Liquid — In a liquid, particles will flow or glide over one another, but stay toward the bottom of the container. The attractive forces between particles are strong enough to hold a specific volume but not strong enough to keep the molecules sliding over each other.
Gas — In a gas, particles are in continual straight-line motion. The kinetic energy of the molecule is greater than the attractive force between them, thus they are much farther apart and move freely of each other. In most cases, there are essentially no attractive forces between particles. This means that a gas has nothing to hold a specific shape or volume. A fourth state of matter, called plasma, exists when a gas becomes ionized.
What words would you use to describe such a motion? How does the motion of the bobblehead change over time? How does the motion of one bobblehead differ from the motion of another bobblehead? What quantities could you measure to describe the motion and so distinguish one motion from another motion? How would you explain the cause of such a motion? Why does the back and forth motion of the bobblehead finally stop? These are all questions worth pondering and answering if we are to understand vibrational motion.
These are the questions we will attempt to answer in Section 1 of this chapter. Like any object that undergoes vibrational motion, the bobblehead has a resting position. The resting position is the position assumed by the bobblehead when it is not vibrating. The resting position is sometimes referred to as the equilibrium position. When an object is positioned at its equilibrium position, it is in a state of equilibrium.
As discussed in the Newton's Law Chapter of the Tutorial , an object which is in a state of equilibrium is experiencing a balance of forces. All the individual forces - gravity, spring, etc. When a bobblehead is at the equilibrium position, the forces on the bobblehead are balanced. The bobblehead will remain in this position until somehow disturbed from its equilibrium. If a force is applied to the bobblehead, the equilibrium will be disturbed and the bobblehead will begin vibrating.
We could use the phrase forced vibration to describe the force which sets the otherwise resting bobblehead into motion. In this case, the force is a short-lived, momentary force that begins the motion.
The bobblehead does its back and forth, repeating the motion over and over. Each repetition of its back and forth motion is a little less vigorous than its previous repetition.
If the head sways 3 cm to the right of its equilibrium position during the first repetition, it may only sway 2. And it may only sway 2. And so on. The extent of its displacement from the equilibrium position becomes less and less over time. Because the forced vibration that initiated the motion is a single instance of a short-lived, momentary force, the vibrations ultimately cease. The bobblehead is said to experience damping.
Damping is the tendency of a vibrating object to lose or to dissipate its energy over time. The mechanical energy of the bobbing head is lost to other objects. Without a sustained forced vibration, the back and forth motion of the bobblehead eventually ceases as energy is dissipated to other objects.
A sustained input of energy would be required to keep the back and forth motion going. After all, if the vibrating object naturally loses energy, then it must continuously be put back into the system through a forced vibration in order to sustain the vibration. A vibrating bobblehead often does the back and forth a number of times. The vibrations repeat themselves over and over. As such, the bobblehead will move back to and past the equilibrium position every time it returns from its maximum displacement to the right or the left or above or below.
This begs a question - and perhaps one that you have been thinking of yourself as you've pondered the topic of vibration.
If the forces acting upon the bobblehead are balanced when at the equilibrium position, then why does the bobblehead sway past this position? Why doesn't the bobblehead stop the first time it returns to the equilibrium position?
The answer to this question can be found in Newton's first law of motion. Like any moving object, the motion of a vibrating object can be understood in light of Newton's laws. According to Newton's law of inertia, an object which is moving will continue its motion if the forces are balanced. Put another way, forces, when balanced, do not stop moving objects. So every instant in time that the bobblehead is at the equilibrium position, the momentary balance of forces will not stop the motion.
The bobblehead keeps moving. Signup with Email. Gender Male Female. Create Account. Already Have an Account? What is chemical nature of matter? Class 9 Question. Answer to Question. Shiulie Ghosh Jul 17, Nature of Matter. Solids: Solids are all those substances having their particles very close to each other. There exist strong intermolecular forces between these particles.
The particles are firmly held in their positions. These particles have only vibratory motion. Solids have a definite shape and definite volume. Examples include Wood, iron, aluminium etc. Liquids: Liquids comprise of all those substances with weak intermolecular forces.
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