![]() Uniform circular motion is the motion of an object in a circle with a constant or uniform speed. In such a situation as this, the motion of your car could be described as experiencing uniform circular motion. And suppose that as you drove, your speedometer maintained a constant reading of 10 mi/hr. Suppose that you were driving a car with the steering wheel turned in such a manner that your car followed the path of a perfect circle with a constant radius. Lesson 1 of this study will begin with the development of kinematic and dynamic ideas that can be used to describe and explain the motion of objects in circles. ![]() We will see that the beauty and power of physics lies in the fact that a few simple concepts and principles can be used to explain the mechanics of the entire universe. Kinematic concepts and motion principles will be applied to the motion of objects in circles and then extended to analyze the motion of such objects as roller coaster cars, a football player making a circular turn, and a planet orbiting the sun. In this unit, we will see that these same concepts and principles can also be used to describe and explain the motion of objects that either move in circles or can be approximated to be moving in circles. The same concepts and principles used to describe and explain the motion of an object can be used to describe and explain the parabolic motion of a projectile. The motion of a moving object can be explained using either Newton's Laws ( Unit 2 of The Physics Classroom) and vector principles ( Unit 3 of The Physics Classroom) or by means of the Work-Energy Theorem ( Unit 5 of The Physics Classroom). Lesson 6 of this unit will focus upon the use of the kinematic equations to predict the numerical values of unknown quantities for an object's motion.Any moving object can be described using the kinematic concepts discussed in Unit 1 of The Physics Classroom. For example, if the acceleration value and the initial and final velocity values of a skidding car is known, then the displacement of the car and the time can be predicted using the kinematic equations. In this manner, the kinematic equations provide a useful means of predicting information about an object's motion if other information is known. If the values of three of the four variables are known, then the value of the fourth variable can be calculated. Each of the kinematic equations include four variables. They can never be used over any time period during which the acceleration is changing. The equations can be utilized for any motion that can be described as being either a constant velocity motion (an acceleration of 0 m/s/s) or a constant acceleration motion. The kinematic equations are a set of four equations that can be utilized to predict unknown information about an object's motion if other information is known. In such an instance as this, the unknown parameters can be determined using physics principles and mathematical equations (the kinematic equations). However you do not know the displacement that your car would experience if you were to slam on your brakes and skid to a stop and you do not know the time required to skid to a stop. ![]() For example as you approach the stoplight, you might know that your car has a velocity of 22 m/s, East and is capable of a skidding acceleration of 8.0 m/s 2, West. ![]() It is often the case that only a few parameters of an object's motion are known, while the rest are unknown. However, such completeness is not always known. These two statements provide a complete description of the motion of an object. And if a second car is known to accelerate from a rest position with an eastward acceleration of 3.0 m/s 2 for a time of 8.0 seconds, providing a final velocity of 24 m/s, East and an eastward displacement of 96 meters, then the motion of this car is fully described. For example, if a car is known to move with a constant velocity of 22.0 m/s, North for 12.0 seconds for a northward displacement of 264 meters, then the motion of the car is fully described. Knowledge of each of these quantities provides descriptive information about an object's motion. There are a variety of quantities associated with the motion of objects - displacement (and distance), velocity (and speed), acceleration, and time. These equations are known as kinematic equations. In Lesson 6, we will investigate the use of equations to describe and represent the motion of objects. The variety of representations that we have investigated includes verbal representations, pictorial representations, numerical representations, and graphical representations ( position-time graphs and velocity-time graphs). The goal of this first unit of The Physics Classroom has been to investigate the variety of means by which the motion of objects can be described.
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