 # The study of moving things…. What is Kinematics? Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs,

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The study of moving things…

What is Kinematics? Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs, and equations. Kinematics is a branch of mechanics. The goal of any study of kinematics is to develop sophisticated mental models that serve to describe (and ultimately, explain) the motion of real-world objects.

Scalars and vectors Scalars are quantities that are fully described by a magnitude (or numerical value) alone. For example: time, distance, speed… Vectors are quantities that are fully described by both a magnitude and a direction. For example: velocity, displacement, acceleration…

Check your understanding… On a separate piece of paper, identify which of the following quantities is a scalar or vector: 1. 5 m.scalarvector 2. 30 m/sec, Eastscalarvector 3. 5 mi., Northscalarvector 4. 20 degrees Celsiusscalar vector 5. 256 bytesscalarvector 6. 4000 Caloriesscalarvector

Check your understanding… On a separate piece of paper, identify which of the following quantities is a scalar or vector: 1. 5 m.Scalarvector 2. 30 m/sec, Eastscalarvector 3. 5 mi., Northscalarvector 4. 20 degrees Celsiusscalar vector 5. 256 bytesscalarvector 6. 4000 Caloriesscalarvector

Distance and displacement Distance and displacement are similar, yet very different. Distance is a scalar quantity that refers to “how much ground is covered” during the motion. It counts every step. Displacement is a vector quantity that refers to “how far out of place an object is”. It is the object’s overall change in position.

Check your understanding… A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. What is the teacher’s distance travelled? What is the teachers displacement?

Check your understanding… Distance = 12 meters. Displacement = 0 meters. During the course of the motion, he has "covered 12 meters of ground" (distance = 12 m). Yet when he is finished walking, he is not "out of place" (he is back to his original position) i.e., there is no displacement for his motion (displacement = 0 m). Displacement, being a vector quantity, must give attention to direction. The 4 meters east cancels the 4 meters west; and the 2 meters south cancels the 2 meters north. Vector quantities such as displacement are direction aware. Scalar quantities such as distance are ignorant of direction. In determining the overall distance traveled by the physics teachers, the various directions of motion can be ignored.

Speed and velocity… Speed is defined as “how fast an object moves”. Speed can be calculated using the following equation: Speed = distance / time Remember, speed is a scalar quantity. Velocity is defined as “how fast an object’s position changes”. Velocity can be calculated using the following equation: Velocity = displacement / time Remember, velocity is a vector quantity.

Major difference between speed and velocity… The most essential difference between speed and velocity is DIRECTION. Velocity is a vector quantity. Velocity is direction aware. You must keep track of direction for velocity. It is not enough to say that an object has a velocity of 55 mi/hr. It would be correct, however to say that the velocity is 55 mi/hr, EAST. REMEMBER: Speed is a scalar quantity and does not keep track of direction, but velocity is a vector quantity and is direction aware.

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