Motion and Speed

 An object is in motion if it changes position relative to a reference point  Stationary objects make good reference points

 Whether or not an object is in motion depends on the reference point you choose.

 Distance is the total length of the actual path between two points. Displacement is the length and direction of a straight line between starting and ending points. What is the total distance this person traveled (in blocks)? 7 Blocks What is the total displacement of this person? 5 Blocks Northeast

 Quantities that have both a magnitude and a direction  Example: Displacement

 If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

 The speed of most moving objects is not constant

 Rate at which object is moving at a given instant in time

 Speed in a given direction  Velocity is a vector because it has both magnitude and direction  Changes in velocity may be due to changes is speed, changes in direction, or both

 You can use distance-versus-time graphs to interpret motion.

1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because it is not a stationary object. c. Yes, because it is very large. d. Yes, because it can travel very far.

1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because it is not a stationary object. c. Yes, because it is very large. d. Yes, because it can travel very far.

2.To describe a friend’s position with respect to you, you need to know a. Your friend’s distance from you. b. The direction your friend is facing. c. Your friend’s distance and direction from you. d. Your friend’s distance from a nearby object.

2.To describe a friend’s position with respect to you, you need to know a. Your friend’s distance from you. b. The direction your friend is facing. c. Your friend’s distance and direction from you. d. Your friend’s distance from a nearby object.

3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster a. moves farther in the same amount of time. b. has more mass. c. has the louder engine. d. has less momentum.

3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster a. moves farther in the same amount of time. b. has more mass. c. has the louder engine. d. has less momentum.

4. To describe an object’s motion, you need to know its a. position. b. change in position. c. distance. d. change in position over time.

4. To describe an object’s motion, you need to know its a. position. b. change in position. c. distance. d. change in position over time.