Energy and Motion

Essential Question: How is energy conserved?

-How do you calculate speed?

- How do you describe velocity?

- How do you graph motion?

8.4Speed and Velocity

Vocabulary 8.4

1.Speed--The distance an object travels per unit of time.

2.Average Speed--The overall rate of speed at which an object moves

1. Speed= Distance (total distance an object travels )

Time (total time)

1.instantaneous speed-- The speed of an object at one instant of time.

2.Velocity– Latin word = velox meaning “swift” Speed in a given direction.

3.Slope-- The steepness of a graph line; the ratio of the vertical change

(the rise) to the horizontal change (the run).

Slope= Rise

Run

Calculate Speed pg. 307The speed of an object is the distance the object moves per

unit of time.

How would you describe the motion of an airplane??• we can say it moves fast!!

How about the motion of a snail?• The motion would be reallllllllllllllllllllly slow!! (pg. 307 last P.)

• Speed is a type of rate. (rate tells you the amount of something that occurs or changes in specific time)

To calculate the speed of an object divide the distance the object travels by the amount of time it takes to travel that

distance.

Distance

Speed equation: Speed= Time

SI units for speed pg. 307

The SI unit for speed is meters per second= m/s *The slash / is read as “per”

Plane= travels at a constant speed of 260 m/s=

Explain what this means to you….This means that a plane travels a distance of 260 meters per 1 sec.

Space shuttle reaches a speed of 28,000 kph

1.Are these SI units?

2.How far does the shuttle travel in one hour at that speed?

Pearson Interactive Activity

Pearson Interactive Activity

Instantaneous Speed pg. 308, 309

Average Speed--The overall rate of speed at which an object moves (r.

• To calculate the average speed (The overall rate of

speed at which an object moves)of an object, divide the total distance traveled by the total time.

Average speed equation:Speed= Distance (total distance an object travels)

Time (total time)

Instantaneous speed is the speed at which an object is moving at a given instant in time.

• A moving object’s speed may change.

The SI unit for speed is m/s, or meters per second.

Use the data from all three legs to solve for each triathlete’s average speed.

CLUE (average Speed= Distance (total distance)

Time (total time)

Figure 1--Speed and Velocity pg. 308

How Do You Describe Velocity? Pg. 310

When describing an object’s motion,

you need to know both its speed

and its direction.Example: Thunderstorm speed 25 km/h

Is it imp. To know in which direction is traveling????

When you know both the speed and direction of an object’s motion, you know the velocity of the object.

• Speed in a given direction is

velocity.

How Do You Graph Motion? Pg. 312

You can show the motion of an object on a line graph in which you plot distance

versus time. • Time is shown on the x-axis (the

horizontal axis)

• Distance is shown on the y-axis (the vertical axis).

• Each point on the line represents the distance an object has traveled during a particular time.

The steepness of a line on a graph is its

slope.

How Do You Graph Motion? Pg. 312

The slope tells you how fast one variable changes in relation to the other variable in the graph.

• In other words, slope tells you the rate of change.

• Since speed is the rate at which distance changes over time, the slope of a distance-versus-time graph represents speed.

• To calculate the slope of a line, divide the rise (vertical change between two points) by the run (horizontal change between the same two points).

Slope= Rise

Run

Figure 4--Speed and Velocity pg. 312

Constant SpeedThe graph shows the motion of a

jogger.

1.What is the jogger's speed?

___________________

1. On the same graph, draw a line that represents the motion of a jogger that moves at a constant speed of 100 m/min.

Figure 5 Speed and Velocity pg. 313Changing Speed

The graph shows how the speed of a jogger varies during her second day of training. Find the rise, the run, and the slope for each

segment of the graph?