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Transcript
Week Objective Student will: Study the effects of forces on objects though Newton’s First Law of Motion Law of Inertia Newton’s Second Law Newton’s Third Law Cornell Notes (1/3) Questions 1) What is Newton’s First Law Of Motion? Newton’s First Law of Motion Law of Inertia Inertia means “Tendency to resist change in motion” An object at rest, stays at rest. Object in motion, stays in motion unless acted upon by a force. Cornell Notes (2/3) 2) How do you know if an object is moving or not? Net Force (Resultant force): Sum up all the forces CPO Lab #0 Part II: Analyzing The Event CPO Lab #0 Part II: Analyzing The Event Cornell Notes (1/3) Questions 1) Newton’s 2nd Law is summarize with what formula? Newton’s 2nd Law: 𝐹𝑛𝑒𝑡 = 𝑚𝑎 Net Force = Mass x Acceleration Force is measured in Newton (N) Mass is measured in kilograms (kg) Acceleration is measured in (m/s2) Cornell Notes (2/3) 2) How does friction help move you forward when walking? 3) A bat hits a ball with a force of 50 N, what is the force of the ball on the bat? Newton’s 3rd Law: For every action force, there is a reaction force of equal magnitude (size), yet opposite in direction. Forces ALWAYS come in pairs Bat hits ball/ball hits bat Push on wall/wall pushes back Falling object pulled by Earth/Earth pulled by falling object Cornell Notes (3/3) Example 4) Is it possible to push someone harder than they push you? A 20 Kg girl and a 40 Kg boy are on ice. The girl pushes a boy with a force of 20 N. What force must the girl experience? Cornell Notes (1/5) Example: Newton’s Second Law The Human Torch is pulling the Thing (not an easy feat) straight up off the ground by applying a force of 3000 N. What is the magnitude of the Thing’s acceleration? Assume The Thing’s mass is 224 kg. Cornell Notes (2/5) Steps 1) Define Think of ALL the forces that act upon an object Given: m = 224 kg Fnet = 3000 N g = 9.8 m/s2 Unknown: 𝑎=? The Human Torch is pulling the Thing (not an easy feat) straight up off the ground by applying a force of 3000 N. What is the magnitude of the Thing’s acceleration? Assume The Thing’s mass is 224 kg. Cornell Notes (3/5) 2) Plan Choose an equation or situation: 𝐹𝑛𝑒𝑡 = 𝑚𝑎 𝐹𝑔 = 𝑚𝑔 Rearrange the equation to isolate the unknown: 𝐹𝑛𝑒𝑡 = 𝑚𝑎 𝐹𝑎𝑝𝑝 + −𝐹𝑔 =𝑎 𝑚 𝐹𝑛𝑒𝑡 𝑚𝑎 = 𝑚 𝑚 𝐹𝑎𝑝𝑝 + −𝑚𝑔 =𝑎 𝑚 𝐹𝑛𝑒𝑡 =𝑎 𝑚 𝐹𝑎𝑝𝑝 − 𝑚𝑔 =𝑎 𝑚 Cornell Notes (4/5) 3) Calculate Substitute the values into the equation and solve 𝐹𝑎𝑝𝑝 − 𝑚𝑔 =𝑎 𝑚 3000 − 224 ∙ 9.8 =𝑎 224 804.8 =𝑎 224 𝑎 = 3.592857143 𝑎 = 3.593 𝑚/𝑠 2 Cornell Notes (5/5) 4) Evaluate The Thing is accelerating 3.593 m/s2 upward. Cornell Notes (1/5) Example: Newton Second Law In order to travel, the Hulk has to leap from one place to another. Assuming his mass is 521.63 kg (1150 lbs), calculate the force that he exerts on the ground when he accelerates from 0 m/s to 391m/s (874.642 mph) in 0.8 seconds. Cornell Notes (2/5) Steps 1) Define Force needs magnitude and direction Given: m = 521.63 kg 𝑣𝑖 = 0 m/s 𝑣𝑓 = 391 m/s t = 0.8 seconds Unknown: F=? In order to travel, the Hulk has to leap from one place to another. Assuming his mass is 521.63 kg (1150 lbs), calculate the force that he exerts on the ground when he accelerates from 0 m/s to 391m/s (874.642 mph) in 0.8 seconds. Cornell Notes (3/5) 2) Plan Choose an equation or situation: aavg vf − vi = ∆t F = ma Rearrange the equation to isolate the unknown: aavg vf − v i = ∆t F = ma Cornell Notes (4/5) 3) Calculate Substitute the values into the equation and solve vf − vi aavg = ∆t 391 − 0 aavg = 0.8 aavg = 488.75 m/s 2 F = ma F = 521.63 ∙ 488.75 F = 254946.6625 F = 254946.663 N Cornell Notes (5/5) 4) Evaluate The Force is positive, indicating an upward direction, and is a very large number (after all, it is the Hulk). Through Newton’s Third Law of motion, the Hulk will need to exert a force of 291429.46 N to accelerate himself.