Descriptors of Motion PDF

Descriptors of Motion Objective describe the motion of an object in terms of distance At the end 1 or displacement, speed or of the velocity, and acceleration. lesson, you should be able to:  Learn about It! Motion of an Object How an object mo...

Descriptors of Motion Objective describe the motion of an object in terms of distance At the end 1 or displacement, speed or of the velocity, and acceleration. lesson, you should be able to:  Learn about It! Motion of an Object How an object moves is described relative to something else. Describing motion requires a point of reference (reference frame). In other words, the distance travelled by an object, how fast the object is travelling, and the direction in which the object travels to, is measured with respect to a point of reference.  Learn about It! Motion of an Object Consider the image below: Different positions of a truck at varying time intervals.  Learn about It! Motion of an Object Different positions of a truck at varying time intervals. Suppose you take the 0 m-mark at time t = 0 s as the point of reference in figure 1. After 2 seconds, the truck travelled a distance of 20 meters. However, if you take the 20 m-mark as a point of reference, you will find that the car will cover a distance of 10 meters after a second.  Learn about It! Distance and Displacement Contrary to the distance travelled by an object, its displacement is defined by the change in position from its starting point to the final point.  Learn about It! Distance and Displacement Refer to the image below: The displacement of a ball after being rolled several times.  Learn about It! The displacement of a ball after being rolled several times. A ball was rolled 2 meters to the right and then was rolled 1 meter to the left. After which, it was rolled 2 meters to the right. In this particular scenario, the total distance travelled by the ball is given by 2 m + 1 m + 2 m = 5 m.  Learn about It! The displacement of a ball after being rolled several times. However, the change in its position from its starting point is only 3 meters. Therefore, the displacement of the ball is 3 meters to the right. To get the displacement of an object, the direction in which the object moves to is being considered.  Learn about It! Speed Another way to describe motion of an object is by means of its speed. Speed measures how far an object travels over a given amount of time.  Learn about It! Speed It is measured as distance per unit of time. For example, if a car travels 300 kilometers in 3 hours, you say that the car travels with a speed of 100 km/hr. Units such as miles per hour and meters per second also measure speed.  Learn about It! Velocity The terms “speed” and “velocity” are often interchanged in ordinary language. In Physics however, you must take note of the difference between these two quantities.  Learn about It! Velocity Speed is simply a positive number measured in distance per unit of time. Meanwhile, velocity is used to indicate both the magnitude (numerical value) of how fast an object moves, and the direction in which the object is moving to. It can be generalized that speed is the distance travelled per unit of time whereas velocity is a measure of the displacement travelled per unit of time.  Learn about It! Acceleration In our everyday observation of motion, you notice that the rate at which objects move is not always the same. For instance, the speed of a ball at the moment you drop it from a certain height is different from its speed the moment it touches the ground.  Learn about It! Acceleration Also, you can observe that if you toss the ball upwards, its speed gradually decreases until it momentarily stops on a certain peak. These instances, along with many other “speeding up” and “slowing down” phenomena, are called acceleration.  Learn about It! Acceleration A ball accelerates after being dropped from a certain height.  Learn about It! Acceleration Acceleration is defined as the change in velocity per unit of time. Therefore, acceleration also considers the direction of motion. In one-dimensional motion (motion along a straight line), plus (+) and minus (–) signs are used to indicate the direction of the acceleration.  Learn about It! Acceleration The sign is dependent on the motion of the object and point of reference. The plus sign is used for the positive x direction (rightward motion) and minus sign for the negative x direction (leftward motion).  Learn about It! Signs of Acceleration The sign of the acceleration of the car depends on the change of its velocity. Key Points Distance is the length of the path travelled by an object. 1 Displacement is the change in position of an object from initial to final point. Speed is a measure of the magnitude of how fast an object travels in a given time. 2 Velocity is a measure of both the magnitude and direction. Key Points Acceleration is defined as the change in velocity per unit of time. ○ When an object is speeding up, the acceleration is 3 in the same direction as the velocity. ○ When an object is slowing down, the acceleration is in the opposite direction of the velocity.  Check Your Understanding Write T if the statement is true and F if it is false. 1. Distance and displacement both describes the length of the path travelled by an object. 2. Speed describes how fast an object moves. 3. The sign of the acceleration of an object is negative if it is speeding up. 4. An object slowing down has a positive acceleration. 5. Velocity indicates not only the magnitude of the speed of an object but also the direction in which it is moving.  Challenge Yourself If an object has a negative acceleration, what does this indicate about the motion of the object?  Bibliography Faughn, Jerry S. and Raymond A. Serway. 2006. Serway’s College Physics, 7th Edition. Singapore: Brooks/Cole Gardose-Figueras, Geraldine. 2009. Science Fundamentals for High School IV: Physics. Philippines: Trinitas Publishing Inc. Giancoli, Douglas C. 1985. Physics: principles with applications. Englewood Cliffs, N.J.: Prentice-Hall. Hewitt, Paul G. 2002. Conceptual Physics, 9th Edition. Singapore: Pearson Education