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Distance, Speed Notes. Distance, Speed. There are 4 ways to quantify motion: How far (distance/displacement) How fast (speed/velocity) Direction Acceleration. Distance.
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Distance, Speed • There are 4 ways to quantify motion: • How far (distance/displacement) • How fast (speed/velocity) • Direction • Acceleration
Distance • Distance of motion is the measured movement of one object relative to another. The object we compare to is called the reference object, and is usually the Earth • We should consider the reference object stationary. When an object moves relative to another object, it will have traveled some distance
Distance • Distance is a scalar quantity (magnitude only, no direction)
Displacement • Displacement is the change in position of an object, or the length of a straight line from its initial position to its final position. When an object moves relative to another, it will not necessarily have undergone any displacement.
Displacement • Displacement is a vector quantity (magnitude and direction are described) • Δx = xf - xi
Speed • Speed is described as the rate of movement Average speed = distance / time Example: A race car goes around a 1 mile oval track in 15 seconds. Its average speed would be 240 mi/hr
Speed • Speed is a scalar quantity Traditional Units: • Metric units: m/s • English units: mi/hr, ft/s
Velocity • Velocity is described as the rate of displacement Average velocity = displacement / time Example: A race car goes around a 1 mile oval track in 15 seconds. Its average velocity would be 0 mi/hr.
Velocity • Velocity is a vector quantity. It has the same units as speed, but direction should be signified.
Velocity • If a graph is drawn with displacement on the y-axis and time on the x-axis, the slope of that graph would show the average velocity Slope = rise/run = Δy / Δx = Δx / Δt = Δd / Δt = v ave
Velocity • Therefore, a steep positive slope corresponds to a large average velocity, a steep negative slope would correspond to a large negative average velocity, a flatter positive slope would correspond to a smaller positive average velocity, etc.
Velocity vave = Δx / Δt = Δd / Δt = (xf – xi) / (tf – ti) Instantaneous Velocity: Velocity at a given instant in time. This cannot be calculated without knowing the constant acceleration or using calculus.