• Helicopters achieve flight by using the principle of conservation of linear momentum.
• The rotating blades exert a force on the stationary air, causing it to move towards the ground, gaining momentum.
• Due to Newton's third law, there is an equal and opposite upward force on the helicopter through the rotors, allowing it to hover.

Example: Imagine a toy helicopter. When you switch it on, the blades start rotating. The faster they rotate, the more air they push downwards. This results in an upward force on the helicopter that allows it to take off or hover.

• Seat belts and airbags increase the time taken for the car's occupants to stop in an accident, reducing the force experienced and thereby the potential damage.
• These safety measures work because of the equation: force × time = change in momentum.
• In a crash, a person in a car loses kinetic energy and momentum, whether they hit the windscreen or are restrained by the seatbelt. The difference lies in the time it takes to lose this momentum - a longer time means less force and less damage.

Example: Think of throwing a tomato at a brick wall versus a sheet. The brick wall stops the tomato instantly, causing it to splatter (like a person hitting a windshield). The sheet, however, slows the tomato down gradually, reducing the chance of it breaking (like a person restrained by a seatbelt).

• Momentum conservation plays a vital role in a nuclear power station.
• In reactors, the process of moderation relies on momentum transfer as the neutrons interact (collide) with the moderator atoms.
• Nuclear engineers use conservation of momentum to predict the number of collisions needed before a neutron loses sufficient energy to be effective in promoting further fissions, influencing the shape and size of the moderator in the reactor.

Example: Imagine a pool game. When the cue ball (the neutron) hits another ball (the moderator atom), it slows down, transferring its energy to the other ball. This process is similar to how a nuclear reactor works.