Speed and Velocity Speed - the distance traveled divided by the time taken to travel the distance.

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# Speed and Velocity Speed - the distance traveled divided by the time taken to travel the distance. - PowerPoint PPT Presentation

The speed of an in-line skater is usually described in meters per second. The speed of a car is usually described in kilometers per hour. Speed and Velocity Speed - the distance traveled divided by the time taken to travel the distance. formula : speed = distance / time (s=d/t)

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Presentation Transcript
The speed of an in-line skater is usually described in meters per second. The speed of a car is usually described in kilometers per hour.

Speed and Velocity

• Speed- the distance traveled divided by the time taken to travel the distance.
• formula: speed = distance/time (s=d/t)
• units: meters per second (m/s)- standard SI unit, (km/hr), (cm/s)
• A swimmer who swims 100 m in 56s

100 m

?

56s

d

d=

s=

t=

s t

A cyclist travels a total distance of 45 km at an average speed of 15 km/hr. How long did it take for him to go this distance?

45km

15 km/hr

?

d

d=

s=

t=

s t

An object in motion can change speeds many times as it moves from one point to another, speeding up or slowing down

• Average speed- total distance traveled divided by total time taken
• Constant speed- When an object covers equal distances in equal amounts of time.
• A race car travels at a constant speed of 96 m/s means for every second the car goes exactly 96 meters.
• Instantaneous speed- the rate at which an object is moving at a given instant in time.

Speed

The speedometer in a car measures the car’s instantaneous speed.

Note the scale markings are given both in km/h and miles per hour, mph.

Graphing motion

• You can show the motion of an object on a line graph in which you plot distance verses time.
• Slope- the steepness of a line on a graph
• Calculating slope (pg .23)
• Formula :
• Unit of measure:
The slope of a line on a distance-time graph is speed
• A steeper slope on a distance-time graph indicates a higher speed.

Velocity- speed of an object AND its direction of motion

• Velocity is also a vector that shows changes in motion
• Vectors of varying lengths, each vector corresponding to the velocity at a particular instant, can represent motion.
• A longer vector represents a faster speed, and a shorter one a slower speed.
• Vectors point in different directions to represent direction at any moment

Velocity

A cheetah’s speed may be as fast as 90 km/h. To describe the cheetah’s velocity, you must also know the direction in which it is moving.

Velocity

As the sailboat’s direction changes, its velocity also changes, even if its speed stays the same.

Assessment Questions

• A woman jogs 10 kilometers in one hour, stops at a restaurant for one hour, and then walks 10 kilometers in two hours. What is her average speed for the outing?
• 0.2 km/h
• 4 km/h
• 5 km/h
• 10 km/h

Assessment Questions

• A woman jogs 10 kilometers in one hour, stops at a restaurant for one hour, and then walks 10 kilometers in two hours. What is her average speed for the outing?
• 0.2 km/h
• 4 km/h
• 5 km/h
• 10 km/hANS: C

Assessment Questions

• Lisa plotted time on the x-axis of a line graph and distance on the y-axis. What does the slope of her graph represent?
• total distance traveled
• velocity
• speed
• displacement

Assessment Questions

• Lisa plotted time on the x-axis of a line graph and distance on the y-axis. What does the slope of her graph represent?
• total distance traveled
• velocity
• speed
• displacementANS: C

Assessment Questions

• Lisa plotted time in seconds on the x-axis of a line graph and distance in centimeters on the y-axis. Her plot showed a straight line from (0,0) to (10, 20). What is the speed?
• 0.5 cm/s
• 2 cm/s
• 10 cm/s
• 20 cm/s

Assessment Questions

• Lisa plotted time in seconds on the x-axis of a line graph and distance in centimeters on the y-axis. Her plot showed a straight line from (0,0) to (10, 20). What is the speed?
• 0.5 cm/s
• 2 cm/s
• 10 cm/s
• 20 cm/sANS: B

Assessment Questions

• Two velocities of an object are combined by using
• division of the larger velocity by the smaller velocity.
• addition of the two speeds.

Assessment Questions

• Two velocities of an object are combined by using
• division of the larger velocity by the smaller velocity.
• addition of the two speeds.