2.1.1 Describing Motion

Question 1

Describing Motion

Answer 1

• Kinematics is the description of motion.
• Time, t, and position, x, are necessary to describe motion in one dimension.
• The number used to describe position is based on an arbitrary coordinate system, but the position itself is real.
• Be sure you understand how to interpret graphs of motion in terms of actual motion.

Question 2

note

Answer 2

• The goal of this unit is to describe the motion of objects. For example, you would like to predict the motion of a ball tossed in the air. The branch of physics that deals with the description of motion is known as kinematics.
• We begin the study of kinematics by considering motion in one dimension. Examples of one-dimensional motion are a train traveling on a straight track, a car driving on a straight road, and a ball falling to the ground.The variables necessary to describe one-dimensional motion are time (t), which refers to an instant in time, and position(x), which refers to a location with respect to a defined coordinate system.
• In the example on the left, the iguanodon moves at a constant rate from left to right. In this coordinate system the iguanodon moves from 0 to 4 as illustrated by the graph. As time (t)increases, the iguanodon’s position from the origin also increases.
• In the example on the right, the iguanodon’s motion is the same: he moves at a constant rate from left to right. In this coordinate system, which increases toward the left, the iguanodon moves from 0 to –4.
• The graph illustrates that as time (t) increases, the iguanodon’s position from the origin decreases.The number used to describe the position of the iguanodon is arbitrary; the iguanodon’s physical position itself is real.

Question 3

The graph shows the motion of a theoretical particle in a particle accelerator.

Which of the following statements is not correct?

Answer 3

The particle does not experience any instantaneous changes in position

Question 4

Suppose you describe the unidirectional motion of a marble using coordinate system A. Then you describe the exact same motion of the marble using coordinate system B.

Which of the following statements is not correct?

Answer 4

The numbers used to describe the marble’s motion does not change when using the two different coordinate systems

Question 5

The four graphs describe the motion of an object. Which of the following statements is not correct?

Answer 5

You cannot gather any information about speed changes from the graphs because they are based on position x versus time t

Question 6

A one-dimensional function j (t) describes a car’s motion in the j-direction as a function of time t, as shown in the drawing. Which of the following does not correctly describe the motion of the car?

Answer 6

The time t is a time interval over which the car’s position is observed

Question 7

One of the simplest types of motion is unidirectional motion. Which of the following is the worst example of unidirectional motion?

Answer 7

The motion of ventilation heat as it travels from a furnace to various rooms in a home

Question 8

Which of the following best describes kinematics?

Answer 8

Kinematics is a part of mechanics that involves the description of motion

Question 9

Suppose a ball was initially at y0. It then moved in the negative direction and rested for a while. It then moved again in the negative direction. Finally the ball returned to its original position. Which graph best represents the motion of the ball?

Answer 9

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Question 10

Which of the following statements related to kinematics is not correct?

Answer 10

An instant in time lasts one second.

Question 11

Which of the following statements is correct?

Answer 11

The coordinate system used to describe an object’s position is arbitrary. The actual position of an object is real and physical