If an object is moving rightwards, then its velocity is described as being rightwards. If an object is moving downwards, then its velocity is described as being downwards. Note that speed has no direction it is a scalar and the velocity at any instant is simply the speed value with a direction. Let's begin implementing our understanding of these formulas with the following problem:. Q: While on vacation, Lisa Carr traveled a total distance of miles.
Her trip took 8 hours. What was her average speed? That was easy! Lisa Carr averaged a speed of 55 miles per hour. Yet, she averaged a speed of 55 miles per hour. The above formula represents a shortcut method of determining the average speed of an object.
Since a moving object often changes its speed during its motion, it is common to distinguish between the average speed and the instantaneous speed. The distinction is as follows. You might think of the instantaneous speed as the speed that the speedometer reads at any given instant in time and the average speed as the average of all the speedometer readings during the course of the trip. Moving objects don't always travel with erratic and changing speeds. Occasionally, an object will move at a steady rate with a constant speed.
That is, the object will cover the same distance every regular interval of time. If her speed is constant, then the distance traveled every second is the same. The runner would cover a distance of 6 meters every second. If we could measure her position distance from an arbitrary starting point each second, then we would note that the position would be changing by 6 meters each second.
This would be in stark contrast to an object that is changing its speed. An object with a changing speed would be moving a different distance each second. The data tables below depict objects with constant and changing speed. Now let's consider the motion of that physics teacher again. The physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. The entire motion lasted for 24 seconds.
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Your name: is required Error: This is required. Your email: is required Error: This is required Error: Not a valid value. Send to: is required Error: This is required Error: Not a valid value. In a typical hour of driving, the speed recorded by the speedometer changes constantly, and the actual distance you travel in an hour is an average of all these speeds.
The total distance you travel in a unit of time, such as an hour, is your average speed S av :. The speed displayed on the speedometer is your instantaneous speed S I. Physicists express instantaneous speed by defining it as the change in position x between two time intervals, t 1 and t 2 and letting the time interval approach zero. For physicists, the most accurate expression for instantaneous speed is. People often use the words speed and velocity interchangeably, but they don't mean the same thing.
Velocity is a vector quantity, which means it has a directional component, whereas speed is a scalar quantity which does not take direction into account.
To see why direction is important, consider the difference in time it takes to drive between two points on a straight road and a winding one. If the road is straight, you can average all the instantaneous speeds recorded by the speedometer and get the same average speed as you would by dividing the total distance by the total time. If the road is windy, however, these two numbers will be different. This is because the directional component of the velocity toward your destination decreases every time the road veers to the left or right.
Velocity is sometimes denoted by the letter v with an arrow over it to signify that it's a vector quantity, but the arrow isn't really necessary. By definition, velocity has a directional component.
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