Presentation on theme: "Free Write for 5 min: What is the difference between speed and velocity? Distance and Displacement? What is the difference between distance and displacement?"— Presentation transcript:
1Free Write for 5 min:What is the difference between speed and velocity? Distance and Displacement?What is the difference between distance and displacement?What does direction have to do with anything?
2Chapter 2 Kinematics in One Dimension Distance and Displacement
3KinematicsKinematics is the branch of mechanics that describes the motion of objects without necessarily discussing what causes the motion.Dynamics deals with the effect that forces have on motion.Together, kinematics and dynamics form the branch of physics known as Mechanics.
4How far have you gone if you run around the track one time?
5Distance vs Displacement Distance ( d )Total length of the path travelledMeasured in metersscalarDisplacement ( )Change in position (x) regardless of pathx = xf – xivector
7Chapter 2 Kinematics in One Dimension Speed and Velocity
8Average Speed SI units for speed: meters per second (m/s) The total distance traveled divided by the time required to cover the distance.SI units for speed: meters per second (m/s)
9Example 1: Distance Run by a Jogger How far does a jogger run in 1.5 hours (5400 s) if his average speed is 2.22 m/s?
10Average Velocity SI units for velocity: meters per second (m/s) The displacement divided by the elapsed time.SI units for velocity: meters per second (m/s)
11Example 2 The World’s Fastest Jet-Engine Car Andy Green in the car ThrustSSC set a world record of m/s in To establish such a record, the driver makes two runs through the course, one in each direction, to nullify wind effects. From the data, determine the average velocity for each run.
13What is the average velocity for both runs? (combined) What is the average speed for both runs? (combined)
14Instantaneous Velocity & Speed The instantaneous velocity indicates how fast the car moves and the direction of motion at each instant of time.The instantaneous speed is the magnitude of the instantaneous velocity
15Chapter 2 Kinematics in One Dimension Acceleration
16Describe the motion of the ball as it rolls down the ramp. What happens to the displacement and velocity as time goes by?Draw a Position vs time and Velocity vs Time graph of its motion
17What if anything changes when the ramp is facing in the opposite direction?
18AccelerationThe difference between the final and initial velocity divided by the elapsed timeSI units for acceleration: meters per second per second (m/s2)
19What does a negative acceleration mean? ScenarioAccelerationSpeeding up in the positive directionSlowing down in the positive directionSpeeding up in the negative directionSlowing down in the negative direction
22Question #5A ball is thrown toward a wall, bounces, and returns to the thrower with the same speed as it had before it bounced. Which one of the following statements correctly describes this situation?a) The ball was not accelerated during its contact with the wall because its speed remained constant.b) The instantaneous velocity of the ball from the time it left the thrower’s hand was constant.c) The only time that the ball had an acceleration was when the ball started from rest and left the hand of the thrower and again when the ball returned to the hand and was stopped.d) During this situation, the ball was never accelerated.e) The ball was accelerated during its contact with the wall because its direction changed.
23Question #6In an air race, two planes are traveling due east. Plane One has a larger acceleration than Plane Two has. Both accelerations are in the same direction. Which one of the following statements is true concerning this situation?a) In the same time interval, the change in the velocity of Plane Two is greater than that of Plane One.b) In the same time interval, the change in the velocity of Plane One is greater than that of Plane Two.c) Within the time interval, the velocity of Plane Two remains greater than that of Plane One.d) Within the time interval, the velocity of Plane One remains greater than that of Plane Two.e) Too little information is given to compare the velocities of the planes or how the velocities are changing.
24Question #7Two cars travel along a level highway. An observer notices that the distance between the cars is increasing. Which one of the following statements concerning this situation is necessarily true?a) Both cars could be accelerating at the same rate.b) The leading car has the greater acceleration.c) The trailing car has the smaller acceleration.d) The velocity of each car is increasing.e) At least one of the cars has a non-zero acceleration.
25Question #8The drawing shows the position of a rolling ball at one second intervals. Which one of the following phrases best describes the motion of this ball?a) constant positionb) constant velocityc) increasing velocityd) increasing acceleratione) decreasing velocity
26Question #9At one particular moment, a subway train is moving with a positive velocity and negative acceleration. Which of the following phrases best describes the motion of this train? Assume the front of the train is pointing in the positive x direction.a) The train is moving forward as it slows down.b) The train is moving in reverse as it slows down.c) The train is moving faster as it moves forward.d) The train is moving faster as it moves in reverse.e) There is no way to determine whether the train is moving forward or in reverse.
27Question #10Which of the following velocity vs. time graphs represents an object with a negative constant acceleration?
28Chapter 2 Kinematics in One Dimension Constant Acceleration Equations
29AP Kinematic Variables: a = accelerationt = time (elapsed)v = final velocity (at time t),vo = initial velocity (at time 0)x = position (at time t)xo = initial position (at time 0)
30Equations of Kinematics for Constant Acceleration AP Equation#1
31Equations of Kinematics for Constant Acceleration AP Equation#3
32Equations of Kinematics for Constant Acceleration If, a is constant:AP Equation#2
33Question #11Complete the following statement: For an object moving at constant, positive acceleration, the distance traveleda) increases for each second that the object moves.b) is the same regardless of the time that the object moves.c) is the same for each second that the object moves.d) cannot be determined, even if the elapsed time is known.e) decreases for each second that the object moves
34Example 8 An Accelerating Spacecraft A spacecraft is traveling with a velocity of m/s. Suddenly the retrorockets are fired, and the spacecraft begins to slow down with an acceleration whose magnitude is 10.0 m/s2. What is the velocity of the spacecraft when the displacement of the craft is +215 km, relative to the point where the retrorockets began firing?
