Motion in Nature

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Welcome to class! 

In today’s class, we will be talking about motion in nature. Enjoy the class!

Motion in Nature

Introduction to motion

Motion plays important roles in our daily lives. We move from one place to another either by walking or by moving in cars, aircraft, etc. Videos tapes and tape recorders can only operate when in motion; the air around us is in constant motion; the earth is also moving by rotating about it axis around the sun; electrons must be in motion in a wire for electric current to exist. This gives us an idea of what motion is. Let us now attempt a definition for it.

What is motion?

In all the examples given above, one will notice that a change of position is involved in motion. Whenever a body changes its position, it covers some distance and some time interval elapsed. We can thus define Motion as the change in position of a body over some time interval.

Types of motion

Referring to some of the motions mentioned earlier, one observes that theses motions are not of the same nature. For the motion of a car is different from that of the videotape operation. Likewise, the motion of the earth about its own axis is different from the motion of air molecules. Hence we categorize motion into the following types:

1. Translational/Linear Motion
2. Oscillatory/Vibratory/Periodic Motion
3. Rotational Motion

• Translatory motion:

“In translational motion, a body moves along a line without any rotation. The line may be straight or curved.”Watch how various objects are moving. Do they move along a straight line? Do they move along a circle? A car moving in a straight line has transnational motion. Similarly, an aeroplane moving straight is in translational motion. Translatory motion is further divided into:

1. Linear motion
2. Circular motion and
3. Random motion.

Examples of translatory motion 

1. Motion of train
2. Motion of earth
3. Motion of birds
4. Motion of insects
5. Motion of aeroplane
6. The motion of gas molecules

(a) Linear (rectilinear) motion:

“Straight-line motion of a body is known as its linear motion. In linear motion, the particles move from one point to another in either a straight line or a curved path. The linear motion depending on the path of motion and is further divided as follows

• Rectilinear Motion – The path of the motion is a straight line.
• Curvilinear Motion – The path of the motion is curved. 

Linear Motion

 Linear motion examples in daily life

1. The motion of the car on the road
2. Motion of football
3. Sliding a boy in a straight line is the example of linear motion
4. The motion of the train, etc.

(b) Circular motion:

“The motion of an object in a circular path is known as circular motion.”A toy train moving on a circular track. Earth revolving around the sun is an example of circular motion.

Circular Motion

bicycle or a car moving along a circular track possesses circular motion. The motion of the moon around the earth is also an example of circular motion.

 Examples of circular motion in daily life

1. The motion of the electron around the nucleus
2. The motion of toy car on the circular track
3. The motion of planets around the sun

(c) Random motion:

“The disordered or irregular motion of a body is called random motion.”Have you noticed the type of motion of insects and birds? Their movements are irregular and disorder. The motion of insects and birds is random motion. The motion of dust or smoke particles in the air is also random motion. The Brownian motion of a gas or liquid molecules along a zig-zag is also an example of random motion.”The random motion of gas molecules is called Brownian motion.”

• Rotatory (Rotational) motion:

“The spinning motion of a body about its axis is called its rotatory motion.”

Rotatory motion is the motion that occurs when a body rotates on its own axis. A few examples of the rotatory motion are as follows:

1. The motion of the earth about its own axis around the sun is an example of rotary motion.
2. While driving a car, the motion of wheels and the steering wheel about its own axis is an example of rotatory motion.

 

Rotational Motion

• Oscillatory (Periodic/vibratory) motion:

Periodic motion is a motion that repeats itself after an equal interval of time. Some examples of periodic motion include:

1. The motion of the earth in its orbit around the sun which repeats itself after a time period of one year.
2. Movement of clock pendulum which repeats itself after a fixed time period.
3. The motion of rocking chair, a bouncing ball, a vibrating tuning fork, a swing in motion are few examples of bodies/objects executing the periodic motion.
4. When a child on a swing is pushed, the swing moves to and fro about its mean position.
5. The string of the guitar when strummed moves to and fro by its mean position resulting in an oscillatory motion.

Causes of motion

If you pull or push a body, any of the following can happen:

1. The body can start moving if it was initially stationary.
2. The speed of motion can increase or decrease depending on the direction of push or pull.
3. The body, if already moving, can come to a stop.
4. The direction of motion of the body can change.
5. The body can be deformed.

Force is either a push or a pull. It is the one that causes motion. We can thus define force as that which alters the state of rest or motion of a body in a straight line. Note that the force that moves a body can be external or internal. For example, when one hits a ball, that is an external force. On the other hand, for a car to move, the force required is derived from the energy generated within the car. That is, the burning fuel inside the engine of the car generates energy from which the motive force is derived.

Types of force

There are two types of force in nature. These are:

1. Contact force and
2. Non-contact force (Force field)

Contact force:

This is a force that acts in direct physical contact with a body. For an instant, when one pulls or pushes a box, the force is in physical contact with the box.  Another is the force between two rough surfaces in contact, which prevents one from sliding on the other (friction).

Non-contact force:

There are situations where a force acts on a body without the force than actually being in contact with the body. The force act at a distance or through a region around the body. This is called a non-contact force of force field.

 

In our next class, we will be talking about Friction.  We hope you enjoyed the class.

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