III.1.4. Types of movement.

Types of movement

A) Classification of the movement according to the trajectory:

• Rectilinear motion, in which the trajectory is a straight line.

• Curvilinear motion, in which the trajectory is a curved line.

• Rotational motion, in which the trajectory is a circle or a circular arc.

B) Classification of movement by speed:

• Uniform motion, in which the speed is constant (its value does not change).

• Varied accelerated movement, in which the speed increases.

• Various braking movement, in which the speed decreases.

Uniform rectilinear motion is the motion in which the trajectory is a straight line and the speed is constant.

In uniform rectilinear motion:

• The mobile travels equal distances in equal time intervals.

• The current speed is equal to the average speed.

• Speed maintains its numerical value, direction and sense of movement.

To determine the law of uniform rectilinear motion, we start from the velocity formula, noting with x₀ = initial position, with x = final position, with t₀ = initial moment and with t = final moment.

The law of uniform rectilinear motion:

x = x₀ + v (t - t₀) when the mobile moves away from the landmark

x = x₀ - v (t - t₀) when the mobile is approaching the landmark.

🔓 Solved Problem

1. Luiza's coach timed her movement on the 100 m track and entered the movement data in the following table.

a) What kind of movement does Luiza have?

b) Calculate the average speed.

c) Determine the law of motion.

Solution:

a) We notice in the table that Luiza travels equal distances (25 m) in equal time intervals (3 s). So Luiza has a rectilinear and uniform movement. Attention, if the body has a constant speed, the trajectory must be rectilinear. In curvilinear and rotational motion, the speed cannot be constant.

b)

When speed gives us with period, it is good to work with an irreducible fraction

c) We replace in the law of motion x₀, v and t₀ :

🔐 Homework

1. In the following table the data of the movement of a mobile are entered.

Is required:

a) What kind of movement does the mobile have? Why?

b) Calculate the average speed.

c) Determine the law of motion.