Describing and Measuring Motion Chapter 1 Section 1

Examples of Motion Examples of motion are drifting, fluttering, flying, and chasing. There are simple motions and complicated motions. Motions may be over in a moment and motions may be continuous. Examples of motion are drifting, fluttering, flying, and chasing. There are simple motions and complicated motions. Motions may be over in a moment and motions may be continuous.

Recognizing Motion Deciding if an object is in motion isn’t as easy as it sounds. Think about this, as you read this, are you in motion? An object is in motion when its distance from another object is changing. Deciding if an object is in motion isn’t as easy as it sounds. Think about this, as you read this, are you in motion? An object is in motion when its distance from another object is changing.

Are you in Motion? Even if you are sitting still, you are in motion. You are actually moving about 30 kilometers every second. At that speed, you could travel from New York City to Los Angeles in about 2 minutes. Even if you are sitting still, you are in motion. You are actually moving about 30 kilometers every second. At that speed, you could travel from New York City to Los Angeles in about 2 minutes.

The Earth is in Constant Motion You are moving because you are on the planet Earth, which is orbiting the sun. Earth moves about 30 kilometers every second, so you and everything else on Earth are moving at that speed! You are moving because you are on the planet Earth, which is orbiting the sun. Earth moves about 30 kilometers every second, so you and everything else on Earth are moving at that speed!

Reference Point Whether an object is moving or not depends on your point of view. If you compare a book to the floor beneath it, they are not moving. If you compare them to the sun, the books are moving quite rapidly. Earth and the sun are different reference points! Whether an object is moving or not depends on your point of view. If you compare a book to the floor beneath it, they are not moving. If you compare them to the sun, the books are moving quite rapidly. Earth and the sun are different reference points!

Reference Point and Motion A reference point is a place or object used for comparison to determine if something is in motion. An object is in motion, if it changes position relative to a reference point. You must assume that the reference point is not moving. A reference point is a place or object used for comparison to determine if something is in motion. An object is in motion, if it changes position relative to a reference point. You must assume that the reference point is not moving.

Tricky Reference Point Have you ever been on a stopped school bus next to another school bus, and looked out the window? Suddenly, you think your bus is moving backward. When you look out the other window you realize that it was the other bus moving forward. Your bus seemed to be moving backward because you used the moving bus as your reference point. You assumed your reference point was stationary but it wasn’t. Have you ever been on a stopped school bus next to another school bus, and looked out the window? Suddenly, you think your bus is moving backward. When you look out the other window you realize that it was the other bus moving forward. Your bus seemed to be moving backward because you used the moving bus as your reference point. You assumed your reference point was stationary but it wasn’t.

Describing Distance To describe motion further, you need to use units of measurement. The system measurement is called the International System of Units or in French, Systeme International (SI) The SI unit for length is meter (m). To describe motion further, you need to use units of measurement. The system measurement is called the International System of Units or in French, Systeme International (SI) The SI unit for length is meter (m).

Meter A meter is little longer than a yard. To measure small objects, like the width of your fingernail, we use centimeters. The prefix centi means 1/100th. In order to measure even smaller objects such as a small black ant, we would use millimeters. Milli means 1/1000th. To measure long distances, scientists use kilometers. The prefix kilo means A meter is little longer than a yard. To measure small objects, like the width of your fingernail, we use centimeters. The prefix centi means 1/100th. In order to measure even smaller objects such as a small black ant, we would use millimeters. Milli means 1/1000th. To measure long distances, scientists use kilometers. The prefix kilo means 1000.

Calculating Speed Scientists use the SI unit to describe distance an object travels. A car might travel 90 kilometers per hour and an ant might travel 2 centimeters per second. If you know the distance an object travels in a certain amount of time, you know the speed of the object. Speed is the distance an object travels divided by the amount of time it takes to travel that distance. Speed = Distance Time Scientists use the SI unit to describe distance an object travels. A car might travel 90 kilometers per hour and an ant might travel 2 centimeters per second. If you know the distance an object travels in a certain amount of time, you know the speed of the object. Speed is the distance an object travels divided by the amount of time it takes to travel that distance. Speed = Distance Time

Constant Speed A ship traveling across the ocean may move at the same speed for several hours. A horse may canter across a field at a steady pace for several minutes. If so both the ship and horse, travel at a constant speed. If the speed of an object does not change, the object is traveling at a constant speed. A ship traveling across the ocean may move at the same speed for several hours. A horse may canter across a field at a steady pace for several minutes. If so both the ship and horse, travel at a constant speed. If the speed of an object does not change, the object is traveling at a constant speed.

Calculating Constant Speed If the horse travels at a constant speed of 21 meters for 3 seconds then you can calculate the horse’s speed per second. Speed = 21m = 7 m/s 3s If the horse travels at a constant speed of 21 meters for 3 seconds then you can calculate the horse’s speed per second. Speed = 21m = 7 m/s 3s

Average Speed Most objects do not move at a constant speed for very long. Look at page 21 Figure 5. The cyclists in the picture change their speed many times during the race. You can, however, find the average speed on the cyclists. Most objects do not move at a constant speed for very long. Look at page 21 Figure 5. The cyclists in the picture change their speed many times during the race. You can, however, find the average speed on the cyclists.

Calculating Average Speed To find average speed, you would divide the total distance traveled by the total time. For example: Suppose the cyclists travel 30 kilometers during the first 2 hours and 16 kilometers during the last hour. Add the total distance and divide by the total hours = 36 kilometers = 3 hours 36/3 = 12 kilometers/hour or 12 km/h To find average speed, you would divide the total distance traveled by the total time. For example: Suppose the cyclists travel 30 kilometers during the first 2 hours and 16 kilometers during the last hour. Add the total distance and divide by the total hours = 36 kilometers = 3 hours 36/3 = 12 kilometers/hour or 12 km/h

Describing Velocity Knowing and understanding velocity helps meteorologists predict storms. For example, if a weather forecaster announces that a severe storm is traveling 25 km/h, would you prepare for the storm? You must know where the storm is and which direction it is heading. Storms travel west to east so if you live east of the storm, you will need to take cover. Knowing and understanding velocity helps meteorologists predict storms. For example, if a weather forecaster announces that a severe storm is traveling 25 km/h, would you prepare for the storm? You must know where the storm is and which direction it is heading. Storms travel west to east so if you live east of the storm, you will need to take cover.

Velocity Velocity is speed in a given direction. You must know both the speed and direction of an object’s motion in order to know it’s velocity. The weather forecaster must state the storm’s velocity by saying it is traveling 25 km/h eastward. Air traffic controllers must also keep track of aircraft’s velocities because one error in speed or direction can cause a major collision. Velocity is speed in a given direction. You must know both the speed and direction of an object’s motion in order to know it’s velocity. The weather forecaster must state the storm’s velocity by saying it is traveling 25 km/h eastward. Air traffic controllers must also keep track of aircraft’s velocities because one error in speed or direction can cause a major collision.

Graphing Velocity To show the motion of an object, you would use a line graph. You would plot distance against time. The steeper the slope of the line, the faster the object is moving. Lets practice graphing the distance of two crawling babies. Open your textbook to page 25 and look at number 4. To show the motion of an object, you would use a line graph. You would plot distance against time. The steeper the slope of the line, the faster the object is moving. Lets practice graphing the distance of two crawling babies. Open your textbook to page 25 and look at number 4.