Conservation of Energy & Heat Transfer

As the ball falls, its gravitational potential energy (GPE) converts into kinetic energy (KE) while the total energy of the system remains constant. Initially, the ball has 150 J of GPE when released from rest. As it descends, this energy transforms into KE. Just before hitting the ground, all the GPE has converted into KE, resulting in a KE of 150 J. Thus, the energy is conserved, with the total energy at the start (150 J) equating to the KE just before impact.

At the midpoint of a falling ball's path, the gravitational potential energy (GPE) is converted into kinetic energy (KE). Since energy is conserved in the absence of air resistance, the total mechanical energy remains constant. At this midpoint, the ball has lost half of its initial GPE, which has been converted into KE. Therefore, both GPE and KE are equal, each representing half of the total energy. This relationship illustrates the energy transformation occurring during the ball's descent.

In a closed system, the total amount of energy remains constant; it cannot be created or destroyed. Instead, energy can change forms, such as from kinetic to potential energy or vice versa. For instance, as an object falls, its potential energy converts to kinetic energy, but the total energy remains unchanged. This principle underpins many physical processes and ensures that energy transformations adhere to the law of conservation. Thus, the statement accurately reflects the behavior of energy in a closed system.

As the ball reaches its maximum height, it possesses maximum gravitational potential energy due to its elevated position. When the ball begins to fall, this potential energy is converted into kinetic energy, which is the energy of motion. As the ball descends, the gravitational force accelerates it, increasing its velocity and thereby its kinetic energy, while the potential energy decreases until it reaches the ground. This transformation illustrates the principle of conservation of energy, where energy shifts between different forms but remains constant in total.

The SI unit for temperature is indeed the kelvin (K), which is part of the International System of Units (SI). The kelvin is defined based on the absolute temperature scale, where 0 K represents absolute zero, the point at which molecular motion ceases. This unit is widely used in scientific contexts to ensure consistency and accuracy in temperature measurements, distinguishing it from other temperature scales like Celsius and Fahrenheit.

As temperature rises, particles in a substance absorb energy, causing them to vibrate and move more vigorously. This increased kinetic energy leads to a greater distance between particles, resulting in an expansion of the substance's volume. This behavior is particularly evident in gases and liquids, where the increased energy allows particles to overcome intermolecular forces, thereby increasing the space they occupy. Consequently, as temperature increases, the volume of the substance also tends to increase.

When a substance expands or contracts, the spacing between its particles changes due to variations in temperature or pressure. During expansion, particles move further apart, increasing the spacing, while during contraction, they come closer together, decreasing the spacing. This change in spacing directly affects the volume of the substance without altering the size, number, mass, or shape of the particles themselves. Thus, spacing is the key property that changes with expansion and contraction.