* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download constant velocity
Frame of reference wikipedia , lookup
Coriolis force wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Specific impulse wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Matter wave wikipedia , lookup
Fictitious force wikipedia , lookup
Classical mechanics wikipedia , lookup
Hunting oscillation wikipedia , lookup
Derivations of the Lorentz transformations wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Jerk (physics) wikipedia , lookup
Faster-than-light wikipedia , lookup
Equations of motion wikipedia , lookup
Velocity-addition formula wikipedia , lookup
Variable speed of light wikipedia , lookup
Classical central-force problem wikipedia , lookup
Newton's laws of motion wikipedia , lookup
PHYS 218: General Physics Summer 2013 Lecture 3: Analyzing motion and Newton’s Laws Read: Ch 2 Quick Review of Motion Position is the location of some object relative to a fixed point. Velocity is the slope of position vs. time. It tells you how position is changing. Acceleration is the slope of velocity vs. time. It tells you how velocity is changing. Quick Review of Motion Two Types of Motion “constant acceleration” => Net force x position (m) x position (m) “constant velocity” => No net force Time (sec) Time (sec) Quiz 1 position (m) Consider the following position vs. time graph: Time (sec) Which of these scenarios might this graph represent? A. B. C. D. E. A car starting from rest when a traffic light turns green. A car coming slowly to a stop when a traffic light turns red. A car moving at constant velocity. A car moving at constant acceleration. It cannot be a car. Quiz 2 velocity (m/s) Consider the following velocity vs. time graph: Time (sec) Which of these scenarios might this graph represent? A. B. C. D. E. A car starting from rest when a traffic light turns green. A car coming slowly to a stop when a traffic light turns red. A car moving at constant velocity. A car moving at constant acceleration. It cannot be a car. 50 miles Imagine a flight from the Great Smokey Mountains to West Lafayette. 50 miles 50 miles The change in position is called displacement. In this case 400 miles. 50 miles Question 3 Which type of motion, discussed last lecture, does a flight from the Great Smokey Mountains to Lafayette most resemble? A. Constant acceleration B. Constant velocity C. At rest Question 3 Which type of motion, discussed last lecture, does a flight from the Great Smokey Mountains to Lafayette most resemble? A. Constant acceleration B. Constant velocity C. At rest Takes off and accelerate briefly, fly for a few hours at constant velocity, and then decelerating briefly and land. Most of the time is spent flying at constant velocity. Question 3 Which type of motion, discussed last lecture, does a flight from the Great Smokey Mountains to Lafayette most resemble? B. Constant velocity Takes off and accelerate briefly, fly for a few hours at constant velocity, and then decelerating briefly and land. velocity (mph) 140 Time (hr) 3 Most of the time is spent flying at constant velocity. Question 4 Which graph could describe the position of the helicopter along the direction of travel as a function of time? B. A. 400 position (miles) position (miles) 400 Time (hr) 3 Time (hr) 3 Question 4 Which graph could describe the position of the helicopter along the direction of travel as a function of time? B. A. 400 position (miles) position (miles) 400 Time (hr) 3 Time (hr) 3 If you didn’t have a speedometer how could you estimate the speed of the helicopter from its position? position (miles) 400 Time (hr) 3.0 If you didn’t have a speedometer how could you estimate the speed of the helicopter from its position? displacement, Dx = 400 miles position (miles) 400 Time (hr) 3.0 total time, Dt = 3.0 hr If you didn’t have a speedometer how could you estimate the speed of the helicopter from its position? Average speed, |Vavg |= |Dx|/ Dt = 400 miles/3 hr = 130 mph displacement, Dx = 400 miles position (miles) 400 Average velocity, Time (hr) 3.0 total time, Dt = 3.0 hr Vavg = Dx/ Dt = 400 miles/3 hr = +130 mph direction If you didn’t have a speedometer how could you estimate the speed of the helicopter from its position? 400 position (miles) displacement, Dx = 400 miles Average speed, |Vavg |= |Dx|/ Dt = 400 miles/3 hr = 130 mph Time (hr) 3.0 total time, Dt = 3.0 hr Question 5 Is the speed you would read on the speedometer somewhere in the middle of the flight A. Bigger B. Smaller Than the average speed? 400 position (miles) displacement, Dx = 400 miles Average speed, |Vavg |= |Dx|/ Dt = 400 miles/3 hr = 130 mph Time (hr) 3.0 total time, Dt = 3.0 hr Question 5 Is the speed you would read on the speedometer somewhere in the middle of the flight A. Bigger B. Smaller Than the average speed? 400 position (miles) displacement, Dx = 400 miles Average speed, |Vavg |= |Dx|/ Dt = 400 miles/3 hr = 130 mph Time (hr) 3.0 total time, Dt = 3.0 hr Question 5 The speed read off the speedometer is the instantaneous speed, corresponding to one point in time. In the middle of the flight, this slope is bigger than the average speed. 400 position (miles) displacement, Dx = 400 miles Average speed, |Vavg |= |Dx|/ Dt = 400 miles/3 hr = 130 mph Time (hr) 3.0 total time, Dt = 3.0 hr Question Here’s the position and velocity of the helicopter: 400 velocity (mph) position (miles) 140 Time (hr) Time (hr) What would a graph of the acceleration look like? 3 Question Here’s the position and velocity of the helicopter: 400 velocity (mph) position (miles) 140 Time (hr) Time (hr) 3 What is the average acceleration? Where is the instantaneous acceleration large? Newton’s First Law If the total force acting on a body is zero, it will maintain its velocity* forever. *The object at rest is just a special case of this with velocity equal to zero. Quiz Consider a helicopter sitting at rest on the ground. The total force on the helicopter is: A. 0 B. downward C. upward Quiz Consider a helicopter hovering. The total force on the helicopter is: A. 0 B. downward C. upward Quiz Consider a helicopter gaining altitude at a constant rate. The total force on the helicopter is: v A. 0 B. downward C. upward Consider a helicopter cruising along at a constant 140 m.p.h. Using Newton’s First Law to help, identify all of the forces exerted on the helicopter. Newton’s Second Law The acceleration of an object is given by: FTotal a m with FTotal F Newton’s Second Law Let’s focus on FTotal a m Cart Demo For Next Time Read Chapter 3.1-3.3 (CHIP, iClickers, Books, etc.) FTotal a m Acceleration is proportional to force divided by mass: More force -> Greater acceleration FTotal a m Acceleration is proportional to force divided by mass: More mass -> Less acceleration Newton’s Second Law The acceleration on an object is given by: FTotal a m with FTotal F Newton’s Second Law FTotal F If multiple forces are present, calculate the total force as a vector sum. FTotal a m Forces add as vectors FTotal F FTotal a m Forces add as vectors FTotal F FTotal F y Fx F cos Fy F sin Fx F tan Fy Fy Fx F Fx2 Fy2 x Home at 11:45 a.m. Exit I-65 into Lafayette 11:30 a.m. What sort ofComplex quantities Motion will we use to describe position and distance? Got gas and breakfast around Lexington at 8:00 a.m. What information would you need to give in order for someone to retrace your steps? Pickup Interstate 75 5:45 a.am Left Smokey Mountains, 3:45 a.am 50 miles Home at 11:45 a.m. Exit I-65 into Lafayette 11:30 a.m. Complex Motion Got gas and breakfast around Lexington at 8:00 a.m. Pickup Interstate 75 5:45 a.am Left Smokey Mountains, 3:45 a.am 50 miles