2Chapter: Motion and Momentum Table of Contents18Chapter: Motion and MomentumSection 1: What is Motion?Section 2: AccelerationSection 3: Momentum
3What is Motion?1Matter and MotionAll matter in the universe is constantly in motion, from the revolution of Earth around the Sun to elections moving around the nucleus of an atom.
4Changing Position 1 Something is in motion if it is changing position. What is Motion?1Changing PositionSomething is in motion if it is changing position.It could be a fast-moving airplane, a leaf swirling in the wind, or water tricking from a hose.When an object moves from one location to another, it is changing position.
5What is Motion?1Changing PositionThe runners sprint from the start line to the finish line.Their positions change, so they are in motion.
6What is Motion?1Relative MotionAn object changes position if it moves relative to a reference point.Picture yourself competing in a 100-m dash.You begin just behind the start line.When you pass the finish line, you are 100 m from start line.
7What is Motion?1Relative MotionIf the start line is your reference point, then your position has changed by 100 m relative to the start line, and motion has occurred.
8Distance and Displacement What is Motion?1Distance and DisplacementDisplacement includes the distance between the starting and ending points and the direction in which you travel.This figure shows the difference between distance and displacement.
9What is Motion?1SpeedSpeed is the distance traveled divided by the time taken to travel the distance.Speed can be calculated from this equation:
10What is Motion?1SpeedIn SI units, distance is measured in m and time is measured in s.As a result, the SI unit of speed is the m/s—the SI distance unit divided by the SI time unit.
11What is Motion?1Average SpeedAverage speed is found by dividing the total distance traveled by the time taken.An object in motion can change speeds many times as it speeds up or slows down.
12What is Motion?1Average SpeedThe speed of an object at one instant of time is the object's instantaneous speed.If it takes you 0.5 h to walk 2 km to the library, your average speed would be as follows:
13What is Motion?1Average SpeedAverage speed, instantaneous speed, and constant speed are illustrated here.
14You can represent the motion of an object with a distance-time graph. What is Motion?1Graphing MotionYou can represent the motion of an object with a distance-time graph.For this type of graph, time is plotted on the horizontal axis, and distance is plotted on the vertical axis.Click box to view movie.
15Distance-Time Graphs and Speed What is Motion?1Distance-Time Graphs and SpeedLook at the graph.According to the graph, after 1 s student A traveled 1 m.Student B, however, traveled only 0.5 m in the first second.
16Distance-Time Graphs and Speed What is Motion?1Distance-Time Graphs and SpeedSo student A traveled faster than student B.The line representing the motion of student A is steeper than the line for student B.
17Distance-Time Graphs and Speed What is Motion?1Distance-Time Graphs and SpeedA steeper line on the distance-time graph represents a greater speed.A horizontal line on the distance-time graph means that no change in position occurs.
18What is Motion?1VelocityIf you are hiking in the woods, you want to know not only your speed, but also the direction in which you are moving.
19This is why a compass and a map are useful to hikers. What is Motion?1VelocityThe velocity of an object is the speed of the object and direction of its motion.This is why a compass and a map are useful to hikers.
20What is Motion?1VelocityVelocity has the same units as speed, but it also includes the direction of motion.The velocity of an object can change if the object's speed changes, its direction of motion changes, or they both change.
21Section Check1Question 1To determine whether something has changed position, you need a _______.A. compassB. global positioning systemC. mapD. reference point
22Section Check1AnswerThe answer is D. If someone starts a car and drives it 100 meters from its parking spot, the parking spot can be used as a point of reference to show that the car moved.
23Section Check1Question 2Displacement includes your _______ and _______ as well as the _______ in which you have traveled.
24Section Check1AnswerIt includes your starting point, ending point, and direction in which you have traveled. It is possible to have traveled a great distance and still have a displacement of zero if you traveled in an enormous circle and ended right where you began.
25Question 3 1 Speed equals distance divided by _______. A. force Section Check1Question 3Speed equals distance divided by _______.A. forceB. massC. timeD. velocity
26Section Check1AnswerThe answer is C. The smaller the t value in s=d/t, the greater the speed.
27Acceleration and Motion 2Acceleration and MotionAcceleration is the change in velocity divided by the time it takes for the change to occur.Acceleration has a direction.If an object speeds up, the acceleration is in the direction that the object is moving.
28Acceleration and Motion 2Acceleration and MotionIf an object slows down, the acceleration is opposite to the direction that the object is moving.If the direction of the acceleration is at an angle to the direction of motion, the direction of motion will turn toward the direction of the acceleration.
29When the speed of an object increases, it is accelerating. Acceleration2Speeding UpWhen an object that is already in motion speeds up, it also is accelerating.When the speed of an object increases, it is accelerating.The toy car is accelerating to the right. Its speed is increasing.
30Acceleration2Slowing DownAcceleration occurs when an object slows down, as well as when it speeds up.The car is slowing down.During each time interval, the car travels a smaller distance, so its speed is decreasing.
31Motion is not always along a straight line. Acceleration2Changing DirectionMotion is not always along a straight line.If the acceleration is at an angle to the direction of motion, the object will turn.At the same time, it might speed up, slow down, or not change speed at all.
32Motion is not always along a straight line. Acceleration2Changing DirectionMotion is not always along a straight line.If the acceleration is at an angle to the direction of motion, the object will turn.At the same time, it might speed up, slow down, or not change speed at all.Click image to view movie.
