Motion Change in position in relation to a reference point. A. Motion Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move as long as ward. You have mistakenly set yourself as the reference point. B. Speed & Velocity Speed rate of motion distance traveled per unit time
B. Speed & Velocity Instantaneous Speed speed at a given instant Average Speed B. Speed & Velocity Problem: A storm is 10 km away in addition to is moving at a speed of 60 km/h. Should you be worried It depends on the storms direction! B. Speed & Velocity Velocity speed in a given direction can change even when the speed is constant!
C. Acceleration Acceleration the rate of change of velocity change in speed or direction a: acceleration vf: final velocity vi: initial velocity t: time C. Acceleration Positive acceleration speeding up Negative acceleration slowing down D. Calculations Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster GIVEN: d = 100 m t = 20 s v = WORK: v = d ÷ t v = (100 m) ÷ (20 s) v = 5 m/s You skate faster!
D. Calculations A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coasters acceleration GIVEN: vi = 10 m/s t = 3 s vf = 32 m/s a = WORK: a = (vf – vi) ÷ t a = (32m/s – 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s2 D. Calculations Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take as long as you to hear it GIVEN: v = 330 m/s d = 1km = 1000m t = WORK: t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s D. Calculations How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s2 GIVEN: t = vi = 30 m/s vf = 0 m/s a = -3 m/s2 WORK: t = (vf – vi) ÷ a t = (0m/s-30m/s)÷(-3m/s2) t = -30 m/s ÷ -3m/s2 t = 10 s
E. Graphing Motion slope = steeper slope = straight line = flat line = faster speed constant speed no motion speed E. Graphing Motion Who started out faster A (steeper slope) Who had a constant speed A Describe B from 10-20 min. B stopped moving Find their average speeds. A = (2400m) ÷ (30min) A = 80 m/min B = (1200m) ÷ (30min) B = 40 m/min E. Graphing Motion Acceleration is indicated by a curve on a Distance-Time graph. Changing slope = changing velocity
E. Graphing Motion slope = straight line = flat line = acceleration +ve = speeds up -ve = slows down constant accel. no accel. (constant velocity) E. Graphing Motion Specify the time period when the object was slowing down 5 to 10 seconds speeding up 0 to 3 seconds moving at a constant speed 3 to 5 seconds not moving 0 & 10 seconds
Nguyen, Trinh Executive Producer
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