37Question #12An object moves horizontally with a constant acceleration. At time t = 0 s, the object is at x = 0 m. For which of the following combinations of initial velocity and acceleration will the object be atx = 1.5 m at time t = 3 s?a) v0 = +2 m/s, a = +2 m/s2 b) v0 = 2 m/s, a = +2 m/s2c) v0 = +2 m/s, a = 2 m/s2 d) v0 = 2 m/s, a = 2 m/s2e) v0 = +1 m/s, a = 1 m/s2
38Question #13An airplane starts from rest at the end of a runway and accelerates at a constant rate. In the first second, the airplane travels 1.11 m. What is the speed of the airplane at the end of the second second?a) m/s b) m/sc) m/s d) m/se) m/sAns:D
39Question #14An airplane starts from rest at the end of a runway and accelerates at a constant rate. In the first second, the airplane travels 1.11 m. How much additional distance will the airplane travel during the second second of its motion?a) m b) mc) m d) me) mAnswer:c
40Chapter 2 Kinematics in One Dimension Section 6:Freely Falling Bodies
41Free FallIn the absence of air resistance, it is found that all bodiesat the same location above the Earth fall vertically withthe same acceleration. If the distance of the fall is smallcompared to the radius of the Earth, then the accelerationremains essentially constant throughout the descent.This idealized motion is called free-fall and the accelerationof a freely falling body is called the acceleration due togravity.
42Freefalling bodiesI could give a boring lecture on this and work through some examples, but I’d rather make it more real…
43Free fall problemsUse same kinematic equations just substitute g for aChoose +/- carefully to make problem as easy as possible
44h a v vo t Example 12 The referee tosses the coin up with an initial speed of 5.00m/s.In the absence if air resistance,how high does the coin go aboveits point of release?havvot?-9.80 m/s20 m/s+5.00 m/s
46Conceptual Example 14 Acceleration Versus Velocity There are three parts to the motion of the coin. On the wayup, the coin has a vector velocity that is directed upward andhas decreasing magnitude. At the top of its path, the coinmomentarily has zero velocity. On the way down, the coinhas downward-pointing velocity with an increasing magnitude.In the absence of air resistance, does the acceleration of thecoin, like the velocity, change from one part to another?
47Conceptual Example 15 Taking Advantage of Symmetry Does the pellet in part b strike the ground beneath the cliffwith a smaller, greater, or the same speed as the pelletin part a?
48Question #19 a) The two balls reach the ground at the same time. Two identical ping-pong balls are selected for a physics demonstration. A tiny hole is drilled in one of the balls; and the ball is filled with water. The hole is sealed so that no water can escape. The two balls are then dropped from rest at the exact same time from the roof of a building. Assuming there is no wind, which one of the following statements is true?a) The two balls reach the ground at the same time.b) The heavier ball reaches the ground a long time before the lighter ball.c) The heavier ball reaches the ground just before the lighter ball.d) The heavier ball has a much larger velocity when it strikes the ground than the light ball.e) The heavier ball has a slightly larger velocity when it strikes the ground than the light ball.
49Question #20 a) Both balls would follow trajectory 5. Two identical ping-pong balls are selected for a physics demonstration. A tiny hole is drilled in one of the balls; and the ball is filled with water. The hole is sealed so that no water can escape. Each ball is shot horizontally from a gun with an initial velocity v0 from the top of a building. The following drawing shows several trajectories numbered 1 through 5. Which of the following statements is true?a) Both balls would follow trajectory 5.b) Both balls would follow trajectory 3.c) The lighter ball would follow 4 and the heavier ball would follow 2.d) The lighter ball would follow 4 and the heavier ball would follow 3.e) The lighter ball would follow 4 or 3 and the heavier ball would follow 2 or 1, depending on the magnitude of v0.
50Question #21A cannon directed straight upward launches a ball with an initial speed v. The ball reaches a maximum height h in a time t. Then, the same cannon is used to launch a second ball straight upward at a speed 2v. In terms of h and t, what is the maximum height the second ball reaches and how long does it take to reach that height? Ignore any effects of air resistance.a) 2h, t b) 4h, 2tc) 2h, 4t d) 2h, 2te) h, t
51Chapter 2 Kinematics in One Dimension Section 7:Graphical Analysis of Velocity and Acceleration
52Calculus – the abridged addition Slope of the line(derivative)DisplacementVelocityaccelerationArea under the curve(integral)
57Question #22A dog is initially walking due east. He stops, noticing a cat behind him. He runs due west and stops when the cat disappears into some bushes. He starts walking due east again. Then, a motorcycle passes him and he runs due east after it. The dog gets tired and stops running. Which of the following graphs correctly represent the position versus time of the dog?
58Question #23The graph above represents the speed of a car traveling due east for a portion of its travel along a horizontal road. Which of the following statements concerning this graph is true?a) The car initially increases its speed, but then thespeed decreases at a constant rate until the car stops.b) The speed of the car is initially constant, but thenit has a variable positive acceleration before it stops.c) The car initially has a positive acceleration, but then it has a variable negative acceleration before it stops.d) The car initially has a positive acceleration, but then it has a variable positive acceleration before it stops.e) No information about the acceleration of the car can be determined from this graph.
59Question #24Consider the position versus time graph shown. Which curve on the graph best represents a constantly accelerating car?a) Ab) Bc) Cd) De) None of the curves represent a constantly accelerating car.
60Question #25Consider the position versus time graph shown. Which curve on the graph best represents a car that is initially moving in one direction and then reverses directions?a) Ab) Bc) Cd) De) None of the curves represent a car moving in one direction then reversing its direction.