Understanding Kinetic Energy

Kinetic energy is the energy that an object possesses due to its motion. If an object is moving, it has kinetic energy. The amount of kinetic energy depends on the object's mass and its velocity (speed). The formula for kinetic energy ($KE$) is given by:

$$KE = \frac{1}{2}mv^2$$

where '$m$' is the mass of the object and '$v$' is its velocity.

Analyzing the Options for Kinetic Energy

Let's examine each option to see which one represents energy due to motion:

Option 1: Water in an overhead tank

Water stored in an overhead tank is stationary. It is high above the ground, so it possesses potential energy due to its position (gravitational potential energy). It is not moving, hence it does not have kinetic energy.

Option 2: Wound up spring of a watch

A wound-up spring stores energy because it is deformed. This stored energy is called elastic potential energy. The spring itself is not moving in a way that constitutes kinetic energy in this context; its energy is stored due to its configuration.

Option 3: Flowing water

Water that is flowing is in motion. Since kinetic energy is the energy of motion, flowing water is a direct example of kinetic energy. The faster the water flows and the greater its mass, the more kinetic energy it has.

Option 4: Compressed gas in an overhead tank

Compressed gas in a tank has potential energy stored within it due to the compression. Similar to the wound-up spring, this is a form of potential energy (related to the work done to compress the gas) rather than kinetic energy related to the bulk movement of the gas.

Conclusion

Based on the definition of kinetic energy as the energy of motion, flowing water is the correct example among the given options.