Part 3.  Natural Method of Describing Motion

The continuous curve described by moving particle with respect to a given frame of reference is called the path of that particle.

If the path is a straight line, the motion is said to be rectilinear, if the path is a curve, the motion is curvilinear.

The natural method of describing motion is convenient when the particle’s path is known at once.

In order to describe the motion of a particle by the natural method, a problem must state: (1) the path of the particle; (2) the origin of the path, showing the positive and negative directions; (3) the equations of the particle’s motion along the path in the form s = f(t) (Fig.2).

                           

             

Fig. 2

Ex. 8. Answer the following questions.

1. Give the definition of  the path of a particle.

2. What motion is rectilinear?

3. What motion is curvilinear?

4. When is the natural method  convenient?

 

Ex. 9. Say whether the following statements are True or False.

1. Kinematics doesn’t take into account the mass of bodies.

2. Kinematics takes into account the forces acting on bodies.

3. When the particle moves, the vector   changes with time only in direction.

4. When motion takes place, the three coordinates remain the same within the frame of reference.

5. The motion is said to be rectilinear if the path of a moving particle is a straight line.

 

Ex. 10. Complete the following sentences with the information from the text.

1. Coordinate system is…

2. The continuous curve described by moving particle with respect to a given frame of reference is…

3. The motion of the body is considered with respect to …

4. The body is said to be in motion relative to the given frame of reference if…

5. The locus of the tip of vector   defines…

 

Ex.1 1. Put  the questions to the following answers.

1. It is the continuous curve described by  a moving particle with respect to a given frame of reference

2.  The path of the rectilinear motion is a straight line.

3. The natural method of describing motion is convenient when we know the particle’s path.

4.  We must know the coordinates of a particle for any moment of time.

 

Ex.1 2. Match the verbs and nouns or noun phrases they can be used with. Compose 5  sentences with  any of these expressions.

       

	Verbs:		Nouns / noun phrases
1	be directed	a	the positive direction
2	calculate	b	a characteristic of  a motion
3	describe	c	along a chord
4	introduce	d	the path of a particle
5	obtain	e	the motion
6	occupy	f	the average velocity
7	show	g	a position
8	state	h	a concept