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Introduction

Motion means movement. Motion can also be defined as a continuous change in the position of an object. Each type of motion is controlled by a different type of force. Kinematics is the science which studies the motion of objects. This chapter looks at some types of simple and complicated motion.

Main types of simple motion

There are two types of basic motion: translation and rotation. Translation means motion along a path. Rotation means motion around a fixed axis. An axis is the center around which something rotates. As we have mentioned before, each type of motion is controlled by a different type of force. Translation is defined by the net force (sum of different forces) acting on an object. Rotation is defined by torque. Torque is a force which causes the rotation of an object.

Linear motion is the most basic of all motions. Linear motion is the type of motion in which all parts of an object move in the same direction and each part moves an equal distance. Linear motion is measured by speed and direction. Distance travelled by an object per unit of time is called velocity. Example: a moving car.

Rotary motion is motion in a circle. This type of motion is the starting point of many mechanisms. Example: a spinning wheel. Reciprocating motion is back and forth motion. Example: the up and down motion of a yo-yo.

Irregular motion is motion which has no obvious pattern to its movement. Example: a flying bee. Uniform motion is motion at a constant speed in a straight line. Example: a rolling ball.

Very often, objects move by complicated motion. Complicated motion can be broken down into simpler types of motion. An example of complicated motion is a flying Frisbee. The movement of a Frisbee consists of a linear motion and a rotary motion.

Frictional and gravitational forces affect the motion of objects. Gravitational and frictional forces slow down the motion. The frictional force which slows a body in motion is called kinetic friction. When two objects slide past one another, for example, when you push a box across the floor, part of the energy of your pushing moves the box, and part of the energy is lost to kinetic friction. The less textured the surface, the farther the object will move. That happens because smooth surfaces have less frictional force. Friction is affected by the texture of both the surface and the moving object.

What is inertia?

Inertia means a resistance to any change in motion. All objects have inertia. The larger the mass of an object, the more inertia it has. Newton's First Law of Motion states that moving objects will continue moving in the same direction and at the same speed. It also states that objects at rest will remain at rest unless an outside force acts on them.

When the driver of a car puts on the brakes, the car slows down. The people in the car, however, will continue at the same speed the car was going because of their inertia. The seat belt acts as a force to keep the people in place. Seat belts help keep people from getting hurt when a car comes to a sudden stop.