Motion And Force

An artificial satellite orbiting the Earth is continuously falling toward the Earth due to gravitational attraction, but because it also has a tangential (sideways) velocity, it keeps missing the Earth — thus staying in orbit. The gravitational force of the Earth acts as the centripetal force, providing the necessary acceleration that keeps the satellite moving in its circular or elliptical path around the planet. Hence, the satellite doesn’t fall down; instead, it is in continuous free fall, balanced by its orbital motion.

A ball bearing is a type of Rolling element bearing that uses the ball to maintain the separation between the bearing races. The purpose of round ball bearings is to reduce the surface area of contact between the object being moved and the one which is providing the power. Thus, reduced area means less friction and more efficiency. The balls have a much lower coefficient of friction than the two flat surfaces sliding against each other. 

**Statement A is incorrect:** Gravity is actually the weakest of the four fundamental forces for a given distance. **Statement B is correct:** Electromagnetism acts only on charged particles, where the charge can be negative or positive. **Statement C is correct:** The weak force is responsible for the existence and structure of atomic nuclei, including radioactivity and nuclear fusion. **Statement D is correct:** Strong nuclear force is responsible for holding protons and neutrons together inside the atomic nucleus and is 100 times stronger than electromagnetism.

During photosynthesis, solar energy is converted into chemical energy and stored in sugar molecule bonds. This chemical bond energy is potential (stored) energy. 

Gravitational waves are ripples in the fabric of spacetime, predicted by Einstein's theory of general relativity. eLISA is a space-based gravitational wave observatory that can detect and study these gravitational waves. It is a joint project of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). eLISA is designed to detect gravitational waves from astronomical sources such as merging black holes and neutron stars. It would use laser interferometry to measure the tiny distortions in spacetime caused by passing gravitational waves. Detecting gravitational waves would provide important insights into the nature of gravity and the evolution of the universe.

The merger of black holes is expected to generate powerful gravitational waves. Gravitational waves are ripples in spacetime caused by accelerating massive objects. Detecting these waves with instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory) allows us to study these events even when they are too far away or obscured to observe directly. This opens a new window for astronomical observations.

The description mentions three spacecraft in an equilateral triangle formation with million-kilometre sides using lasers for measurement. This matches the design of the Evolved Laser Interferometer Space Antenna (eLISA) mission. eLISA is a proposed space observatory aiming to detect gravitational waves using precisely positioned spacecraft. Voyager-2 and New Horizons are single spacecraft on exploration missions, not designed for gravitational wave detection. LISA Pathfinder was a precursor mission to test technologies for eLISA, not the full mission itself. Therefore, based on the details provided, the experiment refers to the Evolved LISA mission.