1. What is Sound? Sound is a form of energy which produces a sensation of hearing in our ears. Sound is produced by vibrating objects. Examples include vibrating tuning fork, vocal cords in humans, bells, musical instruments, etc. Vibration: Rapid to-and-fro (back and forth) motion of an object. Short Question: Can sound be produced without vibration? Answer: No, sound cannot be produced without vibration. 2. Medium of Sound The substance through which sound travels is called a medium . Sound can travel through solids, liquids, and gases but cannot travel through vacuum . Process of Sound Propagation: When an object vibrates, it makes the air particles around it vibrate. These air particles move back and forth from their original (rest) position. The vibrating air particles push nearby air particles. This causes the nearby particles to also start vibrating. In this way, vibrations pass from one particle to another. This process continues through the medi...
Work
Work is done when a force causes displacement in the direction of the applied force.
Condition for work done:
- Force should be applied on the body.
- Body should be displaced.
Work done in moving a body is equal to the product of force and displacement of the body in the direction of the force.
Formula: W = F × s
SI Unit of Work: Joule (J) = N·m
1 Joule: 1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.
1 Joule (J) = 1 Newton (N) × 1 metre (m)
- Work done by a force can be either positive or negative.
- Work done is negative when the force acts opposite to the direction of displacement.
- Work done is positive when the force is in the direction of displacement.
Energy
- The energy possessed by an object is its capacity for doing work.
- S.I. unit of energy is Joule (J).
- 1 Joule of energy is the amount of energy required to do 1 Joule of work.
1 kiloJoule = 1000 Joules
Kinetic Energy
Kinetic energy is the energy possessed by an object due to its motion. The kinetic energy of an object increases with its speed.
Derivation for the expression of kinetic energy:
Consider an object of mass m moving with a uniform velocity u. Let it be displaced through a distance s under a constant force. Its velocity changes from u to v. Let acceleration be a.
Using equations of motion:
v² − u² = 2as
We know, F = m × a
Work done = Force × Displacement
W = F × s
= m × a × s
= m × (v² − u²) / 2
Thus, the kinetic energy possessed by an object of mass m and moving with a velocity v is:
Kinetic Energy (KE) = ½ mv²
Potential Energy
Potential energy is the energy an object has due to its position, properties, or forces acting on it. Examples include: a stretched rubber band or a ball at a height.
Consider an object of mass m raised through a height h from the ground.
The minimum force required = weight of the object = mg.
Work done against gravity:
W = force × displacement = mg × h = mgh
Potential Energy (Ep) = mgh
- The work done by gravity depends only on the difference in vertical heights, not on the path taken by the object.
If a block is moved from A to B along different paths but the height h is the same, work done = mgh in both cases.
Law of Conservation of Energy
Energy cannot be created or destroyed. It can only be transformed from one form to another. In an isolated system, the total energy remains constant.
Conversion of Potential and Kinetic Energy
Consider an object of mass m falling freely from a height h.
At the start:
- Potential Energy (PE) = mgh
- Kinetic Energy (KE) = 0 (since velocity = 0)
- Total Energy = mgh
During the fall:
- Potential Energy decreases as height decreases.
- Kinetic Energy increases as velocity increases.
Just before reaching the ground:
- PE = 0
- KE is maximum
Total energy remains constant during the fall:
Potential Energy + Kinetic Energy = Constant
mgh + ½ mv² = Constant
Power
Power is defined as the rate of doing work. It is the amount of energy consumed per unit time.
Unit: Watt (W) = Joule/second (J/s)
1 Watt is defined as the power required to do 1 Joule of work per second.
1 Watt (W) = 1 Joule/second (J/s)
1 kilo Watt (kW) = 1000 W = 1000 J/s
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