velocity

using vector arrows to represent velocity

The arrows in the Figure 1.1 represent the velocity of three different objects. Arrows A and B are the same length but point in different directions. They represent objects moving at the same speed but in different directions. Arrow C is shorter than arrow A or B but points in the same direction as arrow A. It represents an object moving at a slower speed than A or B but in the same direction as A.

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differences in velocity

Objects have the same velocity only if they are moving at the same speed and in the same direction. Objects moving at different speeds, in different directions, or both have different velocities. Look again at arrows A and B from the Figure 1.1. They represent objects that have different velocities only because they are moving in different directions. A and C represent objects that have different velocities only because they are moving at different speeds. Objects represented by B and C have different velocities because they are moving in different directions and at different speeds. Q: Jerod is riding his bike at a constant speed. As he rides down his street he is moving from east to west. At the end of the block, he turns right and starts moving from south to north, but hes still traveling at the same speed. Has his velocity changed? A: Although Jerods speed hasnt changed, his velocity has changed because he is moving in a different direction. Q: How could you use vector arrows to represent Jerods velocity and how it changes? A: The arrows might look like this:

speed and direction

Speed tells you only how fast or slow an object is moving. It doesnt tell you the direction the object is moving. The measure of both speed and direction is called velocity. Velocity is a vector. A vector is measurement that includes both size and direction. Vectors are often represented by arrows. When using an arrow to represent velocity, the length of the arrow stands for speed, and the way the arrow points indicates the direction. Click image to the left or use the URL below. URL:

calculating average velocity

You can calculate the average velocity of a moving object that is not changing direction by dividing the distance the object travels by the time it takes to travel that distance. You would use this formula: velocity = distance time This is the same formula that is used for calculating average speed. It represents velocity only if the answer also includes the direction that the object is traveling. Lets work through a sample problem. Tonis dog is racing down the sidewalk toward the east. The dog travels 36 meters in 18 seconds before it stops running. The velocity of the dog is: distance time 36 m = 18 s = 2 m/s east velocity = Note that the answer is given in the SI unit for velocity, which is m/s, and it includes the direction that the dog is traveling. Q: What would the dogs velocity be if it ran the same distance in the opposite direction but covered the distance in 24 seconds? A: In this case, the velocity would be: distance time 36 m = 24 s = 1.5 m/s west velocity =

instructional diagrams

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questions

velocity is a vector.

-->  a. true

b. false

if you represent velocity with an arrow, the length of the arrow represents

-->  a) speed.

b) distance.

c) direction.

d) acceleration.

the si unit for velocity is km/h.

a. true

-->  b. false

diagram questions

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