33Calculating Acceleration 2Calculating AccelerationIf an object is moving in a straight line, its acceleration can be calculated using this equation.In SI units, acceleration has units of meters per second squared (m/s2).
34Positive and Negative Acceleration 2Positive and Negative AccelerationWhen you speed up, your final speed always will be greater than your initial speed.So subtracting your initial speed from your final speed gives a positive number.As a result, your acceleration is positive when you are speeding up.
35Positive and Negative Acceleration 2Positive and Negative AccelerationWhen your final speed is less than your initial speed, your acceleration is negative.Therefore, your acceleration is negative when you slow down.
36Graphing Accelerated Motion Acceleration2Graphing Accelerated MotionThe motion of an object that is accelerating can be shown with a graph.For this type of graph, speed is plotted on the vertical axis and time on the horizontal axis.
37Graphing Accelerated Motion Acceleration2Graphing Accelerated MotionAn object that is speeding up will have a line on a speed-time graph that slopes upward.An object that is slowing down will have a line on a speed-time graph that slopes downward.A horizontal line on the speed-time graph represents an acceleration of zero or constant speed.
38Section Check2Question 1A change in velocity divided by the time it takes for the change to occur equals the object’s _______.
39Section Check2AnswerThe answer is acceleration. Remember that, like velocity, acceleration has a direction. A car that takes a turn has changed its acceleration, even if nothing else changes.
40Section Check2Question 2Imagine yourself driving a car down an empty stretch of road. How many ways could you change your acceleration?
41Section Check2AnswerYou could step on the gas; you could also step on the brake; you could turn the wheel, or do any combination of these.
42Question 3 2 What is happening at point C in this speed-time graph? Section Check2Question 3What is happening at point C in this speed-time graph?
43A. the object is speeding up B. the object is slowing down Section Check2A. the object is speeding upB. the object is slowing downC. the object is at restD. the object is gone
44Section Check2AnswerThe answer is B. When the line falls, the object is slowing down.
45Momentum3Mass and InertiaThe mass of an object is the amount of matter in the object.In SI units, the unit for mass is the kilogram.The weight of an object is related to the object's mass.
46Momentum3Mass and InertiaObjects with more mass weigh more than objects with less mass.However, the size of an object is not the same as the mass of the object.
47Momentum3Mass and InertiaThe more mass an object has, the harder it is to start it moving, slow it down, speed it up, or turn it.This tendency of an object to resist a change in its motion is called inertia.Objects with more mass have more inertia.
48Momentum is usually symbolized by p. 3MomentumThe momentum of an object is a measure of how hard it is to stop the object, and it depends on the object's mass and velocity.Momentum is usually symbolized by p.
49Momentum3MomentumMass is measured in kilograms and velocity has units of meters per second, so momentum has units of kilograms multiplied by meters per second (kg . m/s).Momentum has a direction that is the same as the direction of the velocity.
50Conservation of Momentum 3Conservation of MomentumAccording to the law of conservation of momentum, the total momentum of objects that collide is the same before and after the collision.This is true for the collisions of billiard balls, as well as for collisions of atoms, cars, football players, or any other matter.
51Using Momentum Conservation 3Using Momentum ConservationThere are many ways that collisions can occur.Sometimes, the objects that collide will bounce off of each other.In other collisions, objects will stick to each other after the collisions.In both of these types of collisions, the law of conservation of momentum enables the speeds of the objects after the collisions to be calculated.
52Imagine being on skates when someone throws a backpack to you. Momentum3Sticking TogetherImagine being on skates when someone throws a backpack to you.Before the student on skates and the backpack collide, she is not moving.
54Supposed a 2-kg backpack is tossed at a speed of 5 m/s. Momentum3Sticking TogetherSupposed a 2-kg backpack is tossed at a speed of 5 m/s.Your mass is 48 kg, and initially you are at rest.Then the total initial momentum is
55You can use the equation for momentum to find the final velocity. 3Sticking TogetherAfter the collision, the total momentum remains the same, and only one object is moving.You can use the equation for momentum to find the final velocity.
56Colliding and Bouncing Off Momentum3Colliding and Bouncing OffSupposed two identical objects moving with the same speed collide head on and bounce off.Before the collision, the momentum of each object is the same, but in opposite direction.So the total momentum before the collision is zero.Click image to view movie.
57Colliding and Bouncing Off Momentum3Colliding and Bouncing OffIf momentum is conserved, the total momentum after the collision must be zero also.This means that the two objects must move in opposite directions with the same speed after the collision.
58Section Check3Question 1An object’s momentum can be increased either by increasing its _______ or its _______.
59Section Check3AnswerThe answer is mass or velocity. A thrown baseball is harder to stop than a thrown ping-pong ball. At the same time, a baseball thrown by a professional pitcher is harder to stop than the same baseball lobbed by a fan.
60Question 2 Answer 3 Explain the law of conservation of momentum. Section Check3Question 2Explain the law of conservation of momentum.AnswerThis law says that the total momentum of objects in collision is always the same after the collision as it was before the collision.
61Section Check3Question 3Two objects of the same mass are moving directly toward each other at the same speed. What is the total momentum of the two objects?AnswerThe total momentum is zero. This will be the same after the collision as well.
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